Chem 180 Exam 3
Write a balanced equation for the cell reaction.
2Al(s)+3Co2+(aq)→3Co(s)+2Al3+(aq)
What is the sign of ΔSsurr for an exothermic reaction?
+
Consider the following gas-phase reaction of A2 (shaded spheres) and B2 (unshaded spheres): A2(g) + B2(g) ↔ 2 AB(g) ΔG ° = +25 kJ Which of the above reaction mixtures has the least spontaneous forward reaction?
(4)
Predict the sign of the entropy change in the system for each of the following processes. A solid sublimes A liquid freezes AgI precipitates from a solution containing Ag+ and I− ions Gaseous CO2 bubbles out of a carbonated beverage
+ - - +
Calculate the cell potential at 25°C for the cell Fe(s) | (Fe2+(0.100 M) || Pd2+(1.0 × 10-5 M) | Pd(s) given that the standard reduction potential for Fe2+/Fe is -0.45 V and for Pd2+/Pd is +0.95 V.
+1.28 V
For the reaction 2 Al(s) + 3 Co2+(aq) → 2 Al3+(aq) + 3 Co(s), ΔG∘ is -799 kJ. What is E° for a standard cell based on this reaction?
+1.38 V
What is the standard cell potential for the reaction below? Mg(s) + Br2(l) → Mg2+(aq) + 2 Br-(aq) The standard reduction potential is -2.37 V for the Mg2+/Mg half-cell and +1.09 V for the Br2/Br- half-cell.
+3.46 V
If a metal begins with a +3 oxidation number, which of the following oxidation numbers would indicate that the metal has been oxidized?
+4
What substance is produced at the anode during the electrolysis of molten calcium bromide, CaBr2? Assume standard conditions.
2Br−→Br2+2e−
Aqueous copper (II) ion reacts with aqueous iodide ion to yield solid copper (I) iodide and aqueous iodine. Write the balanced net ionic equation. Assign oxidation numbers to all species present. Identify the oxidizing agent. Identify the reducing agents.
2Cu2+(aq)+4I−(aq)→2CuI(s)+I2(aq) Cu2+, I−, Cu(CuI) ,I(CuI), I2 +2,-1,+1,-1,0 Cu2+ I−
Consider the following electrochemical cell. Is the cell a galvanic or an electrolytic cell?
Is the cell a galvanic or an electrolytic cell?
What is the sign of ΔSsurr for an endothermic reaction?
-
Cd(s)+Sn2+(aq)→Cd2+(aq)+Sn(s) Write the anode half-reaction.
Cd(s)→Cd2+(aq)+2e−
What is the entropy of 10 molecules in a system of 100000 boxes?
S = 1.59×10−21 J⋅K−1
ΔG = ΔG° for a reaction
if Q = 1.
Consider the following spontaneous reaction of A2 molecules (red) and B2 molecules (blue). Write a balanced equation for the reaction. What is the sign of ΔH for the reaction? What is the sign of ΔS for the reaction? What is the sign of ΔG for the reaction?
2A2+B2→2A2B ΔH < 0 ΔS < 0 ΔG < 0
Give an equation that relates the entropy change in the surroundings to the enthalpy change in the system.
ΔSsurr=−ΔH/T
In a neutral compound, the sum of the oxidation states is zero. Note that the sign of the oxidation states and the number of atoms associated with each oxidation state must be considered. In H2O, for example, each hydrogen atom has an oxidation state of +1 and each oxygen atom has an oxidation state of −2 for a total of 2(+1)+(−2)=0. What is the oxidation state of an individual sulfur atom in BaSO4? What is the oxidation state of an individual nitrogen atom in HNO3? In an ion, the sum of the oxidation states is equal to the overall ionic charge. Note that the sign of the oxidation states and the number of atoms associated with each oxidation state must be considered. In OH−, for example, the oxygen atom has an oxidation state of −2 and the hydrogen atom has an oxidation state of +1, for a total of (−2)+(+1)=−1. What is the oxidation state of an individual sulfur atom in SO32−? What is the oxidation state of each individual carbon atom in C2O42−?
+6 +5 +4 +3
Solid NaHCO3 is heated to 90°C. At equilibrium the total pressure of the gases produced is 0.545 atm. Calculate ΔG° at 90°C for the reaction 2 NaHCO3(s) ↔ Na2CO3(s) + H2O(g) + CO2(g).
+7.85 kJ
What are the signs, (+, -, or 0) of ΔH, ΔS, and ΔG for the following spontaneous reaction of A atoms (red) and B atoms (blue)? The sign of ΔH The sign of ΔS The sign of ΔG
- - -
The standard potential for the following galvanic cell is +0.90 V: 3 Cu2+(aq) + 2 Ga(s) ↔ 3 Cu(s) + 2 Ga3+(aq) Given that the standard reduction potential for the Cu2+/Cu half-cell is +0.34 V, what is the standard reduction potential for the Ga3+/Ga half-cell?
-0.56 V
Calculate the standard free energy change at 25°C for the reaction 2 NO(g) + O2(g) → 2 NO2(g).
-72.6 kJ
The following pictures represent equilibrium mixtures for the interconversion of A molecules (red) and X, Y, or Z molecules (blue). What is the sign of ΔG∘ for the first reaction? What is the sign of ΔG∘ for the second reaction? What is the sign of ΔG∘ for the third reaction?
0 - +
Consider a galvanic cell that uses the reaction Cu(s)+2Fe3+(aq)→Cu2+(aq)+2Fe2+(aq) What is the potential of a cell at 25 ∘C that has the following ion concentrations? [Fe3+]= 1.8×10−4 M , [Cu2+]= 0.26 M , [Fe2+]= 0.15 M
0.27 V
Calculate the potential of a galvanic cell that uses the reaction H2(g) + 2OH−(aq) + Sn2+(aq) → Sn(s) + 2H2O(l) at 25 °C when [OH−] = 0.010 M, [Sn2+] = 0.020 M, and PH2 = 1.0 atm (E° = 0.69 V).
0.52 V
In the process of oxidizing I− to I2, SO42− is reduced to SO2. How many moles of SO2 are produced in the formation of one mole of I2?
1 mol The iodine half-reaction generates two electrons. The sulfur half-reaction consumes two electrons. So we can determine that I2 and SO2 are produced in a 1:1 mole ratio without ever writing the full equation.
Which state has the higher entropy? 1 mol of N2 gas at 273 K and 0.25 atm 1 mol of N2 gas at STP
1 mol of N2 gas at 273 K and 0.25 atm
Which state has the higher entropy? 1 mol of N2 gas at 273 K in a volume of 11.2 L 1 mol of N2 gas at STP
1 mol of N2 gas at STP
A constant current of 2.00 A is passed through a sample of water for 120.0 minutes in an electrolytic cell. How many grams of oxygen are produced?
1.19 g
The standard potential for the following galvanic cell is 3.16 V : Al(s)|Al3+(aq)||Au3+(aq)|Au(s) Look up the standard reduction potential for the Al3+/Al half-cell in the table above and calculate the standard reduction potential for the Au3+/Au half-cell.
1.50 V
What is the absolute entropy of the disordered state of a crystal of BCl2Br containing 100 molecules, if each trigonal planar molecule is oriented randomly in one of three possible ways? (k = 1.38 × 10−23 J/K)
1.52 × 10−21 J/K
If the standard cell potential for the galvanic cell Pt(s) | Fe2+(aq), Fe3+(aq) || Ce4+(aq), Ce3+(aq) | Pt(s) is 0.84 V, what is the standard reduction potential for the Ce4+(aq) /Ce3+ half-cell (E° for Fe2+/Fe3+ half-cell = −0.77 V)?
1.61 V
Estimate ΔStotal, the total entropy change, for the following reaction at 25° C: 2 CO(g) + O2(g) → 2 CO2(g) given ΔG°f for CO(g) is -137.2 kJ/mol and ΔG°f for CO2(g) is -394.4 kJ/mol.
1.73 × 103 J/K
What is the total entropy change for the reaction 2O3(g) → 3O2(g) at 25 °C? (ΔH f&176; for O3(g) = 143 kJ/mole; S° for O2(g) = 205.0 J/( K·mol); S° for O3(g) = 238.8 J/( K·mol))
1097 J/K
Under which of the following conditions would one mole of Kr have the highest entropy, S?
157°C and 55 L
ΔS° = - 198.7 J/K for the reaction shown below. Calculate S° for NH3(g). N2(g) + 3 H2(g) → 2 NH3(g)
192.3 J/K•mol
CaO can be used as a drying agent. One such application occurs when water is added to dry concrete or cement. The reaction that occurs is CaO(s)+H2O(l)⇌Ca(OH)2(s) The product is commonly called slaked lime. Assuming the commonly used standard-state temperature of 25∘C, calculate ΔSuniv for this reaction using table from the table below.
193 J/K
What is the balanced chemical equation for the galvanic cell reaction expressed using shorthand notation below? Al(s) | Al3+(aq) || Cd 2+(aq) | Cd(s)
2 Al(s) + 3 Cd 2+(aq) → 2 Al3+(aq) + 3 Cd(s)
Consider the galvanic cell shown below. What is the balanced equation for the cell reaction?
2 Al(s) + 3 Co2+(aq) → 2 Al3+(aq) + 3 Co(s)
Balance the following equation: K2CrO4+Na2SO3+HCl→KCl+Na2SO4+CrCl3+H2O Generally coefficients of 1 are omitted from balanced chemical equations. When entering your answer, include coefficients of 1 as required for grading purposes.
2,3,10,4,3,2,5 The balanced reaction will be 2K2CrO4+3Na2SO3+10HCl→4KCl+3Na2SO4+2CrCl3+5H2O
If a constant current of 1.50 × 108 A is passed through a molten mixture of aluminum oxide and cryolite for 4.00 hour ________ kg of aluminum can be produced.
201
Chromium can be electroplated from an aqueous solution containing sulfuric acid and chromic acid, H2CrO4. What current is required to deposit chromium at a rate of 1.25 g/min?
232 A
Write balanced equation for the anode reaction. Write balanced equation for the cathode reaction. Write balanced equation for the overall cell reaction.
2H2O(l)→O2(g)+4H+(aq)+4e− Ni2+(aq)+2e−→Ni(s) 2Ni2+(aq)+2H2O(l)→2Ni(s)+O2(g)+4H+(aq)
Predict the half-cell reactions that occur when aqueous solutions of the following salts are electrolyzed in a cell with inert electrodes. What is the overall cell reaction in each case? anode reaction for LiI cathode reaction for LiI: overall cell reaction for LiI: anode reaction for CuSO4 cathode reaction for CuSO4 overall cell reaction for CuSO4 anode reaction for Cs2SO4 cathode reaction for Cs2SO4 overall cell reaction Cs2SO4
2I−(aq)→I2(s)+2e− 2H2O(l)+2e−→H2(g)+2OH−(aq) 2I−(aq)+2H2O(l)→I2(s)+H2(g)+2OH−(aq) 2H2O(l)→O2(g)+4H+(aq)+4e− Cu2+(aq)+2e−→Cu(s) 2Cu2+(aq)+2H2O(l)→O2(g)+4H+(aq)+2Cu(s) 2H2O(l)→O2(g)+4H+(aq)+4e− 4H2O(l)+4e−→2H2(g)+4OH−(aq) 2H2O(l)→2H2(g)+O2(g)
What substance is produced at the anode during the electrolysis of a mixture of molten calcium bromide, CaBr2(l), and molten magnesium iodide, MgI2(l)? Assume standard conditions.
2I−→I2+2e−
Write balanced net ionic equations for the following reactions in basic solution: MnO−4(aq)+IO−3(aq)⟶MnO2(s)+IO−4(aq) Cu(OH)2(s)+N2H4(aq)⟶Cu(s)+N2(g) Fe(OH)2(s)+CrO2−4(aq)⟶Fe(OH)3(s)+Cr(OH)−4(aq) H2O2(aq)+ClO−4(aq)⟶ClO−2(aq)+O2(g)
2MnO4−(aq)+3IO3−(aq)+H2O(l)→2MnO2(s)+3IO4−(aq)+2OH−(aq) 2Cu(OH)2(s)+N2H4(aq)→2Cu(s)+N2(g)+4H2O(l) 3Fe(OH)2(s)+CrO42−(aq)+4H2O(l)→Cr(OH)4−(aq)+OH−(aq)+3Fe(OH)3(s) ClO4−(aq)+2H2O2(aq)→ClO2−(aq)+2H2O(l)+2O2(g)
Balance the following net ionic equation by the half-reaction method. The reaction takes place in acidic solution. NO3−(aq)+Cu(s)→NO(g)+Cu2+(aq) (Unbalanced)
2NO3−(aq)+8H+(aq)+3Cu(s)→3Cu2+(aq)+2NO(g)+4H2O(l)
Write balanced net ionic equations for the following reactions in basic solution. S2O32−(aq)+I2(aq)→S4O62−(aq)+I−(aq) Mn2+(aq)+H2O2(aq)→MnO2(s)+H2O(l) Zn(s)+NO3−(aq)→NH3(aq)+Zn(OH)42−(aq) Bi(OH)3(s)+Sn(OH)3−(aq)→Bi(s)+Sn(OH)62−(aq)
2S2O32−(aq)+I2(aq)→S4O62−(aq)+2I−(aq) Mn2+(aq)+H2O2(aq)+2OH−(aq)→MnO2(s)+2H2O(l) 4Zn(s)+NO3−(aq)+7OH−(aq)+6H2O(l)→NH3(aq)+4Zn(OH)42−(aq) 3Sn(OH)3−(aq)+2Bi(OH)3(s)+3OH−(aq)→3Sn(OH)62−(aq)+2Bi(s)
For a particular cell based on the reaction: 3 AgCl(s) + Al(s) → 3 Ag(s) + Al3+(aq) + 3 Cl-(aq) E = +1.750 V and E° = +1.884 V at 25°C. What is the value of the equilibrium constant, K, at 25°C for the reaction?
3.0 × 1095
Calculate the equilibrium constant, K, at 25∘C for the galvanic cell reaction shown below: 8H+(aq)+5Fe2+(aq)+MnO−4(aq)→Mn2+(aq)+5Fe3+(aq)+4H2O(l) E∘ = 0.74V
3.2 × 1062
What would be an expression for the entropy change for 2.44 moles of an ideal gas that undergoes a change in pressure from 4.00 atm to 1.00 atm at constant temperature?
3.38 moles ⋅ R
Which electron on an atom of copper would have the highest value of W in the Boltzmann formula?
3d
The vapor pressure of water changes with temperature, as shown here. A student designs an ammeter (a device that measures electrical current) that is based on the electrolysis of water into hydrogen and oxygen gases. When electrical current of unknown magnitude is run through the device for 3.50 min , 12.5 mL of water-saturated H2(g) is collected. The temperature and pressure of the system are 25 ∘C and 715 torr. How many moles of hydrogen gas are produced? Calculate the magnitude of the current in amperes if the number of moles of hydrogen gas produced is 4.65×10−4 mol (from part A).
4.65×10−4 mol 0.427 A
Write balanced net ionic equations for the following reactions in acidic solution: MnO−4(aq)+C2H5OH(aq)⟶Mn2+(aq)+CH3CO2H(aq) H2O2(aq)+Cr2O2−7(aq)⟶O2(g)+Cr3+(aq) Sn2+(aq)+IO−4(aq)⟶Sn4+(aq)+I−(aq) PbO2(s)+Cl−(aq)⟶PbCl2(s)+O2(g)
4MnO4−(aq)+5C2H5OH(aq)+12H+(aq)→4Mn2+(aq)+5CH3CO2H(aq)+11H2O(l) 3H2O2(aq)+Cr2O72−(aq)+8H+(aq)→2Cr3+(aq)+7H2O(l)+3O2(g) 4Sn2+(aq)+IO4−(aq)+8H+(aq)→I−(aq)+4Sn4+(aq)+4H2O(l) 2PbO2(s)+4Cl−(aq)+4H+(aq)→2PbCl2(s)+2H2O(l)+O2(g)
Calculate ∆G° (in kilojoules) at 25 °C for the reaction O2(g) + 4H+(aq) + 4Cl−(aq) → 2H2O(l) + 2Cl2(g) , which has a standard cell potential = −0.13 V.
5.0 × 101 kJ
What is the equilibrium constant for the reaction Sn4+(aq) + 2I−(aq) → Sn2+(aq) + I2(s) at 25 °C? E° = 0.15 V for a Sn4+/Sn2+ half-cell E° = 0.54 V for a I2/I− half-cell
6.7 × 10−14
At high temperatures, boron carbide vaporizes according to B4C(s) ↔ 4 B(g) + C(s) At 2500 K, the equilibrium pressure of B(g) is 0.0342 mm Hg over a mixture of 0.300 mol B4C(s) and 0.500 mol C(s). Calculate ΔG∘ for this process.
832 kJ
What is the standard free-energy change (in kJ) at 25 °C for the reaction 2A(g) + B(g) ↔ 2C(g)? (K p = 2.2 × 10−2)
9.5 kJ
Consider the gas-phase reaction of AB3 and A2 molecules Write a balanced equation for the reaction. What is the sign of the entropy change for the reaction?
A2+AB3→3AB ΔS > 0
Consider the galvanic cell shown below. Identify the anode and cathode, and indicate the direction of Na+ ion and NO3- ion flow from the salt bridge.
Al is the anode and Co is the cathode; NO3- ions flow into half-cell compartment (A) and Na+ ions flow into half-cell compartment (B).
According to the table, which will reduce water but not Mg2+?
Al(s)
What is the shorthand notation for the cell?
Al(s)|Al3+(aq)||Co2+(aq)|Co(s)
2Al(s)+3Cd2+(aq)→2Al3+(aq)+3Cd(s) Write the anode half-reaction.
Al(s)→Al3+(aq)+3e−
Predict the anode, cathode, and overall cell reactions when an aqueous solution of each of the following salts is electrolyzed in a cell having inert electrodes. Ag2SO4 Anode: Cathode: Overall: Ca(OH)2 Anode: Cathode: Overall: KI Anode: Cathode: Overall:
Anode: 2H2O(l)→O2(g)+4H+(aq)+4e− Cathode: 4Ag+(aq)+4e−→4Ag(s) Overall: 4Ag+(aq)+2H2O(l)→O2(g)+4H+(aq)+4Ag(s) A: 4OH−(aq)→O2(g)+2H2O(l)+4e− C: 4H2O(l)+4e−→2H2(g)+4OH−(aq) O: 2H2O(l)→2H2(g)+O2(g) A: 2I−(aq)→I2(s)+2e− C: 2H2O(l)+2e−→H2(g)+2OH−(aq) O: 2I−(aq)+2H2O(l)→I2(s)+H2(g)+2OH−(aq)
Estimate the normal boiling point of 2-methylheptane using Trouton's rule [estimating that ΔS is approximately 87-88 J/(K⋅mol)] assuming that the enthalpy of vaporization, Hvap = 33.26 kJ/mol , remains relatively constant.
Boiling point of 2-methylheptane = 382 K
Which element is oxidized in this reaction? 2CuO+C→2Cu+CO2 Which substance is the oxidizing agent in this reaction? 2CuO+C→2Cu+CO2 Which element is reduced in this reaction? 2KMnO4+3Na2SO3+H2O→2MnO2+3Na2SO4+2KOH Which substance is the reducing agent in this reaction? 2KMnO4+3Na2SO3+H2O→2MnO2+3Na2SO4+2KOH
C is oxidized CuO is the oxidizing agent. Mn is reduced Na2SO3 is the reducing agent.
Which substance in each of the following pairs would you expect to have the higher standard molar entropy? C2H2(g) or C2H6(g) CO2(g) or CO(g) I2(s) or I2(g) C2H5OH(g) or C2H5OH(l)
C2H6(g) CO2(g) I2(g) C2H5OH(g)
What substance is produced at the cathode during the electrolysis of molten calcium bromide, CaBr2? Assume standard conditions.
Ca2++2e−→Ca
2Al(s)+3Cd2+(aq)→2Al3+(aq)+3Cd(s) Write the cathode half-reaction.
Cd2+(aq)+2e−→Cd(s)
Which is the stronger oxidizing agent, Cl2(g) or Ag+(aq)? Which is the stronger reducing agent, Fe(s) or Mg(s)?
Cl2(g) Mg(s)
Which shorthand notation correctly represents the reaction Co(s) + Cl2(g) → Co2+(aq) + 2Cl−(aq) occurring in a galvanic cell?
Co(s) | Co2+(aq) || Cl2(g) | Cl−(aq) | Pt(s)
Write balanced equation for overall cell reactions of the following galvanic cell Co(s)|Co2+(aq)||Cu2+(aq)|Cu(s)
Co(s)+Cu2+(aq)→Co2+(aq)+Cu(s)
Write balanced equation for the anode of the following galvanic cell Co(s)|Co2+(aq)||Cu2+(aq)|Cu(s)
Co(s)→Co2+(aq)+2e−
Label the diagram according to the components and processes of a voltaic cell. The half-cell is a chamber in the voltaic cell where one half-cell is the site of the oxidation reaction and the other half-cell is the site of the reduction reaction. Type the half-cell reaction that takes place at the anode for the cobalt-silver voltaic cell. Indicate the physical states using the abbreviation (s), (l), or (g) for solid, liquid, or gas, respectively. Use (aq) for an aqueous solution. Do not forget to add electrons in your reaction. The half-cell is a chamber in the voltaic cell where one half-cell is the site of an oxidation reaction and the other half-cell is the site of a reduction reaction. Type the half-cell reaction that takes place at the cathode for the cobalt-silver voltaic cell. Indicate physical states using the abbreviation (s), (l), or (g) for solid, liquid, or gas, respectively. Use (aq) for an aqueous solution. Do not forget to add electrons in your reaction. What is the net cell reaction for the cobalt-silver voltaic cell?
Co(s)→Co3+(aq)+3e− Ag+(aq)+e−→Ag(s) Co(s)+3Ag+(aq)→Co3+(aq)+3Ag(s)
Activity Series One of the simplest types of oxidation-reduction reactions is the reaction of an aqueous cation with a free element. Whether or not a cation-element combination will produce a net change depends on the relative tendency of the various species to gain or lose electrons. An activity series ranks elements in order of their tendency to act as reducing agents. The elements at the top of the activity series are strong reducing agents and are easily oxidized. The elements at the bottom of the series are weak reducing agents. In other words, the reactions near the bottom tend to go backward rather than forward. The activity series can be used to predict reactions using the simple guideline: Any element higher on the activity series will reduce the cation of any element lower on the activity series. An abbreviated series is shown in the following: Oxidation reaction Strongly reducing K → K++e− Ca → Ca2++2e− Mn → Mn2++2e− Cr → Cr3++3e− Fe → Fe2++2e− Sn → Sn2++2e− H2 → 2H++2e− Cu → Cu2++2e− Pt → Pt2++2e− Au → Au3++3e− Weakly reducing
Consider four beakers labeled A, B, C, and D, each containing an aqueous solution and a solid piece of metal. Identity the beakers in which a chemical reaction will occur and those in which no reaction will occur. A. Mn(s)+Ca(NO3)2(aq) B. KOH(aq)+Fe(s) C. Pt(NO3)2(aq)+Cu(s) D. Cr(s)+H2SO4(aq)
What is the change that (at constant pressure) is most likely to produce the largest change in entropy? (melting point of ethanol = −117 °C; boiling point of ethanol = 78 °C) Heating 10.0 g of ethanol from 85 °C to 105 °C Cooling 10.0 g of ethanol from 65 °C to 45 °C Heating 10.0 g of ethanol from −186 °C to −166 °C Cooling 10.0 g of ethanol from 92 °C to 72 °C
Cooling 10.0 g of ethanol from 92 °C to 72 °C
Cr2O2−7(aq)+6Fe2+(aq)+14H+(aq)→2Cr3+(aq)+6Fe3+(aq)+7H2O(l) Write the cathode half-reaction.
Cr2O72−(aq)+14H+(aq)+6e−→2Cr3+(aq)+7H2O(l)
For the galvanic cell reaction, expressed below using shorthand notation, what half-reaction occurs at the cathode? Zn(s) | Zn2+(aq) || Cu 2+(aq) | Cu(s)
Cu 2+(aq) + 2 e- → Cu(s)
Write balanced equation for the cathode of the following galvanic cell Co(s)|Co2+(aq)||Cu2+(aq)|Cu(s)
Cu2+(aq)+2e−→Cu(s)
For the reaction 2Co3+(aq)+2Cl−(aq)→2Co2+(aq)+Cl2(g). E∘=0.483 V what is the cell potential at 25 ∘C if the concentrations are [Co3+]= 0.476 M , [Co2+]= 0.803 M , and [Cl−]= 0.857 M and the pressure of Cl2 is PCl2= 3.50 atm ?
E = 0.450 V
Consider a galvanic cell that uses the reaction 2Ag+(aq)+Sn(s)→2Ag(s)+Sn2+(aq) Calculate the potential at 25∘C for a cell that has the following ion concentrations: [Ag+] = 1.0×10−2 M , 3.0×10−2 M .
E = 0.87 V
For an electrolytic cell
E is negative and ΔG is positive for the cell reaction.
Given: Ag+(aq) + e- → Ag(s) E° = +0.799 V AgI(s) + e- → Ag(s) + I-(aq) E° = -0.152 V Ni2+(aq) + 2 e- → Ni(s) E° = -0.267 V Which of the following reactions should be spontaneous under standard conditions? I. 2 AgI(s) + Ni(s) → 2 Ag(s) + 2 I-(aq) + Ni2+(aq) II. Ag+(aq) + I-(aq) → AgI(s)
I and II are both spontaneous.
Predict the sign of ΔS for each of the following processes, which occur at constant temperature. I. The volume of 2.0 moles of O2(g) increases from 44 L to 52 L. II. The pressure of 2.0 moles of O2(g) increases from 1.0 atm to 1.2 atm.
I: ΔS= positive; II: ΔS= negative
State the second law of thermodynamics.
In any spontaneous process, the total entropy of a system and its surroundings always increases
Qualitative Predictions about Entropy
Entropy is the randomness of a system. At the molecular level, entropy can be described in terms of the possible number of different arrangements of particle positions and energies, called microstates. The more microstates the system has, the greater its entropy. Microstates depend on molecular motion. Molecules may undergo three different types of motion: translational motion, vibrational motion, and rotational motion. During translational motion, the entire molecule moves in one direction. During vibrational motion, atoms in a molecule move toward and away from one another. During rotational motion, molecules rotate or spin. The number of molecules, the space available for the molecules, and the energy available to the molecules will impact the number of microstates. Another way of looking at entropy is that the universe is moving toward a broader distribution of energy. The universe has a constant amount of energy as stated in the first law of thermodynamics. The universe started with low entropy (concentrated in the moment before the "big bang") and the entropy has since been constantly increasing by distributing this energy. Heat distribution from high temperature to low temperature is a another example of this phenomenon.
What is the relationship between the standard cell potentials, E°, for the following two galvanic cell reactions? I. 2 Ag+(aq) + Sn2+(aq) → Sn4+(aq) + 2 Ag(s) II. Ag(s) + 1/2 Sn4+(aq) → 1/2 Sn2+(aq) + Ag+(aq)
E°(I) = - E°(II)
In thermodynamics, we determine the spontaneity of a reaction by the sign of ΔG. In electrochemistry, spontaneity is determined by the sign of E∘cell. The values of ΔG and E∘cell are related by the following formula: ΔG∘=−nFE∘cell where n is the number of moles of electrons transferred and F=96,500J/V⋅mol e− is the Faraday constant. The standard reduction potentials of lithium metal and chlorine gas are as follows: In a galvanic cell, the two half-reactions combine to 2Li(s)+Cl2(g)→2Li+(aq)+2Cl−(aq) Calculate the cell potential of this reaction under standard reaction conditions. Calculate the free energy ΔG∘ of the reaction. What can be said about the spontaneity of this reaction?
E∘ = 4.40 V ΔG∘ = -849 kJ The reaction is spontaneous as written.
The standard potential for the following galvanic cell is 0.40 V: Zn(s)|Zn2+(aq)||Eu3+(aq), Eu2+(aq)|Pt(s) (Europium, Eu, is one of the lanthanide elements.) Calculate the standard reduction potential for the Eu3+/Eu2+ half-cell, if Zn2+(aq)+2e−→Zn(s), E∘ = -0.76 V
E∘ = -0.36 V
Calculate E∘ for each of the following reactions, and tell which are spontaneous under standard-state conditions. 2Fe2+(aq)+Pb2+(aq)→2Fe3+(aq)+Pb(s) Mg(s)+Ni2+(aq)→Mg2+(aq)+Ni(s) Tell which are spontaneous under standard-state conditions.
E∘ = -0.90 V E∘ = 2.11 V Mg(s)+Ni2+(aq)→Mg2+(aq)+Ni(s)
If a reaction has an equilibrium constant K<1, is E∘ positive or negative?
E∘ is negative.
In a galvanic cell, a spontaneous redox reaction occurs. However, the reactants are separated such that the transfer of electrons is forced to occur across a wire. The resulting cell potential is measured in volts (V) and is defined by the equation given below: E∘cell=E∘red(cathode)−E∘red(anode) A table of standard reduction potentials gives E∘red values for common half-reactions. Calculate the standard potential for the following galvanic cell: Fe(s) | Fe2+(aq) || Ag+(aq) | Ag(s) which has the overall balanced equation: Fe(s)+2Ag+(aq)→Fe2+(aq)+2Ag(s)
E∘cell = 1.25 V
Nickel and aluminum electrodes are used to build a galvanic cell. The standard reduction potential for the nickel(II) ion is −0.26 V and that of the aluminum(III) ion is −1.66V. What is the theoretical cell potential assuming standard conditions? Complete the sentences describing the cell.
E∘cell = 1.40 V
Calculate the standard cell potential given the following standard reduction potentials: Al3++3e−→Al;E∘=−1.66 V Sn2++2e−→Sn;E∘=−0.140 V
E∘cell = 1.52 V
Write a balanced equation for the overall cell reaction represented by the following shorthand notation: Fe(s)|Fe2+(aq)||Br2(l)|Br−(aq)|Pt(s)
Fe(s)+Br2(l)→Fe2+(aq)+2Br−(aq)
The equilibrium constant, K, for a redox reaction is related to the standard potential, E∘, by the equation lnK=nFE∘RT where n is the number of moles of electrons transferred, F (the Faraday constant) is equal to 96,500 C/(mol e−) , R (the gas constant) is equal to 8.314 J/(mol⋅K) , and T is the Kelvin temperature. Use the table of standard reduction potentials given above to calculate the equilibrium constant at standard temperature (25 ∘C) for the following reaction: Calculate the standard cell potential (E∘) for the reaction X(s)+Y+(aq)→X+(aq)+Y(s) if K = 2.32×10−3
Fe(s)+Ni2+(aq)→Fe2+(aq)+Ni(s) E∘ = -0.156 V
What is the shorthand notation for a galvanic cell that uses the reaction 2Fe(s)+Cr2O2−7(aq)+14H+(aq)→2Fe3+(aq)+2Cr3+(aq)+7H2O(l)?
Fe(s)|Fe3+(aq)||Cr2O2−7(aq),Cr3+(aq)|Pt(s)
Write balanced equation for the anode of the following galvanic cell Fe(s)|Fe2+(aq)||O2(g)|H+(aq),H2O(l)|Pt(s)
Fe(s)→Fe2+(aq)+2e−
Cr2O2−7(aq)+6Fe2+(aq)+14H+(aq)→2Cr3+(aq)+6Fe3+(aq)+7H2O(l) Write the anode half-reaction.
Fe2+(aq)→Fe3+(aq)+e−
What is the Fe2+ : Sn2+ concentration ratio in the following cell at 25 ∘C if the measured cell potential is 0.35 V ? Fe(s)|Fe2+(aq)||Sn2+(aq)|Sn(s) Use data from Table 17.1 in the textbook.
Fe2+/Sn2+ = 4.5×10−2
Consider the following substances: I2(s), Fe2+(aq), Fe3+(aq). Which is the strongest oxidizing agent? Which is the weakest oxidizing agent?
Fe3+(aq) Fe2+(aq)
Which state has the higher entropy per mole of substance? Which state has the higher entropy per mole of substance? Which state has the higher entropy per mole of substance? Which state has the higher entropy per mole of substance?
H2 at 25 ∘C in a volume of 150 L O2 at 25 ∘C and 1 atm H2 at 100 ∘C and 1 atm O2 at STP
Which of the following is the correctly balanced oxidation half-reaction for the unbalanced redox equation given below? MnO4 −(aq) + H2O2(aq) →Mn2+(aq) + O2(g) →
H2O2(aq) →O2(g) + 2H+(aq) + 2e−
The cell reaction 2 Fe3+(aq) + Zn(s) → Zn2+(aq) + 2 Fe2+(aq) occurs in the galvanic cell shown above. Where should the Fe3+(aq) and Fe2+(aq) be found?
Half-cell (B) contains Fe3+(aq) and Fe2+(aq).
The reaction between carbon tetrachloride, CCl4, and water, H2O, to form carbon dioxide, CO2, and hydrogen chloride, HCl, has a ΔG∘ value of −232 kJ/mole, and so is thermodynamically favored. But when you mix carbon tetrachloride with water, no change is observed. What is a possible explanation for this? What word best describes the role that the palladium plays in the reaction between propene and hydrogen above? What did the palladium do to to increase the rate of the reaction between the propene and hydrogen?
It is a slow reaction kinetically. It is a catalyst. It lowered the activation energy of the reaction
Calculate the equilibrium constant at 25 ∘C for the reaction 4Fe2+(aq)+O2(g)+4H+(aq)→4Fe3+(aq)+2H2O(l), Using the data below Fe3+(aq)+e−→Fe2+(aq), E∘ = 0.77 V O2(g)+4H++4e−→2H2O(l), E∘ = 1.23 V
K = 1×1031
Calculate the equilibrium constant at 25 ∘C for the reaction Ni(s)+2Ag+(aq)→Ni2+(aq)+2Ag(s), if Ni2+(aq)+2e−→Ni(s), E∘ = -0.26 V, Al+(aq)+e−→Al(s), E∘ = 0.80 V
K = 6×1035
Calculate the equilibrium constant at 25 ∘C for the reaction Hg2+2(aq)→Hg(l)+Hg2+(aq) See Appendix D for standard reduction potentials.
K = 9×10−3
What is the value of K when E∘ = 0V?
K = 1
Calculate the equilibrium constant at 25 ∘C for each of the following reactions: Cd(s)+Sn2+(aq)→Cd2+(aq)+Sn(s) 2Al(s)+3Cd2+(aq)→2Al3+(aq)+3Cd(s) Cr2O2−7(aq)+6Fe2+(aq)+14H+(aq)→2Cr3+(aq)+6Fe3+(aq)+7H2O(l)
K = 6×108 K = 5×10127 K = 6×1059
If ΔG° is positive for a reaction,
K is between 0 and 1.
Acetylene, C2H2, can be converted to ethane, C2H6, by a process known as hydrogenation. The reaction is C2H2(g)+2H2(g)⇌C2H6(g) Given the following data at standard conditions (all pressures equal to 1 atm and the common reference temperature 298 K), what is the value of Kp for this reaction?
Kp = 2.7×1042
Calculate the equilibrium constant Kp at 25 ∘C for the following reaction: 2SO2(g)+O2(g)→2SO3(g), ΔG∘ = -141.8 kJ
Kp = 7.2×1024 atm−1
For the following reaction find Kp at 25°C and indicate whether Kp should increase or decrease as the temperature rises. NH4HS(s) ↔ H2S(g) + NH3(g) ΔH° = 83.47 kJ and ΔG° = 17.5 kJ at 25°C.
Kp = 8.6 × 10-4 and Kp should increase as the temperature rises.
Calculate the equilibrium constant Kp for the reaction at a temperature of 298 K. In principle, is this reaction a feasible method of removing SO2 from power-plant emissions? Assume that the partial pressure of sulfur dioxide, PSO2, is equal to the partial pressure of dihydrogen sulfide, PH2S, and therefore PSO2=PH2S. If the vapor pressure of water is 24 torr , calculate the equilibrium partial pressure of SO2 (PSO2) in the system at 298 K. Using relative enthalpy and entropy values, determine how the process is affected after each of the following temperature or pressure changes. Consider that a more effective reaction produces more product or more product in a shorter amount of time.
Kp = 8×1015 Yes; the reaction is highly spontaneous at 298 K and almost no SO2 will remain at equilibrium. PSO2 = 5.0×10−7 atm
What substance is produced at the cathode during the electrolysis of a mixture of molten calcium bromide, CaBr2(l), and molten magnesium iodide, MgI2(l)? Assume standard conditions
Mg2++2e−→Mg
Which of the following processes most likely results in a decrease in entropy? 6H5OH(s) → C6H5OH(aq) LiCl(s) → Li+(aq) + Cl−(aq) MgSO4(s) → Mg2+(aq) + SO4 2−(aq) KBr(s) → K+(aq) + Br−(aq)
MgSO4(s) → Mg2+(aq) + SO4 2−(aq)
In the equation 8H+(aq) + MnO4 −(aq) + 5Fe2+(aq) →5Fe3+(aq) + Mn2+(aq) + 4H2O(l), the ____.
Mn is being reduced.
What is the shorthand notation that represents the following galvanic cell reaction? Ni(s) + Cu(NO3)2(aq) → Ni(NO3)2(aq) + Cu(s)
Ni(s) | Ni 2+(aq) || Cu2+(aq) | Cu(s)
Consider the following galvanic cell that uses the reaction 2Ag+(aq)+Ni(s)→2Ag(s)+Ni2+(aq) Identify the anode half-reaction. Identify the cathode half-reaction. Label the anode and cathode, indicate the direction of electron and ion flow, and identify the sign of each electrode.
Ni(s)→Ni2+(aq)+2e− Ag+(aq)+e−→Ag(s)
Write balanced equation for overall cell reactions of the following galvanic cell Fe(s)|Fe2+(aq)||O2(g)|H+(aq),H2O(l)|Pt(s)
O2(g)+4H+(aq)+2Fe(s)→2Fe2+(aq)+2H2O(l)
Write balanced equation for the cathode of the following galvanic cell Fe(s)|Fe2+(aq)||O2(g)|H+(aq),H2O(l)|Pt(s)
O2(g)+4H+(aq)+4e−→2H2O(l)
Given values of ΔG∘f at 25 ∘C for liquid ethanol (-174.9 kJ/mol) and gaseous ethanol (- 167.9 kJ/mol), calculate the vapor pressure of ethanol at 25 ∘C.
P = 0.059 atm
Use the data in Appendix B in the textbook to calculate the vapor pressure of hydrazine (N2H4) at 25 ∘C.
P = 1.7×10−2 atm
Consider the reaction Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s) at 45 ∘C , where [Fe2+]= 3.50 M and [Mg2+]= 0.310 M . What is the value for the reaction quotient, Q, for the cell? What is the value for the temperature, T, in kelvins? What is the value for n? Calculate the standard cell potential for Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s) What is the cell potential for the reaction Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s) at 45 ∘C when [Fe2+]= 3.50 M and [Mg2+]= 0.310 M .
Q = 8.86×10−2 T = 318 K n = 2 mol E∘ = 1.92 V E = 1.95 V
Consider a disordered crystal of monodeuteriomethane in which each tetrahedral CH3D molecule is oriented randomly in one of four possible ways. Use Boltzmann's formula to calculate the entropy of the disordered state of the crystal if the crystal contains 42 molecules Use Boltzmann's formula to calculate the entropy of the disordered state of the crystal if the crystal contains 420 molecules Use Boltzmann's formula to calculate the entropy of the disordered state of the crystal if the crystal contains 1 mol of molecules What is the entropy of the crystal if the C−D bond of each of the CH3D molecules points in the same direction? Crystal contains 42 molecules. What is the entropy of the crystal if the C−D bond of each of the CH3D molecules points in the same direction? Crystal contains 420 molecules. What is the entropy of the crystal if the C−D bond of each of the CH3D molecules points in the same direction? Crystal contains 1 mol of molecules.
S = 8.03×10−22 J/K S = 8.03×10−21 J/K S = 11.5 J/K S = 0 J/K S = 0 J/K S = 0 J/K
By what factor does the entropy increase for a collection of 100 molecules moved from 1×108 boxes to 1×109 boxes? For a move from 1×1020 to 1×1021 boxes?
Sf/Si = 1.13 Sf/Si = 1.05
Use the data in Appendix D to predict whether the following reactions can occur under standard-state conditions. Oxidation of Sn2+(aq) by Br2(aq) Reduction of Ni2+(aq) by Sn2+(aq) Oxidation of Ag(s) by Pb2+(aq) Reduction of I2(s) by H2SO3(aq)
Sn2+(aq) can be oxidized by Br2(aq) Ni2+(aq) cannot be redused by Sn2+(aq) Ag(s) cannot be oxidized by Pb2+(aq) I2(s) can be redused by H2SO3(aq)
Cd(s)+Sn2+(aq)→Cd2+(aq)+Sn(s) Write the cathode half-reaction.
Sn2+(aq)+2e−→Sn(s)
Elemental sulfur is formed by the reaction of zinc sulfide with oxygen: 2ZnS(s)+O2(g)→2ZnO(s)+2S(s) If ΔH∘= -289.0 kJ/mol and ΔS∘= -169.4 J/K , what is ΔStotal for this reaction? Is the reaction spontaneous under standard-state conditions at 25 ∘C? At what temperature, if any, will the reaction become nonspontaneous?
Stotal = 800.4 J/K yes T = 1706 K
Calculate the melting point of benzoic acid (C6H5CO2H), given the following data: ΔHfusion = 18.02 kJ/mol and ΔSfusion = 45.56 J/(mol⋅K)
T = 122.4 ∘C
Which process is spontaneous? Blowing up a balloon The crystallization of sugar from an unsaturated solution of sugar in water The separation of nitrogen gas from air Tarnishing silver
Tarnishing silver
Consider a system consisting of a cylinder with a movable piston containing 106 gas molecules at 298 K at a volume of 1 L. Consider the following descriptions of this system: A: Initial system, as stated in the problem statement. B: Starting from the initial system, the volume of the container is changed to 2 L and the temperature to 395 K. C: Starting from the initial system, a combination reaction occurs at constant volume and temperature. D: Starting from the initial system, the gas reacts completely to produce 107 gas molecules at 395 K in a volume of 2 L. E: Starting from the initial system, the temperature is changed to 395 K at constant volume. Arrange the descriptions in order of increasing number of microstates in the resulting system.
The same factors can be used on a macroscopic level to predict relative changes in entropy, for example, by examining a chemical equation for changes in physical states and number of moles of product and reactant particles.
Describe how the signs of ΔH and ΔS determine whether a reaction is spontaneous or nonspontaneous at constant temperature and pressure. Check all that apply. When ΔH and ΔS are both negative, reaction is spontaneous at low temperatures (if |ΔH|>|T⋅ΔS|) and nonspontaneous at high temperatures (if |ΔH|<|T⋅ΔS|) . When ΔH is positive and ΔS is negative, reaction is spontaneous at all temperatures. When ΔH and ΔS are both positive, reaction is spontaneous at high temperatures (if ΔH<T⋅ΔS) and nonspontaneous at low temperatures (if ΔH>T⋅ΔS) . When ΔH and ΔS are both negative, reaction is spontaneous at high temperatures (if |ΔH|<|T⋅ΔS|) and nonspontaneous at low temperatures (if |ΔH|>|T⋅ΔS|) . When ΔH is negative and ΔS is positive, reaction is spontaneous at all temperatures. When ΔH is negative and ΔS is positive, reaction is nonspontaneous at all temperatures. When ΔH is positive and ΔS is negative, reaction is nonspontaneous at all temperatures. When ΔH and ΔS are both positive, reaction is spontaneous at low temperatures (if ΔH>T⋅ΔS) and nonspontaneous at high temperatures (if ΔH<T⋅ΔS) .
When ΔH and ΔS are both negative, reaction is spontaneous at low temperatures (if |ΔH|>|T⋅ΔS|) and nonspontaneous at high temperatures (if |ΔH|<|T⋅ΔS|). When ΔH and ΔS are both positive, reaction is spontaneous at high temperatures (if ΔH<T⋅ΔS) and nonspontaneous at low temperatures (if ΔH>T⋅ΔS) . When ΔH is negative and ΔS is positive, reaction is spontaneous at all temperatures. When ΔH is positive and ΔS is negative, reaction is nonspontaneous at all temperatures.
Consider the reaction 2KClO3(s)→2KCl(s)+3O2(g) and the following table of values: Substance ΔG∘f (kJ/mol) KClO3(s) −296.3 KCl(s) −408.2 O2(g) 0 State whether it would be worthwhile to investigate finding a catalyst to use in this reaction under standard conditions and explain why.
Yes, because ΔG∘ is negative.
What overall reaction is most likely to occur when an aqueous solution of ZnI2 is placed in an electrolytic cell with inert electrodes? (E° for Zn2+/Zn = −0.76 V, E° for I2/I− = 0.54 V, E° for O2/H2O = 1.23 V, E° for H2O/H2 = −0.83 V)
Zn2+(aq) + 2I−(aq) →Zn(s) + I2(s)
An electrolytic cell is
a cell in which an electric current drives a nonspontaneous reaction
Which state has the higher entropy? a perfectly ordered crystal of solid nitrous oxide (N−N−O) a disordered crystal in which the molecules nitrous oxide (N−N−O) are oriented randomly
a disordered crystal in which the molecules nitrous oxide (N−N−O) are oriented randomly
The chemical system shown below is at equilibrium. Which change in conditions will not result in a spontaneous forward reaction? N2(g) + 3 H2(g) ↔ 2 NH3(g) Kp = 4 × 105
adding a catalyst
Predict whether the following reaction will occur: Fe(s)+Cu2+(aq)→Fe2+(aq)+Cu(s).
can occur
Predict whether the following reaction will occur: Ag(s)+Cu2+(aq)→Cu(s)+2Ag+(aq).
can't occur
For a spontaneous process
energy is conserved and the entropy of the system and surroundings increases.
At 25°C, ΔH° = 1.895 kJ and ΔS° = -3.363 J/K for the transition C(graphite) → C(diamond) Based on these data
graphite cannot be converted to diamond at 1 atm pressure.
Consider the galvanic cell, Pt(s) | H2(1 atm) | H+(1 M) || Cl-(1 M) | Hg2Cl2(s) | Hg(l) Which one of the following changes to the cell would cause the cell potential to increase (i.e., become more positive)?
increase the pH
How many kilograms of aluminum can be produced in 6.87 h by passing a constant current of 1.46×105A through a molten mixture of aluminum oxide and cryolite?
m = 337 kg
How many grams of silver will be obtained when an aqueous silver nitrate solution is electrolyzed for 15.5 min with a constant current of 2.34 A ?
mAg = 2.43 g
Consider the following gas-phase reaction of A2 (red) and B2 (blue) molecules: A2+B2⇌2AB ΔG∘ = 35 kJ Which of the reaction mixtures has the largest ΔG of reaction? Which has the smallest ΔG? If the partial pressure of each reactant and product in reaction mixture 1 is equal to 1 atm, what is the value of ΔG for the reaction in mixture 1?
mixture 3 mixture 2 ΔG = 35 kJ/mol
Is it possible to synthesize acetylene from solid graphite and gaseous H2 at 25 ∘C and 1 atm pressure?
no
The following data apply to the vaporization of mercury: ΔHvap = 59.11 kJ/mol, ΔSvap = 93.9 J/(K⋅mol). Does mercury boil at 325 ∘C and 1 atm pressure? What is the normal boiling point of mercury?
no Tboil = 356 ∘C
Which forward reaction is a nonspontaneous process?
none of the above
Which of the following processes are spontaneous, and which are nonspontaneous? Freezing of water at 2 ∘C Corrosion of iron metal Expansion of a gas to fill the available volume Separation of an unsaturated aqueous solution of potassium chloride into solid KCl and liquid water
nonspontaneous spontaneous spontaneous nonspontaneous
A particular solvent with ΔS∘vap=112.9J/(K⋅mol) and ΔH∘vap=38.0kJ/mol is being considered for an experiment. In the experiment, which is to be run at 75 ∘C, the solvent must not boil. Based on the overall entropy change associated with the vaporization reaction, would this solvent be suitable and why or why not? The solvent would be suitable because ΔSuniv>0. not be suitable because ΔSuniv>0. be suitable because ΔSuniv<0. not be suitable because ΔSuniv<0.
not be suitable because ΔSuniv>0.
Assign an oxidation number to each atom in the following compound: SnCl4. Assign an oxidation number to each atom in the following compound: CrO3. Assign an oxidation number to each atom in the following compound: K2CrO4. Assign an oxidation number to each atom in the following compound: V2O3. Assign an oxidation number to each atom in the following compound: H2SO3. Assign an oxidation number to each atom in the following compound: FeSO4
oxidation numbers of Sn, Cl = +4,-1 oxidation numbers of Cr, O = +6,-2 oxidation numbers of K, Cr, O = +1,+6,-2 oxidation numbers of V, O = +3,-2 oxidation numbers of H, S, O = +1,+4,-2 oxidation numbers of Fe, S, O = +2,+6,-2
The following cell has a potential of 0.35 V at 25 ∘C: Pt(s)|H2(1atm)∣∣H+(?M)∥∥Ni2+(1M)|Ni(s) What is the pH of the solution in the anode compartment?
pH = 10
Calculate the equilibrium partial pressure of magnesium vapor above solid magnesium at 25 ∘C if ΔG∘f for gaseous magnesium is 112.5 kJ/mol at 25 ∘C.
pMg = 1.9×10−20 atm
Which state has the higher entropy? quartz crystal quartz glass
quartz glass
Which of the following processes are spontaneous? Which are non-spontaneous? Diffusion of perfume molecules from one side of a room to the other Heat flow from a cold object to a hot object Decomposition of rust (Fe2O3⋅H2O) to iron metal, oxygen, and water Decomposition of solid CaCO3 to solid CaO and gaseous CO2 at 25 ∘C and 1 atm pressure (Kp=1.4×10−23)
spontaneous non-spontaneous non-spontaneous non-spontaneous
Is the reaction spontaneous in the forward or the reverse direction under these conditions?
spontaneous in the reverse direction
According to the second law of thermodynamics, all reactions proceed spontaneously in the direction that increases the entropy of the
system + surroundings
How many hours are required to produce 1050 kg of sodium by the electrolysis of molten NaCl with a constant current of 3.10×104 A ? How many liters of Cl2 at STP will be obtained as a by-product?
t = 39.5 h VCl2 = 5.12×105 L
A layer of silver is electroplated on a coffee server using a constant current of 0.183 A . How much time is required to deposit 3.19 g of silver?
t = 4.33 h
Which of the three laws of thermodynamics provides a criterion for spontaneity?
the second law of thermodynamics
Predict which of the following compounds follow Trouton's rule. toluene n-propanol octane benzene ammonia carbon tetrachloride
toluene octane benzene carbon tetrachloride
Might this reaction be used for the synthesis of acetylene (HC≡HC, or C2H2)
yes
What is the change in the cell voltage on decreasing the ion concentrations in the anode compartment by a factor of 10?
ΔE = 3.0×10−2 V
What is the change in the cell voltage on decreasing the ion concentrations in the cathode compartment by a factor of 10?
ΔE = −9.5×10−2 V
At 25 ∘C the reaction from Part A has a composition as shown in the table below. Substance Pressure (atm) C2H2(g) 4.25 H2(g) 3.85 C2H6(g) 3.25×10−2 What is the free energy change, ΔG, in kilojoules for the reaction under these conditions?
ΔG = -261 kJ
The silver oxide-zinc battery used in watches delivers a voltage of 1.60 V. Calculate the free-energy change (in kilojoules) for the cell reaction Zn(s)+Ag2O(s)→ZnO(s)+2Ag(s)
ΔG = -309 kJ
Given that for the vaporization of benzene ΔHvap = 30.7 kJ/mol and ΔSvap = 87.0 J/(K⋅mol), calculate ΔG for the vaporization of benzene at the following temperatures. 72 ∘C 80 ∘C 86 ∘C Predict whether benzene will boil at each of these temperatures and 1 atm pressure. 72 ∘C 80 ∘C 86 ∘C
ΔG = 0.7 kJ/mol ΔG = 0 kJ/mol ΔG = -0.5 kJ/mol will not boil will boil will boil
Use the data in Appendix B in the textbook to calculate ΔG for the decomposition of nitrosyl chloride at 25 ∘C when the partial pressures are 10.0 atm of NOCl, 3.00×10−3 atm of NO, and 3.00×10−3 atm of Cl2. 2NO(g)+Cl2(g)→2NOCl(g)
ΔG = 11.6 kJ⋅mol−1
What is the relationship between ΔG and the ΔG°F for the reaction below? MgF2(s) → Mg2+(aq) + 2 F-(aq)
ΔG = {ΔG°f [Mg2+ (aq)] + 2 ΔG°f [F- (aq)] - ΔG°f [MgF2 (s)]} + RT ln ([Mg2+] [F-])2)
Why is the sign of ΔG rather than the sign of ΔStotal generally used to determine the spontaneity of a chemical reaction?
ΔG involves thermodynamic functions of the system only.
Free-energy change, ΔG∘, is related to cell potential, E∘, by the equation ΔG∘=−nFE∘ where n is the number of moles of electrons transferred and F=96,500C/(mol e−) is the Faraday constant. When E∘ is measured in volts, ΔG∘ must be in joules since 1 J=1 C⋅V. Calculate the standard free-energy change at 25 ∘C for the following reaction: Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s) Calculate the standard cell potential at 25 ∘C for the reaction X(s)+2Y+(aq)→X2+(aq)+2Y(s) where ΔH∘ = -573 kJ and ΔS∘ = -147 J/K .
ΔG∘ = −3.71×105 J E∘ = 2.74 V
Using values of ΔG∘ in Appendix B in the textbook, calculate the standard free-energy change for the reaction of calcium carbide (CaC2) with water. CaC2(s)+2H2O(aq)→C2H2(g)+Ca(OH)2(s)
ΔG∘ = -148.4 kJ
Ethanol is manufactured in industry by the hydration of ethylene: CH2¯¯¯¯¯¯¯¯CH2(g)+H2O(l)→CH3CH2OH(l) Using the data in Appendix B in the textbook, calculate ΔG∘. Why is this reaction spontaneous at 25 ∘C? Why does this reaction become nonspontaneous at higher temperatures? Estimate the temperature at which the reaction becomes nonspontaneous.
ΔG∘ = -6.1 kJ Because ΔG∘ is negative. Because ΔS∘ is negative. T = 72 ∘C
Use the standard free energies of formation in Appendix B in the textbook to calculate ΔG∘ at 25 ∘C for each reaction. N2(g)+2O2(g)→2NO2(g) 2KClO3(s)→2KCl(s)+3O2(g) CH3CH2OH(l)+O2(g)→CH3CO2H(l)+H2O(l)
ΔG∘ = 102.6 kJ ΔG∘ = -224.4 kJ ΔG∘ = -452 kJ
Consider the thermal decomposition of calcium carbonate: CaCO3(s)→CaO(s)+CO2(g) Use the data in Appendix B in the textbook to calculate the standard free-energy change for this reaction at 25 ∘C. Will a mixture of solid CaCO3, solid CaO, and gaseous CO2 at 1 atm pressure react spontaneously at 25 ∘C to produce more CaO and CO2? Assuming that ΔH∘ and ΔS∘ are independent of temperature, estimate the temperature at which the reaction becomes spontaneous.
ΔG∘ = 131.5 kJ no T = 847 ∘C
Use the values of ΔG∘f in Appendix B in the textbook to calculate the standard free-energy change for the synthesis of hydrazine from nitrogen and hydrogen. N2(g)+H2(g)→N2H4(l) Is it possible to synthesize hydrazine from gaseous N2 and H2, each at 25 ∘C and 1 atm pressure?
ΔG∘ = 149.2 kJ no
What is the relationship between the standard free-energy change, ΔG∘ , for a reaction and the equilibrium constant,K? What is the sign of ΔG∘ when K>1? What is the sign of ΔG∘ when K=1? What is the sign of ΔG∘ when K<1?
ΔG∘=−RTlnK ΔG∘ is negative. ΔG∘=0 ΔG∘ is positive.
Elemental carbon usually exists in one of two forms: graphite or diamond. It is generally believed that diamonds last forever. The table shows the standard enthalpy of formation (ΔH∘f) and the standard molar entropy (S∘) values for diamond and graphite. What is the standard Gibbs free energy for the transformation of diamond to graphite at 298 K? Cdiamond→Cgraphite What can be said about the spontaneity of this reaction? Cdiamond→Cgraphite
ΔG∘rxn = -2.90 kJ The forward reaction is spontaneous at 298 K.
The chemical reaction that causes chromium to corrode in air is given by 4Cr+3O2→2Cr2O3 in which at 298 K ΔH∘rxn = −2256 kJ ΔS∘rxn = −549.1 J/K What is the standard Gibbs free energy for this reaction? Assume the commonly used standard reference temperature of 298 K. What is the Gibbs free energy for this reaction at 4717 K ? Assume that ΔH and ΔS do not change with temperature. At what temperature Teq do the forward and reverse corrosion reactions occur in equilibrium?
ΔG∘rxn = -2092 kJ ΔGrxn = 334 kJ Teq = 4109 K
Consider the reaction 2A(g) ↔ A2(g). The following pictures represent two possible initial states and the equilibrium state of the system. What are the signs (+ or -) of ΔH, ΔS, and ΔG when the system spontaneously goes from initial state 1 to the equilibrium state?
ΔH = -, ΔS = -, ΔG = -
Consider a twofold expansion of 1 mol of an ideal gas at 0 ∘C in the isolated system shown in the following figure. What is the value of ΔH for the process? What is the value of ΔS for the process? What is the value of ΔG for the process?
ΔH = 0 kJ⋅mol−1 ΔS = 5.76 J⋅K−1 ΔG = -1570 J
In figure (1) below oxygen molecules, represented by unshaded spheres, and chlorine molecules, represented by shaded spheres, are in separate compartments. Figure (2) shows the equilibrium state of the system after the stopcock separating the two compartments is opened. Assuming the oxygen and the chlorine behave as ideal gases, what are the signs (+, -, or 0) of ΔH, ΔS, and ΔG for this process?
ΔH = 0, ΔS = +, ΔG = -
Which combination indicates a reaction at equilibrium at the given temperature?
ΔH = −45 kJ, ΔS = −151 J/K, temperature = 298 K
Sodium reacts violently with water according to the equation: 2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g) The resulting solution has a higher temperature than the water prior to the addition of sodium. What are the signs of ΔH∘ and ΔS∘ for this reaction?
ΔH° is negative and ΔS° is positive.
Use the data in Appendix B in the textbook to calculate the following quantities. ΔH∘ for the following reaction N2(g)+2O2(g)→2NO2(g) ΔS∘ for this reaction. From the values of ΔH∘ and ΔS∘, calculate ΔG∘ at 25 ∘C. Predict whether this reaction is spontaneous under standard-state conditions. ΔH∘ for the following reaction 2KClO3(s)→2KCl(s)+3O2(g) ΔS∘ for this reaction. From the values of ΔH∘ and ΔS∘, calculate ΔG∘ at 25 ∘C. Predict whether this reaction is spontaneous under standard-state conditions. ΔH∘ for the following reaction CH3CH2OH(l)+O2(g)→CH3CO2H(l)+H2O(l) ΔS∘ for this reaction. From the values of ΔH∘ and ΔS∘, calculate ΔG∘ at 25 ∘C. Predict whether this reaction is spontaneous under standard-state conditions.
ΔH∘ = 66.4 kJ ΔS∘ = -121.5 J/K ΔG∘ = 102.6 kJ nonspontaneous under standard-state conditions ΔH∘ = -77.6 kJ ΔS∘ = 494.0 J/K ΔG∘ = -224.8 kJ spontaneous under standard-state conditions ΔH∘ = -492.6 kJ ΔS∘ = -136.1 J/K ΔG∘ = -452.0 kJ spontaneous under standard-state conditions
Predict the sign of ΔS in the system for each of the following processes. H2O(g)→H2O(l) (formation of rain droplets) I2(g)→2I(g) CaCO3(s)→CaO(s)+CO2(g) Ag+(aq)+Br−(aq)→AgBr(s) Deposition of frost on a cold morning, H2O(g)→H2O(s)
ΔS < 0 ΔS > 0 ΔS > 0 ΔS < 0 ΔS < 0
A gaseous system undergoes a change in temperature and volume. What is the entropy change for a particle in this system if the final number of microstates is 0.704 times that of the initial number of microstates?
ΔS = −4.84×10−24 J/(K⋅particle)
What is the entropy change when the volume of 1.8 g of O2 increases from 2.0 L to 3.8 L at a constant temperature of 75 ∘C? Assume that O2 behaves as an ideal gas.
ΔS = 0.30 J/K
The entropy change associated with the expansion of one mole of an ideal gas from an initial volume of Vi to a final volume of Vf at constant temperature is given by the equation, ΔS = R ln (Vf/Vi). What is the entropy change associated with the expansion of three moles of an ideal gas from an initial volume of Vi to a final volume of Vf at constant temperature?
ΔS = 3 mol × R ln (Vf/Vi)
Predict the sign of ΔS for each process. Freezing of water at 2 °C Corrosion of iron metal Expansion of a gas to fill the available volume Separation of an unsaturated aqueous solution of potassium chloride into solid KCl and liquid water
ΔS<0 ΔS<0 ΔS>0 ΔS<0
For the vaporization of benzene, ΔHvap = 30.7 kJ/mol and ΔSvap = 87.0 J/(K⋅mol). Calculate ΔSsurr and ΔStotal at 72 ∘C. Calculate ΔSsurr and ΔStotal at 80 ∘C. Calculate ΔSsurr and ΔStotal at 95 ∘C. Does benzene boil at 72 ∘C and 1 atm pressure? Calculate the normal boiling point of benzene.
ΔSsurr = -89.0 J/K ΔStotal = -2.0J/K ΔSsurr = -87.0 J/K ΔStotal = 0 J/K ΔSsurr = -83.4 J/K ΔStotal = 3.6 J/K no Tbp = 80 ∘C
Elemental mercury can be produced from its oxide: 2HgO(s)→2Hg(l)+O2(g) Use data in Appendix B to calculate ΔSsys for this reaction. Use data in Appendix B to calculate ΔSsurr for this reaction. Use data in Appendix B to calculate ΔStotal for this reaction. Is the reaction spontaneous under standard - state conditions at 25∘C? Estimate the temperature at which the reaction will become spontaneous.
ΔSsys = 216.4 JK ΔSsurr = -609.4 JK ΔStotal = -393.0 JK no T = 839.2 K
By determining the sign of ΔStotal , show whether the decomposition of calcium carbonate is spontaneous under standard-state conditions at 25 ∘C. CaCO3(s)→CaO(s)+CO2(g) Use data in Appendix B to calculate ΔStotal under standard-state condition. Is the decomposition of calcium carbonate spontaneous under standard-state conditions?
ΔStotal = -441 JK no
Calculate the standard-state entropy for the following reaction: 1 Al2O3(s) + 3 H2(g) ⟶ 2 Al(s) + 3 H2O(l) (If applicable, coefficients of one have been included for clarity.) The standard entropy values are given in the table.
ΔS∘ = 179 JK
Use the standard molar entropies in Appendix B in the textbook to calculate the standard entropy of reaction for the oxidation of graphite to carbon dioxide: C(s)+O2(g)→CO2(g)
ΔS∘ = 2.9 J⋅K−1
Use the standard molar entropies in Appendix B in the textbook to calculate ΔS∘ at 25 ∘C for each of the following reactions. Account for the sign of the entropy change in each case. 2H2O2(l)→2H2O(l)+O2(g) Account for the sign of the entropy change. 2SO2(g)+O2(g)→2SO3(g) Account for the sign of the entropy change. 2O3(g)→3O2(g) Account for the sign of the entropy change. 4Al(s)+3O2(g)→2Al2O3(s) Account for the sign of the entropy change.
ΔS∘ = 125 J⋅K−1 because moles of gas increase ΔS∘ = -188.0 J⋅K−1 because moles of gas decrease ΔS∘ = 137.4 J⋅K−1 because moles of gas increase ΔS∘ = -626.4 J⋅K−1 because moles of gas decrease
Nitric oxides, NO and NO2, contribute to air pollution, acid rain, and the depletion of the ozone layer. After NO forms in the combustion chamber of an automobile engine, it reacts further with oxygen to form NO2. The reaction is given by 2NO(g)+O2(g)→2NO2(g) The following table gives some entropy values: Calculate ΔS∘rxn for the reaction 2NO(g)+O2(g)→2NO2(g) A negative change in entropy indicates that
ΔS∘rxn = -146.8 JK the products have a smaller number of available energy microstates than the reactants.
What are the signs of ΔH for the spontaneous condensation of a vapor to a liquid? What are the signs of ΔS for the spontaneous condensation of a vapor to a liquid? What are the signs of ΔG for the spontaneous condensation of a vapor to a liquid?
− − -
What is the standard entropy change for the reaction 2SO2(g) + O2(g) → 2SO3(g)? (S° of SO2(g) = 248.1 J/(mol·K); S° of O2(g) = 205.0 J/(mol·K); S° of SO3(g) = 256.6 J/( K·mol))
−188.0 J/K
The standard cell potential at 25 ∘C is 1.56 V for the reaction 2Ag+(aq)+Zn(s)→2AgS(s)+Zn2+(aq) What is the standard free-energy change for this reaction at 25 ∘C?
−3.01×105 J
Calculate the standard free-energy change for the reaction CH4(g) + 4Cl2(g) → CCl4(l) + 4HCl(g) (ΔG : −50.8 kJ/mol (CH4), −65.3 kJ/mol (CCl4), −95.3 kJ/mol (HCl)).
−396 kJ
