Chem 218
If the molar heat of vaporization of ethanol is 38.6 kJ/mol and its boiling point is 78.3°C, what is the value of ΔSvap for ethanol?
+110 J/K⋅mol 38.6/(78.3+273.15)x1000=109.8 = +110 J/K*mol
Ksp for iron(III) hydroxide [Fe(OH)3] is equal to 1.1 x 10-36 at 25oC. Determine ΔGo (in kJ/mol) at 25oC for the reaction represented by the equation Fe(OH)3 (s) ⇌ Fe3+ (aq) + 3OH- (aq).
+205 kJ/mol Reason: ΔG = -8.314 x 298 x ln(1.1 x 10-36) = 217,000 J/mol = 217 kJ/mol
A reaction is spontaneous at room temperature, but when cooled, it becomes nonspontaneous at 279 K. If ΔH for the reaction is +102.4 kJ/mol, what is the entropy change of the reaction?
+367 J/K⋅mol Reason: ΔG = ΔH - TΔS ΔG = 102.4 kJ/mol - (279 K)ΔS = 0 ΔS = 102.4 kJ/mol279 K ΔS = +0.367 kJ/K⋅mol = +367 J/K⋅mol
Use the information below to solve for ΔG°rxn for the simple reaction A → 2B. 'substance ΔG°f (kJ/mol) A. -10 B. -20
-30 kJ Reason: ΔG°rxn = 2(-20) - (-10) = -30
The reaction to form BrF3 (shown below) has a ΔG° of -459 kJ/mol. If the initial partial pressures are PF2 = 1.75 atm and PBrF3 = 0.187 atm and the reaction temperature is 300 K, what is ΔG for the reaction? Br2(l) + 3F2(g) → 2BrF3(g)
-472 kJ/mol Reason: ΔG = ΔG° + RT ln Q Q = (PBrF3)2(PF2)3PBrF32PF23 = (0.187 atm)2(1.75 atm)30.187 atm21.75 atm3 ΔG = (-459 kJmolkJmol) + (.008314 kJ)(300 K) ln (.00652) ΔG = -472 kJ/mol
Which of the following options correctly explain why the equation S = k ln W is rarely used to calculate the change in entropy of a system? Select all that apply
-Tabulated standard entropy values are routinely used to calculate entropy changes. -It is difficult to determine the number of possible arrangements (W) for a macroscopic system. -Absolute entropy can be measured using calorimetric methods.
In which of the following options does the first species of each pair have a greater standard entropy? Select all that apply. Multiple select question. A substance in the liquid phase vs. the same substance in the gas phase An allotrope with fewer atoms vs. an allotrope with more atoms A more complex substance vs. a simpler substance in the same phase, if their molar masses are similar A larger monatomic substance vs. a smaller one
A more complex substance vs. a simpler substance in the same phase, if their molar masses are similar A larger monatomic substance vs. a smaller one
The freezing of water is spontaneous at temperatures below 0 C, although the process results in a decrease in the entropy of the system: H2O(l) → H2O(s); ΔSsys = -22 J/K Which of the following is the best explanation for the way in which this process obeys the second law of thermodynamics?
Freezing is exothermic; the surroundings increase in entropy. Reason: The addition of heat to the surroundings causes a much greater increase in entropy when the temperature is low (S = q/T). This is why water freezes only at low temperatures.
Which of the following options correctly reflect the relationships between ΔSsurr, ΔHsys, and T? Select all that apply.
If ΔHsys is negative, ΔSsurr will be positive. ΔSsurr is inversely proportional to temperature.
Based on the equation ΔG = ΔG° + RT ln(Q), match each range of Q values to the effect it has on the spontaneity of the reaction. Instructions Q=1 Q<1 Q>1
Q=1 There will be no change in spontaneity from standard conditions. Q<1 The forward reaction will be more favored and the reverse reaction less favored than at standard conditions. Q>1 The reverse reaction will be more favored and the forward reaction less favored than at standard conditions.
The reaction to form NH3 (shown below) has a ΔG° of -33.0 kJ/mol. If the partial pressures are 1.0 atm for N2, 1.5 atm H2, and 3.0 atm NH3 what is ΔG for the reaction? (T = 25oC) N2(g) + 3H2(g) → 2NH3(g)
Reason: ΔG = ΔG° + RT ln Q Q = (PNH3)2(PN2)(PH2)3PNH32PN2PH23 = (3.0 atm)2(1.0 atm)(1.5 atm)33.0 atm21.0 atm1.5 atm3 ΔG = (−33.0 kJmol)-33.0 kJmol + (8.314 × 10−3 kJmol⋅K)8.314 × 10-3 kJmol⋅K(298 K) ln (2.67) ΔG = -33.0 kJ/mol + 2.43 kJ/mol = -30.6 kJ/mol
If the molar heat of vaporization of carbon tetrachloride is 32.54 kJ/mol and its normal boiling point is 76.7°C, what is the value of ΔSvap (in J/K⋅mol) for CCl4?
Reason: ΔG = ΔH - TΔS ΔG = 0 at equilibrium 0 = 32.54 kJ/mol - (349.9 K)ΔS ΔS = (32.54 × 103 J/mol)/(349.9 K)= K = 93.00 J/K⋅mol 32.54/(76.7+273.15)x1000=93J/K*mol
The formation of water from its elements is spontaneous and highly exothermic, although the reaction results in a large decrease in the entropy of the system: 2H2(g) + O2(g) → 2H2O(ℓ) ΔSsys = -327 J/K Which of the following is the best explanation for the way in which this process obeys the second law of thermodynamics?
The reaction is highly exothermic; the surroundings increase in entropy. Reason: The addition of heat to the surroundings causes a greater increase in its entropy (S = q/T), making ΔSuniv > 0.
Which of the following conditions are specified by standard state conditions? Select all that apply.
The standard state of an element is its most stable allotropic form at standard state temperature and pressure. Solutions are at a concentration of 1 M. Gases are at a pressure of 1 atm.
The second law of thermodynamics states that the total _____ of the universe will _____ for any spontaneous process.
entropy; increase
Entropy depends on the number of energetically _____ states that a system can be arranged in. The greater the number of these states, the _____ the entropy of the system.
equivalent, higher
The larger the equilibrium constant K for a reaction, the more _____ the value of ΔGo and the more the _____ are favored at equilibrium.
negative; products Reason: If the value of K for a reaction is large, it means that the reaction favors the products strongly. The reaction is spontaneous in the forward direction, and the value of ΔGo will be negative.
Match each thermodynamic quantity with the information it provides about a given reaction. Instructions
ΔGo > 0 Reactants are favored at equilibrium. Reactants are favored at equilibrium. ΔG < 0 , Reaction will occur spontaneously. Reaction will occur spontaneously. ΔG > 0 , Reaction will be nonspontaneous. Reaction will be nonspontaneous. ΔGo < 0 Products are favored at equilibrium. Products are favored at equilibrium.
When a reaction reaches equilibrium, large amounts of the products are present and very few reactants remain. Which of the following statements must be true of this reaction at equilibrium? Select all that apply.
ΔG° < 0 ΔG = 0 K > 1
Which of the following correctly describe the standard free-energy change of a reaction ΔG°rxn? Select all that apply.
ΔG°rxn, like ΔH°rxn, can be calculated from tabulated values. ΔG°rxn = ΣnΔG°f(products) - ΣmΔG°f(reactants)
Entropy _____ as the number of energetically equivalent states of a system increases.
Increases
Select all that apply Which of the following options correctly describe entropy? Select all that apply. Multiple select question. -Any process that causes an increase in the entropy of a system will be spontaneous. -Entropy is a measure of the energy dispersal of a system. -Entropy is another term for kinetic energy or energy of movement. -The greater the volume a system occupies, the greater the entropy of the system. -The symbol for entropy is E.
-Entropy is a measure of the energy dispersal of a system. -The greater the volume a system occupies, the greater the entropy of the system
Which of the following statements correctly describe the general trends in standard entropy? Select all that apply. Multiple select question. For two monatomic species, the one with the larger molar mass will have a higher standard entropy. The solid phase of a given compound or element has a higher standard entropy than its liquid phase. A substance with a more complex structure will have a lower standard entropy than a simpler substance with a similar molar mass in the same phase. For elements with two allotropic forms, the one that is more mobile will have a greater value for standard entropy.
-For two monatomic species, the one with the larger molar mass will have a higher standard entropy. -For elements with two allotropic forms, the one that is more mobile will have a greater value for standard entropy.
Which statements correctly describe the entropy changes that occur when an ionic solid dissolves in water? Select all that apply. Multiple select question. The dissociation of an ionic solute in water causes the entropy of the solute to increase. The hydration of highly charged ions generally results in a decrease in the entropy of the system. The mobility of H2O molecules in such a solution is reduced since they are arranged in a specific way around the dissolved ions. The overall entropy of a system always increases when a substance dissolves, irrespective of the charges on the ions.
-The dissociation of an ionic solute in water causes the entropy of the solute to increase. -The hydration of highly charged ions generally results in a decrease in the entropy of the system. -The mobility of H2O molecules in such a solution is reduced since they are arranged in a specific way around the dissolved ions.
Which of the following statements correctly explain the increase in entropy that occurs when a substance changes from a solid to a liquid, or from a liquid to a gas? Select all that apply.
-The freedom of movement of the particles increases in the change solid → liquid → gas. -The energy of the particles increases during these phase changes.
Select the phase change that will have the most dramatic increase in entropy, and select the statement that best explains why. Multiple select question. The mobility of the particles increases much more when this phase change occurs. Vaporization of a substance The complexity of the system increases much more during this phase change. This phase change results in a decrease in the number of possible arrangements. Melting of a substance
-The mobility of the particles increases much more when this phase change occurs. -Vaporization of a substance
Which of the following statements correctly describe the parts of the universe? Select all that apply. -The universe is everything except the process under investigation. -The system in a chemical reaction includes the products and reactants. -The surroundings is the area currently being investigated. -The system and surrounding combined make up the universe.
-The system in a chemical reaction includes the products and reactants. -The system and surrounding combined make up the universe.
Using the data provided in the table, calculate the equilibrium constant KP at 25oC for the reaction 2O3 (g) ⇌ 3O2 (g). Substance ΔGof (kJ/mol) O3 (g) 163.4 O2 (g) 0
Reason: ΔGorxn = 3(0) - 2(163.4) = -326.8 kJ/mol ln K = -ΔGoRTΔGoRT = -−326.8x10008.314x298-326.8x10008.314x298 = 132 K = e132 = 2.1 x 1057
Which equation would be used to calculate ΔG°rxn for the reaction 2A + B → 3C + D?
3(40) - 20 - 2(10) + 5 Reason: ΔG°rxn = ΣmΔG°products - ΣnΔG°reactants = [3(40) + (-20)] - [2(10) + (-5)] = [3(40) - 20] - [2(10) - 5] = 3(40) - 20 - 2(10) + 5
Which of the following is an application of the second law of thermodynamics?
A gas expands because matter tends to spread out.
When a reaction is at equilibrium, the reaction quotient Q is always equal to and ΔG is equal to
K or equilibrium constant Blank 2: 0 or zero
Which of the following describes the most probable state of a system of gas molecules arranged in a container?
The molecules will be evenly distributed throughout the container.
is the number of molecules in a system, N, related to the number of possible arrangements of the system, W?
W = X^N
The third law of thermodynamics states that the entropy of a perfect crystal at 0 K is 0. This allows for the calculation of ______ entropies unlike standard ______ of formation, which are derived using an arbitrary reference.
absolute, enthalpies
Thermodynamics tells us whether a reaction is spontaneous, but it does not tell us how BLANK it will occur.
fast, quickly, slowly, rapidly, or speedily
Rank the following compounds in order of decreasing standard molar entropies. Place the compound with the highest entropy at the top of the list.
-C3H8 (g) -CH4 (g) -CH4 (l)
Which of the following symbols denotes a standard free-energy change of reaction?
ΔG°rxn
Calculate ΔSuniv and identify the process CO2(g) → CO2(aq) as spontaneous or nonspontaneous at equilibrium at 25°C. Use the values provided in the table below. Substance So (J/mol⋅K) ΔHo (kJ/mol) CO2(g) 213.6 -393.5 CO2(aq) 121.3 -412.9
ΔSuniv = -27.2 J/mol⋅K The reaction is nonspontaneous at this temperature.
Which statement best describes standard entropies?
Absolute entropies determined at 1 atm of pressure
calculate ΔSsys we may use tables of entropies instead of the difficult task of determining changes to W, the number of possible equivalent-energy arrangements.
Standard
Which of the following values must be known in order to calculate the change in Gibbs free energy under standard conditions? Select all that apply.
T ΔSsys ΔHsys
As the reaction quotient Q increases, what is the effect on the spontaneity of the reaction?
The reaction becomes less spontaneous.
Calculate the entropy change of the surroundings in J/K⋅mol when 30 kJ of heat is released by the system at 27 C.
+100 This is the result of -(−30,000J/300K)
Which statement correctly describes the relationship between the entropy and spontaneity of a process?
A reaction/process will be spontaneous if ΔSsys > 0 and ΔSsurr > 0.
Which of the following options correctly describe the Gibbs free-energy change (ΔG) of a system? Select all that apply.
A ΔG value of zero indicates a process at equilibrium. ΔG is a measure of the spontaneity of a process.
A system is in a state of when ΔSuniv = 0.
Equilibrium
True or false: A negative ΔH value means that a process will necessarily be spontaneous.
False
The Gibbs energy change (symbolized by Δ) is a measure of the spontaneity of a process and of the useful energy available from it.
Free; G
Match each state of matter with the appropriate characteristics at standard state. Gases . Solutions Solids or liquids
Gases Pressure of 1 atm solutions 1 M concentration solids or liquids Pure substance in its most stable form
In which of the following options will the system exhibit an increase in standard entropy? Select all that apply. Multiple select question. Forming sucrose crystals from a supersaturated solution Heating H2 gas from 60°C to 80°C Subliming dry ice Condensing water vapor
Heating H2 gas from 60°C to 80°C Subliming dry ice
The state with the largest number of possible arrangements is called the most probable. , state.
Probable
Match each symbol in the equation S = k ln W correctly with its meaning.
S matches, entropy k matches, Boltzmann constant W matches, number of energetically equivalent states
The standard free-energy change for a reaction is the free-energy change for the reaction under -state conditions, which assumes that all gases are at atm of pressure and all solutions have a concentration of M.
Standard; 1; 1
Which of the following is a correct statement of the third law of thermodynamics?
The entropy of a perfect crystalline substance is 0 at 0 K.
What effect does increasing the temperature of a gas have on its entropy, and why? Multiple select question. The entropy of a system increases as temperature increases. As the temperature of a system is increased, fewer possible arrangements are available for the particles. As the temperature of a system is increased, all types of kinetic energies increase. The entropy of a system decreases as temperature increases.
The entropy of a system increases as temperature increases. As the temperature of a system is increased, all types of kinetic energies increase.
For a reaction with ΔH = -84.3 kJ/mol and ΔS = -412 J/K⋅mol, at what conditions will the reaction be spontaneous?
The reaction must be cooled to below 205 K. T= ΔH/ΔS (-84.3 kJ/mol)/[(-412 J/K⋅mol)(1kJ/1000J)]= 205K
The entropy change for a process is calculated from the equation ΔS = S _____ - S _____.
final, initial
In many biochemical coupled reactions, thermodynamically unfavorable reactions are driven by the ______ provided by a favorable reaction.
free energy
The objects and species being investigated are called the BLANK. Everything else is called the BLANK . Together, they make up the BLANK
system; surroundings; universe
The third law of thermodynamics establishes a zero point for entropy, which enables us to experimentally determine the _____ entropies of substances.
Absolute
Which of the following is the equation for the Gibbs free energy of a process occurring at a constant temperature?
ΔGsys = ΔHsys - TΔSsys
Which of the following options correctly defines the standard free energy of formation for a substance?
The free-energy change that occurs when 1 mole of the compound is formed from its elements in their standard states
When ΔG (the change in free energy) for a reaction is less than zero (negative), the reaction is _____ and the entropy change (ΔS) for the universe is _____.
spontaneous; positive
Match the relative values of Q and K with the associated value of ΔG. Instructions Q < K Q<K drop zone empty. Q > K Q>K drop zone empty. Q = K
ΔG < 0 ΔG > 0 ΔG = 0
If a given process proceeds spontaneously toward the products, the value of the reaction quotient Q is _____ the equilibrium constant K and ΔG for the reaction will be _____.
less than; negative
True or false: A reaction with a positive ΔSuniv may occur quickly or slowly.
True Reason: Correct. A positive value for ΔSuniv indicates that the reaction is spontaneous, but gives no information about the rate of the reaction.
Unlike enthalpies of formation, which are relative to an arbitrary reference, true values of entropies can be found. These values are called BLANK entropies.
Absolute
The equilibrium constant for the reaction shown below is 7 x 10-84. What information does this provide about the reaction? Select all that apply. H2(g) + I2(g) ⇌ 2HI(g)
At equilibrium the reaction mixture consists mostly of H2(g) and I2(g). ΔGo is positive for this reaction.
In which cases do the substance(s) on the left have a higher entropy than the substance(s) on the right?
C3H8(g) vs. C2H6(g) 2NO2(g) vs. N2O4(g)
The combustion of glucose, represented by the equation C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(g) is an exothermic reaction. Does this reaction cause an increase or decrease in entropy for the system and surroundings?
Increase in Ssurr Increase in Ssys
The dissolution of a molecular solute in a polar solvent (e.g., sugar dissolving in water) typically results in a(n) _____ in entropy because both the molecules in the system and their energies are dispersed in a _____ volume.
Increase, larger
If the reaction shown below is to be coupled to a second reaction in order to generate an overall spontaneous process, what must be true regarding this second reaction? Fe2O3(s) → 2 Fe(s) + 3232 O2(g); ΔG = 740.98 kJ
The free-energy change must be more negative than -740.98 kJ. Reason: A ΔG greater than 740.98 kJ for the second reaction would result in a positive ΔG for the overall process. The overall process would note be spontaneous.
Three molecules are contained in a volume that consists of 4 cells. If the volume is expanded to include a total of 8 cells, how will the number of energetically equivalent states change?
The number of states will triple. Reason: For N molecules in X cells, the number of states is W = XN, so the number of states will increase by 23, or a factor of 8.
Match the prediction of the spontaneity of a given process with the appropriate combination of ΔH and ΔS values. Instructions
The reaction is always spontaneous ifmatchesChoice, ΔH < 0 and ΔS > 0. The reaction is always nonspontaneous ifmatchesChoice, ΔH > 0 and ΔS < 0. The reaction is spontaneous only at low T ifmatchesChoice, ΔH < 0 and ΔS < 0. The reaction is spontaneous only at high T ifmatchesChoice, ΔH > 0 and ΔS > 0.
Which of the following options correctly describe standard entropy? Select all that apply. Multiple select question. The standard entropy of a substance is its absolute entropy at 1 atm. Standard entropy values for elements and compounds are typically negative. The units of standard entropy are JK⋅mol. The standard entropy for any pure element in its standard state is zero. Standard entropy values by definition refer to a system temperature of 25°C.
The standard entropy of a substance is its absolute entropy at 1 atm. The units of standard entropy are JK⋅mol.
The third law of thermodynamics states that a perfect , of a pure solid substance has entropy at a temperature of 0 K.
crystal Blank 2: zero, no, or 0
The sign of which quantity indicates whether or not a particular reaction or process will occur spontaneously?
ΔG Reason: ΔG is the free-energy change for the reaction under the actual conditions of the reaction. This quantity indicates whether or not the process will occur spontaneously under the given set of conditions.
Match the value of the Gibbs free energy change for a reaction with its implication. Instructions ΔG< 0 ——- ΔG> 0 ——- ΔG = 0 ——
ΔG < 0, Spontaneous process ΔG > 0 Nonspontaneous process ΔG = 0 Process at equilibrium
Under equilibrium conditions, the equation ΔG = ΔGo + RT ln Q simplifies to which of the following?
ΔGo = -RT ln K
Match the values of ΔGo with associated equilibrium constants. (Note that all ΔGo values are rounded to 1 significant figure.) Instructions ΔGo = 0 ΔGo = +100 kJ ΔGo = -100 kJ ΔGo = -10 kJ
ΔGo = 0———-K = 1 ΔGo = +100 kJ———K = 3 x 10^-18 ΔGo = -100 kJ——-K = 3 x 10^17 ΔGo = -10 kJ———K = 5 x 10^1
A reaction is found to be spontaneous only at high temperatures. Which of the following must be true? Select all that apply.
ΔHorxn > 0 ΔSorxn > 0
Which of the following options correctly show how to calculate the entropy change of a system? Select all that apply
ΔS = Sfinal - Sinitial ΔS = k ln Wfinal/Winitial ΔS = nR ln Vfinal/Vinitial
At a certain temperature, the change in entropy of the system is calculated to be ΔSsys. If the system is at equilibrium, what is the value of ΔSsurr under these conditions?
ΔSsurr = -ΔSsys
A particular process results in a decrease in the entropy of the system. If this process is spontaneous, what must be true about the entropy change of the surroundings?
ΔSsurr > -ΔSsys
Which of the conditions described below will result in a spontaneous reaction? Select all that apply. Multiple select question. ΔSsys = -20 J/K; ΔSsurr = 25 J/K ΔSsys = 5 J/K; ΔSsurr = -7 J/K ΔSsys = 30 J/K; ΔSsurr = 10 J/K ΔSsys = -9 J/K; ΔSsurr = -2 J/K
ΔSsys = -20 J/K; ΔSsurr = 25 J/K ΔSsys = 30 J/K; ΔSsurr = 10 J/K
