Chemistry Final Exam
What is the equilibrium constant K for the following reaction at 298 K? H2 (g) + Br2 (l) = 2 HBr (g) ΔGo = -106.4 kJ/mol
4.48 x 10^18 ΔGo = -RT ln Keq Keq = e^(-Delta G^o/RT)
± Cell Potential and Free Energy
Free-energy change, ΔG∘, is related to cell potential, E∘, by the equationΔG∘=−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.
Here is the concentration of butyl chloride (C4H9Cl) as a function of time. How does the instantaneous rate of reaction change as the reaction proceeds? Why?
It decreases because the concentration of C4H9Cl decreases.
Use the table of standard reduction potentials given above to calculate the equilibrium constant at standard temperature (25 ∘C) for the following reaction: Fe(s)+Ni2+(aq)→Fe2+(aq)+Ni(s) Ni= .26 Fe= -.44
K = 2.68×10^6 When E∘>0 and K>1 the reaction favors the products. 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. e^14.8 = 2678500
Which will form neutral solution when dissolved in water? K2CO3, Cu(NO)3, NH4Cl, KCl
KCl (Strong base and strong acid) K2CO3 (K2 is strong base) Cu(NO)3 (NO3 is weak acid) NH4Cl (Weak base and strong acid)
Adding which of these substances to the following equilibrium will cause the pH to increase? HF(aq)+H2O(l)⇌F- (aq)+H3O+ (aq) A) NaCl (aq) B) HF (aq) C) KF D) H2O (l)
KF
What is the acid/ base and conjugate base/acid: A) NH3 (aq) + H2O (l)= NH4^+ (aq) + OH^- (aq) B) HCl (aq) + H2O (l)= H3O^+ (aq) + Cl^- (aq)
NH3= Base H2O= Acid NH4^+= Conjugate acid OH^-= Conjugate base HCl= Acid H2O= Base H3O^+ = Conjugate acid Cl^- = Conjugate base
Which is a stronger base? NO3^- or NO2^-? HCO3^- or CO3^2-?
NO2^- More oxygens = more acidic Also, HNO3 is a strong acid, so we know that NO3^- is a weak base CO3^2- Fewer hydrogens= more basic
What is the oxidation and reduction half reaction for: Zn (s) + Cu2+ (aq) = Zn2+ (aq) + Cu (s)
Oxidation 1⁄2 -reaction (Anode): Zn (s) = Zn2+ (aq) + 2 e- Reduction 1⁄2 -reaction (Cathode): 2 e- + Cu2+ (aq) = Cu (s)
A Br∅nsted-Lowry acid is defined as a substance that ________.
acts as a proton donor
7 Strong Acids
hydrochloric acid (HCl) nitric acid (HNO3) sulfuric acid (H2 SO4) hydrobromic acid (HBr) hydroiodic acid (HI) perchloric acid (HClO4) chloric acid (HClO3)
Integrated Rate Law for 1st order reaction
ln[A]t= -kt+ ln[A]0
Units of Concentration
mass %=mass of component/total mass of solution×100% mole fraction (X)=moles of component/total moles of solution molarity (M)=moles of solute/liters of solution molality (m)=moles of solute/mass of solvent (kg)
Formula for half-life equation for first-order reactions:
t(1/2)=0.693/k where t1/2 is the half-life in seconds (s), and k is the rate constant in inverse seconds (s^−1).
Equilibrium
the rates of the forward and reverse reactions are equal
Gibb's free energy of a reaction
ΔG = ΔGo + RT ln Q R= 8.314 J/mol-K ΔG^o = Gibbs free energy under "standard conditions" (298 K, 1 atm, 1M [soln]) Q = reaction quotient: experimental product & reactant concentration - can be anything ΔG^o is the Gibbs free energy change under "standard conditions" ΔG = ΔG^o + RT ln ([products]/[reactants]) ΔG = ΔG^o + RT ln 1/1 ΔG =ΔG^o "Standard conditions": • 1atm • 1 M concentrations Large values of K (at room temperature): ΔGo < 0 Small values of K (at room temperature): ΔGo > 0
Gibb's Free Energy Change
ΔG = ΔH-TΔS A reaction is spontaneous if ΔG is negative -A measure of the amount of "useful work" a system can perform -Endergonic: If ΔG>0, the reaction in the forward direction is non-spontaneous but the reverse reaction is spontaneous. At equilibrium, Reactions with ∆G° < 0 are product favored *If DeltaG< 0 (exergonic)/Spontaneous *If DeltaD>0 (exergonic)/ non-spontaneous
Chapter 20 Equations
ΔGo = - RT lnK Nernst: Eo = (RT/nF) lnK Spontaneity of redox reactions: ΔGo = - n F Eo n = # electrons transferred F = Faraday's constant
Calculate the standard free-energy change at 25 ∘C for the following reaction: Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s)
ΔG∘ = −3.71×105 J Delta G = -nFEo
A mixture of gases has a total pressure of 17.9 atm. One of the gases has a partial pressure of 5.3 atm. What is the mole fraction of this gas in the mixture?
X= .30 P1=X*PTotal X= Mole fraction= number of moles of component/total number of moles
Consider the following reaction: 2H2 (g) + O2 (g) → 2H2O(l) ∆S = -326.3 J/K, ∆H = -571.7 kJ, and ∆G = -475.3 kJ at 25oC. Does the decomposition of water ever become spontaneous? Why?
Yes, at T= 1755 At high T, reaction will become spontaneous
Nernst Equation
Ecell= E°cell - (RT/nF) (lnQ) At 25 DegC, Eo - (0.0592/n) logQ
N2 (g) + 3F2 (g) ⇌ 2NF3 (aq) ΔH°= -250 kJ, ΔS°= -268 J/K Calculate the value of ΔG° for the following reaction at 25°C.
-170 kJ Reaction is spontaneous at low temperatures only
Le Chatelier's Principle
-If a system at equilibrium is disturbed, it will shift its eq so as to counteract the disturbance. -After equilibrium is re-established, Keq is the same as before -After new eq is established, the concentration of reactants/products is different, but the ratio (key) is the same - Solid and Liquid Solutes: Endothermic (absorbs heat) dissolution processes NH4NO3 (s) + HEAT = NH4+ (aq) + NO3- (aq) DeltaH > 0 => solubility increases with T Exothermic (gives off heat) dissolution process: MgSO4 (s) = Mg2+ (aq) + SO42- (aq) + HEAT DeltaH < 0 => solubility decreases with T *Solubility of gas in water decreases with increasing temperature
The mean molar mass of the atmosphere of Titan, one of Saturn's moons, is 28.6 g/mol. The surface temperature is 95K, and the pressure is 1.6 atm. What is the density of Titan's atmosphere?
5.8699 g/L Density= (Molar mass* Pressure)/(Rate*Temp)
Arrange the compound in series of increasing acid strength: H2SO4, H2SeO3, H2SeO4
H2SeO3 < H2SeO4 < H2SO4 First, look at which has more oxygen: Oxyacids (Y-O-H): Increasing number of Oxygen atoms on Y increase acid strength The, look at electronegativity (If two are in same column, the one higher up has larger electronegativity) -Acid strength increase with increasing electronegativity of Y -In this example, Y is Se and S
Order from strongest to weakest acid: AsH3, HBr, KH, H2Se
HBr, H2Se, AsH3, KH
What is the H+ concentration for an aqueous solution with pOH = 3.24 at 25 ∘C?
[H+] = 1.7×10−11 M
Determination of Ka from Titration Curves
pKa = pH Ka = 10-pKa
Classify each of the following reactions as one of the four possible types: 1. spontaneous at all temperatures; 2. nonspontaneous at all temperatures; 3. spontaneous at low T; nonspontaneous at high T; 4. spontaneous at high T; nonspontaneous at low T. (a) N2(g)+3F2(g)→2NF3(g);ΔH∘=−249kJ;ΔS∘=−278J/K (b) N2(g)+3Cl2(g)→2NCl3(g);ΔH∘=460kJ;ΔS∘=−275J/K (c) N2F4(g)→2NF2(g);ΔH∘=85kJ;ΔS∘=198J/K
(a). Spontaneous at low T; non-spontaneous at high T (b). Non-spontaneous at all temperatures (c). Spontaneous at high T; non-spontaneous at low T.
Le Chatelier's Principle: Pressure/Volume N2 (g) + 3 H2 (g) = 2 NH3 (g) If the volume is decreased, how will the reaction respond to relieve the stress? If the volume is increased, how will the reaction respond to relieve the stress?
-A decrease in volume leads to an increase in pressure (increase in the "concentration" of molecules) The system will respond by shifting to the side that has fewer molecules => rxn will shift to the right (fewer molecules) It will consume reactants to make products. Rightward shift It will consume products to make reactants.
Galvanic Cells
-A galvanic cell (or voltaic cell) produces electricity using a spontaneous redox reaction -The components of this reaction are separated by a salt bridge and connected with a wire, forcing the electrons to travel across the wire, creating electricity. -The salt bridge is a U-shaped glass tube that is filled with a gel-like substance containing a salt. The salt bridge completes the circuit and allows ions to flow, maintaining electrical neutrality in the solutions.
PCl5 (g) ⇌ PCl3 (g)+ Cl2 (g) A) If Keq=0.497, will there be more PCL5 or PCL3 at equilibrium? B) If a 2L flask contains 1.72 moles of PCl5 and .7 moles of PCl3 at eq, what is concentration of Cl2 at equilibrium C) What will be the result of adding PCl3 to the reaction? D) What is K^1eq for the reverse reaction?
-Reactant favored -Equilibrium lies to left because Keq<1 Concentration of Cl2= 1.22 M .497= (x*.350)/(.860) C) It will shift to the left. Keq will not change because equilibrium will be re-established (graph will go straight up, then level off at level higher than initial) D) 1/.497= 2.01
Oxidation-Reduction Reactions (Redox Reactions)
-Reactions that involve the transfer of electrons from one species to another. -In general, one element will lose electrons (oxidation), with the result that it will increase in oxidation number, and another element will gain electrons (reduction), thereby decreasing in oxidation number. An oxidizing agent is an element or compound in a redox reaction that oxidizes another species and itself gets reduced and is therefore the electron acceptor in the reaction. A reducing agent is an element or compound in a redox reaction that reduces another species and itself gets oxidized and is therefore the electron donor in the reaction. -Oxidation means an increase in oxidation state and a loss of electrons and involves a reducing agent. -Reduction means a decrease in oxidation state and a gain of electrons and involves an oxidizing agent.
Solutions A 41.5 g sample of calcium chloride is dissolved in 100 g of water at 45 °C. The solution is cooled to 20.0 °C and no precipitate is observed. This solution is ________. A 81.5 g sample of calcium chloride is dissolved in 102 g of water at 45 °C. The solution is cooled to 20.0 °C and no precipitate is observed. This solution is ________.
-Saturated solution: dissolved solute in equilibrium with undissolved solute -Unsaturated solution: more solute could be dissolved -Supersaturated solution: more solute is dissolved than in a saturated solution (not at equilibrium) A) Unsaturated (Below curve) B) Supersaturated (Inside Curve)
List the following aqueous solutions in order of decreasing freezing point: 0.040 m glycerin (C3H8O3), 0.020 m KBr, 0.030 m phenol (C6H5OH). Rank solutions from highest freezing point to lowest freezing point. To rank items as equivalent, overlap them.
0.030 m phenol (C6H5OH), 0.020m KBr & 0.040 m glycerin (C3H8O3) - Last two are tied
A 50.0 mL sample of a solution of a monoprotic acid is titrated with a 0.115 M NaOH solution. The titration curve below was obtained. The concentration of the monoprotic acid is about: (Value of titration curve at equilibrium = 25 mL)
0.06 mol/L Macid*Volume(acid)= Mbase*Volume(base) (0.0115 X 25 ml) / (50 ml)
Calculate the concentration of CO2 in a soft drink that is bottled with a partial pressure of CO2 of 4.0 atm over the liquid solution at 25oC. The Henry's Law constant, k, for CO2 in water at 25oC is 3.4 x 10-2 mol/(L atm).
0.14 M -Henry's Law= Sg=k*Pg -S= 3.4*10^-2 * 4 atm *Henry's Law states that as pressure increases, solubility increases/ as pressure decreases, solubility decreases
A 1 L reaction vessel is filled with 0.50 moles SO3 (g) at 1000K. At equilibrium the concentration of SO3 is 0.20 M. What is the value of Keq at 1000K? 2SO3 (g)⇌2SO2 (g)+O2 (g)
0.34 Keq= (0.3)^2*.15 / (0.2)^2
What is the concentration of HCHO2 solution that has pH of 1.93. Ka = 1.8*10^-4 HCHO2 (aq) H+ (aq) + CHO2- (aq)
0.80 M I x 0 0 C -.012 .012 .012 E x-.012=x .012 .012 HCHO2=x= (.012)^2/ (1.8*10^-4)
What is the concentration of a formic acid (HCHO2) solution that has a pH of 1.85? (Ka = 2.1 x 10-4) HCHO2 (aq) ⇌ H+ (aq) + CHO2- (aq) What is the pH of a .10 M solution of HCHO2 if Ka=1.8*10^-4
0.93 M 2.37 1.8*10^-4 = x^2/.10 -log[.0042] = 2.37
In 2018, Hurricane Florence made landfall in Wilmington. At the time of landfall, the pressure had dropped to 27.9 in Hg. What was the pressure in atm? (1 inch = 25.4 mm)
0.932 atm 27.9 in Hg * (25.4 mm/1 in Hg) 708.66 mmHg (1 atm/760 mmHg)
How does the entropy (ΔS) of the system change in the following processes? (1) The melting of ice cubes at 10∘C and 1 atm pressure (2) Separating a mixture of N2 and O2 into two separate samples, one that is pure N2 and one that is pure O2 (3) The reaction of sodium metal with chlorine gas to form sodium chloride (4) The dissolution of CH3OH (l) in water to form CH3OH (aq) (5) alignment of iron filings in a magnetic field;
1 and 4 Increase 2, 3 and 5 Decrease
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. (2 electrons lost from 2I- to I2)
For the reaction A+B+C→D+E, the initial reaction rate was measured for various initial concentrations of reactants. The following data were collected: Trial [A](M) [B](M) [C](M) Initial rate(M/s) 1 0.50 0.50 0.50 1.5×10−4 2 0.50 0.50 1.50 4.5×10−4 3 1.00 0.50 0.50 6.0×10−4 4 1.00 1.00 0.50 6.0×10−4 1. What is the reaction order with respect to A? 2. What is the value of the rate constant k for this reaction? 3. Given the data calculated in Parts A, B, C, and D, determine the initial rate for a reaction that starts with 0.85 M of reagent A and 0.80 M of reagents B and C?
1. 2 2. k = 1.2×10−3 M^−2⋅s^−1 (4.510^-4=k[.5]^2[1.5] 3. 6.9×10−4 M/s
Calculate Oxidation values for: 1. FeO3 2. O3 3. MgCl 4. LiOH 5. H2O2 6. NH4+ 7. HSO4- 8. ClO2- 9. Cr2O7^2- 10. K2O2
1. Fe (+6), O (3*-2) 2. O (3*0=0) 3. Mg (+2), Cl (-2) 4. Li (+1), O (-2), H (+1) - Start with Li value 5. H2 (2*1), O (2*-1) 6. N (-3), H (4*1) = 1 7. H (1), S (6), O (4*-2)= -1 8. Cl (3), O (2*-2)= -1 9. Cr (2*6), O (7*-2) = -2 10. K (2*1), O (2*1) - Start with K (rule 4)
Predict the sign of the entropy change, ΔS∘, for each of the following reactions. 1. Ag+(aq)+Cl−(aq)→AgCl(s) 2. CaCO3(s)→CaO(s)+CO2(g) 3. 2NO2(g)→N2(g)+2O2(g) 4. 2Mg(s)+O2(g)→2MgO(s) 5. C4H8(g)+6O2(g)→4CO2(g)+4H2O(g) 6. H2O(l)→H2O(g)
1. Negative (Reactants are more random/disordered, thus, entropy decreases in the change from reactants to products.) 2. Positive (Products are more random/disordered, thus, entropy increases in the change from reactants to products.) 3. Positive (Products are more random/disordered, thus, entropy increases in the change from reactants to products.) 4. Negative (Reactants are more random/disordered) 5. Positive (Products are more random/disordered, thus, entropy increases in the change from reactants to products.) 6. Positive (Products are more random/disordered, thus, entropy increases in the change from reactants to products.)
A cylinder with a movable piston contains 2.00 g of helium, He, at room temperature. More helium was added to the cylinder and the volume was adjusted so that the gas pressure remained the same. How many grams of helium were added to the cylinder if the volume was changed from 2.00 L to 3.10 L ? (The temperature was held constant.)
1.10 grams -V1/n1=V2/n2 -3.1g-2g=1.10 grams
A certain first-order reaction has a rate constant of 1.10×10−3 s−1. How long will it take for the reactant concentration to drop to 1/8 of its initial value? (Half life equation)
1.89×103 s -(630 seconds * 3)
Calculate the boiling point of a solution prepared by dissolving 45 g of NaCl in 200 g of water? (Kb = 0.512 oC /m).
104 deg C DeltaTb= I*kb*m I= 2 m= mol/kg
Calculate the boiling point of a solution prepared by dissolving 45.0 g of NaCl in 100. g of water? (Kb = 0.512 oC/m, i(NaCl)= 2)
108 DegC
The atmosphere is a mixture of gases with a total pressure equal to the barometric pressure. A sample of the atmosphere at a total pressure of 750 mm Hg is analyzed to give the following partial pressures: P(N2) = 575 mmHg, P(Ar) = 7.9 mm Hg, P(CO2) = 0.2 mm Hg, P(H2) = 3.0 mm Hg What is the partial pressure of O2(g) in this sample of the atmosphere?
164 mmHg PTotal=586.1 mmHg P1=X*PTotal
NH4+ has a Ka of 5.5 x 10-10. Calculate the pOH of a 2.0 M solution of NH3. NH3 (aq) + H2O (l) ⇌ NH4+ (aq) + OH- (aq)
2.2
What is the emf for a galvanic cell that employs the following balanced overall cell reaction: 2 Al (s) + 3 I2 (s) = 2 Al3+ (aq) + 6 I- (aq) I2 (s) + 2e^- = 2I (aq) = 0.54 Al3+ (aq) + 3e^- = Al (s) = -1.66 What is the emf for a cell employing the reaction below if [Al3+] = 0.004M and [I- ] = 0.010M at 298K? 2Al(s) + 3I2 (s) → 2Al3+ (aq) + 6I- (aq)
2.2 V Eordn are independent of stoichiometric factors ! V = J/C (energy per charge transferred) = const. 2.37V Q= [I- ]6 [Al3+]2= 0.0106 × 0.0042 = 1.6 × 10^-17 Eo = (RT/nF) lnK n=6 E = 2.20 V- .0592/6 * log(1.6 × 10^-17)
The Ag+ concentration in a saturated solution of AgCl is 1.5 x 10-5 M. What is the solubility product (Ksp) of AgCl ? AgCl (s) ⇌ Ag+ (aq) + Cl- (aq) The Ag+ concentration in a saturated solution of AgCl is 1.3 x 10-5 M. What is the solubility product of AgCl ?
2.3*10^-10 1.7*10^-10 AgCl (s) = Ag+ (aq) + Cl- (aq) Ksp = [Ag+][Cl-] = (1.3 x 10-5)2 = 1.7 x 10-10
As a scuba diver descends under water, the pressure increases. At a total air pressure of 2.82 atm and a temperature of 25.0 ∘C, what is the solubility of N2 in a diver's blood? [Use the value of the Henry's law constant k calculated in Part A, 6.26×10−4mol/(L⋅atm).] Assume that the composition of the air in the tank is the same as on land and that all of the dissolved nitrogen remains in the blood. Express your answer with the appropriate units. -Henry's Law
2.82*.78=2.1996 2.1996*6.2610^-4 = .0013772 solubility = 1.38×10−3 molL *greatest molar solubility in water= largest Ksp value
When heated, calcium carbonate decomposes to yield calcium oxide and carbon dioxide gas via the reaction CaCO3(s)→CaO(s)+CO2(g) What is the mass of calcium carbonate needed to produce 47.0 L of carbon dioxide at STP?
210 g -2.1 mol CaCO3 * 100g/mol = 210 g
Balancing Redox Equations in Basic Solution: Cu(s) + 4 H+ (aq) + 2 NO3- (aq) → Cu2+ (aq) + 2 NO2 (aq) + 2 H2O (l)
2H2O (l) + Cu + 2NO3^- = Cu^2+ + 2NO2 + 4OH^- In a basic solution, H+ need to be replaced by OH- in the final equation! Take H2O on right, move to left Take 4H+ on left, add 4OH- on right
The iodate anion (IO3^-) reacts with SO3^- to form iodide (I-) and X according to the reaction IO3^- +3SO3^- = 1^- + X The IO3- ions disappear at rate of 8*10^-5 Ms^-1. The unknown compound appears at rate of 2.4*10^-4 Ms^-1. What is the coefficient?
3 rate[A] = -delta[A]/delta t -delta[IO3-]/delta t = 1* Delta [x]/?delta t 8*10^-5 = 1/? * 2.4 * 10^-4
What is the equilibrium constant K for the following reaction at 298 K? H2 (g) + Br2 (l) ⇌ 2HBr (g) ΔG°= -100.0 kJ/mol R= 8.314 J mol-1 K-1
3.38 x 10^17 e^-(-100000/8.314*298)
How long does it take a person at rest to breathe one mole of air if the person breathes 81.0 mL/s of air that is measured at 25 ∘C and 755 mmHg? Express your answer numerically in seconds.
304 Seconds -In one second, person breathes .0033 moles
How many milliliters of 0.220 M HCl are needed to titrate each of the following solutions to the equivalence point? (1) 90.0 mL of 9.50×10−2 M NaOH (2) 20.0 mL of 0.118 M NH3
38.9 mL 10.7 mL
Consider the following elementary steps that make up the mechanism of a certain reaction: 3A→B+C B+2D→C+F What is the intermediate? What is the rate law for step 1? What is the rate law for step 2?
3A+2D→2C+F (3A+B+2D→B+C+C+F) The intermediate is B (Doesn't appear at the beginning or end) Rate law for step 1: Rate = k[A]^3 Rate law for step 2: Rate = k[B][D]^2
What is the pH of a buffer mixture made of 0.20 M acetic acid (CH3CO2H or HOAc) and 0.1 M sodium acetate (NaCH3CO2 or NaOAc)? Kb for acetate = 6.0 x 10-10 HOAc (aq) + H2O (l) ⇌ OAc- (aq) + H3O (aq)
4.5 pH= pKa + log(base/acid)
What is H^+ in .01 M Ca(OH)2 solution? Ca(OH)2= Ca^2+ + 2OH^- B) Calculate pH for strong base solution: 13.0 mL of 1.60×10−2 M Ca(OH)2 diluted to 490.0 mL . pH = 10.929
5.0*10^-13 -log[.01*2] = 1.69 pOH 14-1.69 = 12.3 pH 10^-12.3 = 5*10^-13 *Same applies for MgOH2 B) t's OH2, so multiply 4.245*10^-4 X 2
Butane, C4H10, is a component of natural gas that is used as fuel for cigarette lighters. The balanced equation of the complete combustion of butane is 2C4H10(g)+13O2(g)→8CO2(g)+10H2O(l) At 1.00 atm and 23 ∘C, what is the volume of carbon dioxide formed by the combustion of 3.40 g of butane?
5.69L 1.4L C4H10*(8/2)=5.69L CO2
2N2O5(g) = 4NO2(g) + O2(g) Time, (s). [N2O5] (M) 0 0.200 10 0.0905 20 0.0820 30 0.0741 40 0.0671 50 0.0549 19. What is the average rate of appearance of NO2 from t=0 s to t=50 s? A) 1.4x10-3 M/s B) 2.9x10-3 M/s C) 5.8x10-3 M/s D) 0.200 M/s
5.8x10-3 M/s
Helium-oxygen mixtures are used by divers to avoid the bends and are used in medicine to treat some respiratory ailments. What percent (by moles) of He is present in a helium-oxygen mixture having a density of 0.498 g/L at 25 ∘C and 721 mmHg?
68.5% He If D=mass/V and molar mass=mass/moles, then molar mass= rTD/P Molar Mass= (.08206298K.498)/.949= 12.8 g/mol 12.8= x/100 (4 g/mol)+ (100-x)/100 (32 g/mol)
A 0.18 M solution of hydrofluoric acid (HF) is found to have a pH of 1.96. What is the value of Ka? HF (aq) ⇌ H+ (aq) + F- (aq)
7.16 x 10-4 HF H+ F- .18 0 0 -.011 +.011 +.011 .169 .011 .011 Ka = [.011][.011]/[.169] = 7.2*10^-4 -Ka is less than one, so it goes to left to reach equilibrium (Towards reactants)
Air bag has volume of 36L and is to be completely filled with nitrogen gas at 1.15 atm and 26 DegC, how many grams of NaN3 must be decomposed? 2NaN3 (s) + heat = 2Na (s) + 3N2 (g)
73 grams NaN3 PV=nRT 1.15*36L=n(0.08206)(299.15k) n=1.686 moles of n2 1.686* (2/3)*(65.02 g/mol)
Determine the pH of a 0.60 M solution of KF. The Ka for hydrofluoric acid is 7.1 x 10-4.
8.5 -log(2.907*10^-6)
The rate constant for a certain reaction is k = 3.70×10−3 s−1 . If the initial reactant concentration was 0.750 M, what will the concentration be after 20.0 minutes? 2. A zero-order reaction has a constant rate of 4.90×10−4 M/s. If after 80.0 seconds the concentration has dropped to 2.00×10−2 M, what was the initial concentration?
8.85×10−3 M First step is to determine the order: Observe that the units of the rate constant for this reaction are s−1. The units of the rate constant can be used to determine the overall order of the reaction based on the rate law. Consider the following rate law. rate=k[A]x M/s=s^−1×M^x What does x have to be for the units to come out correctly? (1) Next, use equation A= A0e^(-kt) = 0.750e^(-4.44) 2. 5.92×10−2 M (k=4.90×10−4 M/s) 4.910^-4 M/s 80= 0.0392+0.02
Calculate the equilibrium constant K at 25°C for the following reaction NH3 (g) + HCl (g) ⇌ NH4Cl (s) ∆H° = -176 kJ; ∆S°= -285 J/K
9.20 × 10^15 ΔG= ΔH-TΔS lnKeq = -DeltaG/RT Keq= e^(-DeltaG/RT)
Catalyst
A catalyst decreases the activation energy of a reaction. *Note: A catalyst does not affect the enthalpy change of a reaction -Something at the beginning and at the end -Speeds up the reaction without being consumed in the process -Works by lowering the overall Ea for the reaction/Decreases activation energy -Both forward and backward rate constants are increased -Keq stays the same -Rate at which equilibrium is reached is increased -Does not effect enthalpy change -May provide new reaction pathway -Brings reactants physically closer together -Weakening existing chemical bonds -Twisting reactants into position from which reaction is more likely *Shortest Ea = fastest reaction
A negative enthalpy value indicates an:
A negative enthalpy value indicates an exothermic reaction.
A) Describe the electrodes in this zinc-copper galvanic cell: Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s) (Zinc on the left, copper on right) B) What is the standard potential, E∘cell, for this galvanic cell?
A) Zinc: Anode/Loses mass/Oxidized Copper: Cathode/Gains mass/Reduced (gains electrons) B) E∘cell = 1.100 V
A) What is the oxidation state of an individual sulfur atom in MgSO4? B) What is the oxidation state of an individual nitrogen atom in NH2OH? C) What is the oxidation state of an individual phosphorus atom in PO33−? D) What is the oxidation state of each individual carbon atom in C2O42−?
A) +6 B) -1 C) +3 D) +3
A mixture of 0.10 mol of NO, 0.050 mol of H2, and 0.10 mol of H2O is placed in a 1.0-L vessel at 300 K. The following equilibrium is established: 2NO(g)+2H2(g)←−→N2(g)+2H2O(g) At equilibrium [NO]=0.062M. A) Calculate the equilibrium concentration of H2. B) Calculate the equilibrium concentration of N2. C) Calculate the equilibrium concentration of H2O D) Calculate Kc.
A) 1.2×10−2 M B) 1.9×10−2 M C) 0.138 M D) Kc=650
A mixture initially contains A, B, and C in the following concentrations: [A] = 0.300 M, [B] = 1.05 M, and [C] = 0.450 M. The following reaction occurs and equilibrium is established: A (g) + 2B (g) ⇌ C (g) At equilibrium, [A] = 0.100 M and [C] = 0.650 M. A) Calculate the value of the equilibrium constant, Kc B) If the value of the reaction quotient (Qc) is 387, is the reaction at equilibrium? If not, in which direction will it proceed to reach equilibrium?
A) 15.38 B) No, the reaction will proceed in reverse to form reactants.
Determine the oxidation number for the indicated element in each of the following substances: A) S in SO2 B) C in COCl2 C) Mn in MnO−4 D) Br in HBrO E) As in As4 F) O in K2O2
A) 4 B) 4 C) 7 D) 1 E) 0 F) -1 (Rule 4 takes precedence over rule 5)
Is the solution acidic, basic or neutral? A) NH4Br B) Ca(NO2)2 C) Ca(HCO3)2 D) CaBr E) NH4NO2 F) KCl G) LiBr H) NaOCl I) CaSO3 J) NH4Cl
A) Acidic (we know Br is an acid, and we know NH4 is weak base) B) Basic (We know Ca is strong base because its a metal on the far left, and we know the NO2 is not a strong acid, making it weak) C) Basic (Strong base with weak acid) D) Neutral E) Neutral (Weak base and weak acid) F) Neutral (Strong acid and base) G) Neutral (Strong acid and base) H) Basic (Na=strong base, OCl=weak acid) I) Basic J) Acid )NH4=weak base, Cl=strong acid) *STRONGER ACID = WEAKER CONJUGATE BASE *MORE HYDROGENS = MORE ACIDIC
For each of the following pairs, choose the substance with the higher entropy per mole at a given temperature: A) Ar(l) or Ar(g) B) He(g) at 3 atm pressure or He(g) at 1.5 atm pressure C) 1 mol of Ne(g) in 15.0 L or 1 mol of Ne(g) in 1.50 L D) CO2(g) or CO2(s)
A) Ar (g) B) He(g) at 1.5 atm pressure C) 1 mol of Ne(g) in 15.0 L D) CO2(g)
FeO+CO→Fe+CO2 A) Which element is oxidized in this reaction? B) Which substance is the oxidizing agent in this reaction? Cr2O72−+3HNO2+5H+→2Cr3++3NO3−+4H2O C) Which element is reduced in this reaction? D) Which substance is the reducing agent in this reaction?
A) Carbon is oxidized B) FeO is the oxidizing agent C) Cr is reduced D) HNO2 is the reducing agent.
Calculate the standard emf for each of the following reactions: A) Cl2(g)+2I−(aq)→2Cl−(aq)+I2(s). B) Ni(s)+2Ce4+(aq)→Ni2+(aq)+2Ce3+(aq).
A) E∘ = 0.823 V B) E∘ = 1.89 V
Calculate the standard emf for each of the following reactions: A) Fe(s)+2Fe3+(aq)→3Fe2+(aq). B) 2NO−3(aq)+8H+(aq)+3Cu(s)→2NO(g)+4H2O(l)+3Cu2+(aq).
A) E∘ = 1.211 V B) E∘ = 0.62 V
A voltaic cell utilizes the following reaction and operates at 298 K: 3Ce4+(aq)+Cr(s)→3Ce3+(aq)+Cr3+(aq). A) What is the emf of this cell under standard conditions? B) What is the emf of this cell when [Ce4+]= 1.9 M , [Ce3+]= 0.13 M , and [Cr3+]= 1.6×10−2 M ? C) What is the emf of the cell when [Ce4+]= 7.0×10−3 M ,[Ce3+]= 2.0 M , and [Cr3+]= 1.9 M ?
A) E∘ = 2.35 V B) E = 2.5 V C) E = 2.2 V
Overall cell reaction: Fe(s)+2Ag+(aq)→Fe2+(aq)+2Ag(s) A) What is being oxidized? B) What is being reduced? C) Write the half-reactions that occur in the two electrode compartments. Which is anode/cathode? D) Indicate the signs of the electrodes. E) Do electrons flow from the silver electrode to the iron electrode, or from the iron to the silver? F) In which directions do the cations and anions migrate through the solution?
A) Fe B) Ag+ C) anode reaction: Fe(s)→Fe2+(aq)+2e− cathode reaction: Ag+(aq)+e−→Ag(s D) Fe electrode is negative, Ag electrode is positive. E) Electrons flow from the iron electrode to the silver electrode. F) Cations migrate to the silver electrode, anions migrate to the iron electrode.
Rank the following compounds in order of decreasing acid strength using periodic trends: HCl, HBr, BH3, H2S H2SO3, H2SO4, H2S What is the strongest acid? C) H2SO4, H3NO3, H2NO3 D) HBrO2, HIO2, HBrO3, HIO3
A) HBr, HCl, H2S, BH3 Acid strength increases as you move down a group. Acid strength increases from left to right across a period. More oxygens/ higher electronegativity= more acidic B) H2SO4, H2SO3, H2S C) H2SO4 (More Oxygens often means more acidity) D) HBrO3
What are the criteria for spontaneity: A) in terms of entropy? B) in terms of free energy?
A) In any spontaneous process the entropy of the universe increases. B) In any spontaneous process operating at constant temperature, the free energy of the system decreases.
Choose the stronger reducing agent: A) Fe(s) or Mg(s). B) Ca(s) or Al(s). C) H2 (g, acidic solution) or H2S(g) D) BrO−3(aq) or IO−3(aq).
A) Mg (s) B) Ca (s) C) H2 (g, acidic solution) D) IO−3(aq)
Among the following reactions, identify which ones are redox reactions (and the oxidizing agent if they are redox reactions) A) NO2- (aq) + H+ (aq) = HNO2 (aq) B) 4Al(s) + 3O2 (g) = 2Al2O3 (s) C) 3Cl2 (g) + 2Fe(s) 2FeCl3 (s)
A) No redox B) Oxidizing agent = O2 C) Oxidizing agent = Cl2
How will the following equilibria respond to an increased pressure caused by decrease in volume? A)3NO = N2O + NO2 B)N2+O2 = 2NO C) 2Cl2 + 2H2O = 4Cl + O2
A) Reaction will shift to the right (Towards products) -A decrease in volume = increase pressure, increase in concentration of molecules -System will respond by shifting to side with fewer molecules (To the right because 4>2) B) No influence (2=2) C) Reaction will shift left (towards reactants) *Adding to products shifts reaction to left *What would happen to these equilibria if the pressure was increased by the addition of an inert gas? nothing b/c "concentrations" don't change
Calculate the pH of each of the following strong acid solutions. A. 2.69×10−2 M HNO3 B. 0.590 g of HClO3 in 2.30 L of solution. C. 10.00 mL of 2.00 M HCl diluted to 0.530 L . D. A mixture formed by adding 59.0 mL of 2.5×10−2 M HCl to 120 mL of 1.5×10−2 M HI.
A. pH = 1.570 B. pH = 2.518 C. pH= 1.423 D. pH= 1.74 M1V1=M2V2
Predict whether the following solutions are acidic or basic: 0.10 M NH4Br 0.15 M Fe(NO3)3 0.15 M Ca(NO2)2
Acidic Acidic Basic
Definition of Acids and Bases
Arrhenius Definition (1887) Acids must dissolve, generate H+ Bases must dissolve, generate OH- • Brønsted-Lowry Definition (1923) Acids: donate H+ (Donates proton), generate H+ Bases: H+ acceptor (Accept proton) HSO3−(aq)+H2O(l)→H2SO3(aq)+OH−(aq) HSO3^- is Bronsted Lowry Base H2O is Bronsted Lowry Acid • Lewis Definition (1923) Lewis acids e- pair acceptors Lewis base e- pair donor
K=2.1×10−20. What can be said about this reaction? Where does the equilibrium of this reaction lie?
At equilibrium the concentration of reactants is much greater than that of products Equilibrium of reaction lies to the left Value of K Reaction favors Reaction lies to K<<<1 reactants left K ~ 1 neither reactants nor products center K>>>1 products right
Determine the pH of 1.00 L of buffer solution, which initially is 0.15 M acetic acid and 0.25 M sodium acetate, before and after adding 0.05 moles of HCl. The Ka for acetic acid is 1.8 x 10-5.
Before: 4.97 After: 4.74 pH= pKa + log([Base]/[Acid])
Which statement about Standard Molar Entropies is false? A) The standard molar entropies of gases are greater than those of liquids and solids, consistent with our interpretation of experimental observations. B) Unlike enthalpies of formation, standard molar entropies of elements at the reference temperature of 298 K are not zero. C) Standard molar entropies generally increase with decreasing molar mass. D) Standard molar entropies generally decrease with a decreasing number of atoms in the formula of a substance.
C) Standard molar entropies generally increase with decreasing molar mass. (False)
Which statement about atmospheric pressure is false? A) As air becomes thinner, its density decreases. B) Air actually has weight. C) With an increase in altitude, atmospheric pressure increases as well. D) The warmer the air, the lower the atmospheric pressure.
C. With an increase in altitude, atmospheric pressure increases as well. (False)
What is the conjugate base of A) HCO3− B) H3PO4 C) HS^- What is the conjugate acid of HPO32− ?
CO3^2− H2PO4^- S^2- H2PO3−
Ascorbic acid (vitamin C, C6H8O6) is a water-soluble vitamin. A solution containing 82.5 g of ascorbic acid dissolved in 230 g of water has a density of 1.22 g/mL at 55 ∘C. Calculate mass percent, mole fraction, molality, and molarity
Calculate the mass percentage of ascorbic acid in this solution. 26.4 % Calculate the mole fraction of ascorbic acid in this solution. 3.54×10−2 Calculate the molality of ascorbic acid in this solution. 2.04 mol/kg Calculate the molarity of ascorbic acid in this solution. M = 1.83 M -(.46875/.256)
Henderson-Hasselbalch Equation
Calculates pH of a buffer pH=pKa+log[A−]/[HA] Another way to express acid strength is by using pKa=−logKa Another way to express base strength is by using pKb=−logKb
Enthalpy
Change in Enthalpy = DeltaH The heat evolved or absorbed in the reaction
Which of the following statements is not true? A) The temperature of a gas sample is related to the average kinetic energy. B) Theaveragespeedofgasmoleculesincreaseswithincreasingtemperature. C) Theaveragekineticenergyofgasmoleculesdecreaseswithdecreasingtemperature. D) The average speed of gas molecules is independent of temperature.
D) The average speed of gas molecules is independent of temperature.
Of the following, which is the strongest acid? A) HClO B) HClO3 C) HClO2 D) HClO4
D) HClO4
Consider the formation of nitryl fluoride: 2NO2 (g) + F2 (g) = 2NO2F (g) The reaction is first order in F2 and second order overall. What is the rate law?
D) Rate=k[NO2][F2]
Which reaction produces a decrease in the entropy (ΔS) of the system? A) CaCO3 (s) ⇌ CaO (s) + CO2 (g) B)2C(s)+O2 (g)⇌2CO(g) C) CO2 (s) ⇌ CO2 (g) D)2H2 (g)+O2 (g)⇌2H2O(l)
D)2H2 (g)+O2 (g)⇌2H2O(l) *B is not correct because 2C(s) is solid, so don't count it
Which one of the following is a valid statement of Avogadro's law? A) = constant B) = constant C) PV = constant D) V = constant × n
D. V= Constant * n
Dissolving a gas in a liquid ___________ the entropy
Decreases (Gas molecules are confined/more organized)
Spontaneity of Redox Reactions
DeltaGo=-nFEo n = # electrons transferred F = Faraday's constant
Two different gases occupy two separate bulbs. Consider the process that occurs when the stopcock separating the gases is opened, assuming the gases behave ideally and do not react.
DeltaH = 0 DeltaS > 0
Activation Energy
Difference in energy between the reactants and the activated complex. Activation energy is always a positive number. (Top hump-reactants) -Minimum energy required to initiate a chemical reaction
Exothermic reaction: Effect of Increasing Temp and decreasing temp Endothermic reaction: Effect of Increasing Temp and decreasing temp
Exo: Increasing T shifts reaction left /It will consume products to make reactants.(Leftward shift)(More reactants, fewer products, lower Keq), decreasing shifts right (More products, fewer reactants, higher Keq) Endo: Increasing T shifts reaction right (More products, fewer reactants, higher Keq), decreasing shifts reaction left (More reactants, fewer products, lower Keq)
Exothermic vs. Endothermic
Exothermic processes release energy, whereas endothermic processes require energy. Endothermic: separation of solvent molecules/separation of solute molecules Exothermic: formation of solute-solvent interactions
Calculate the standard cell potential (E∘) for the reaction X(s)+Y+(aq)→X+(aq)+Y(s) if K = 5.75×10−3.
E∘ = -0.132 V When E∘<0 and K<1 the reaction favors reactants. lnK=nFE∘/RT
Calculate the standard cell potential at 25 ∘C for the reaction X(s)+2Y+(aq)→X2+(aq)+2Y(s) where ΔH∘ = -715 kJ and ΔS∘ = -187 J/K .
E∘ = 3.42 V ΔG∘=−nFE∘ ΔG∘ = -715(1000)- 298(-187) = −6.59×105 J n= 2 mol
Tarnish on iron is the compound FeO. A tarnished iron plate is placed in an aluminum pan of boiling water. When enough salt is added so that the solution conducts electricity, the tarnish disappears. Imagine that the two halves of this redox reaction were separated and connected with a wire and a salt bridge. Calculate the standard cell potential given the following standard reduction potentials: Al3++3e−→Al;E∘=−1.66 V Fe2++2e−→Fe;E∘=−0.440 V
E∘cell = 1.22 V
Among the following pairs, which metal ion will decrease the pH of an aqueous solution more? Fe2+ Fe3+ Zn2+ Cd2+
Fe3+ Zn2+
Electrochemistry
Flow goes from anode to cathode Anode=oxidation (Anode half cell = oxidation occurs) Cathode=Reduction (Cathode half cell= reduction occurs) Cations go from anode to cathode Anions go from cathode to anode The "salt bridge" is a reservoir for cations/anions to replenish electrons and close the electrical circuit Electrons/electricity always headed towards CATHODE Eocell (Cell potential) = Eordn (cathode) - Eordn (anode) *Half-reactions are always written as reductions Substances with more NEGATIVE reduction potentials reduce substances with more positive reduction potentials Substances with very NEGATIVE reduction potentials are good reducing agents (More negative= more likely to be a reduction) Substances with very POSITIVE reduction potentials are good oxidizing agents
The second law of thermodynamics states that: The third law of thermodynamics states that:
For any spontaneous process, the entropy of the universe increases -In a larger container, gases have a larger entropy (more space to spread out = more disorganization- The number of ways to arrange molecules increases with container size) -Larger molecules/atoms generally have a larger entropy than smaller ones -Dissolving a solid or liquid will increase the entropy -An increase in gaseous molecules leads to an increase in entropy -Increase in entropy when gases form from liquids or solids, or when liquids or aqueous solutions form from solids -Lowest temp=higher order= lowest entropy -Higher temp= lower order= higher entropy -No system can reach absolute zero (K=0) -At absolute zero, there would be no molecule movement (Only one micro states)
Consider three gases all at 298 K: HCl, H2, and O2. List the gases in order of increasing average speed.
HCl, O2, H2 On a graph showing molecular speed, the first/tallest curve is the slowest and heaviest, and the most stretched out curve is the lightest and fastest
Which of the following has the largest entropy? A) HI (g) B) HBr (g) C) HCl (g) D) HCl (s)
HI
Compounds composed of a salt and water combined in definite proportions are known as __
Hydrates
In the process of forming a solution, which process is always exothermic? I. Breaking solute-solute interactions II. Forming solute-solvent interactions III. Breaking solvent-solvent interactions
II Only
Consider the reaction: 2N2O5(g) = 4NO2(g) + O2(g) Which curve corresponds to how the concentration of O2 changes over time?
Increasing curve (Products will both be increasing), O2 will be shorter than NO2
If the reaction is at equilibrium and the temperature is lowered, which statement is true? 2NOCl(g)⇌2NO(g)+Cl2 (g)+Heat ΔH<0 A) The reaction will shift to the right to reestablish equilibrium with the same value of K as before the temperature was lowered. B) The reactant concentrations will increase while product concentrations decrease. C) K will increase and the system will shift to the right to reestablish equilibrium. D) There will be no shift in equilibrium since the reaction is exothermic and the system is being cooled.
K will increase and the system will shift to the right to reestablish equilibrium.
Ka and Kb
Ka= [H+][A-]/[HA (Weak Acid)] Kb= [OH-][SA](Strong acid)/[B-](weak base) *Strong acids and bases don't have Ka/Kb value -Strongest base=Smallest Ka value -Acidity increase going down a column -Electronegativity increase going up and right -Acid strength is measured by the acid dissociation constant Ka -The Smaller Ka, the weaker the acid -Larger Ka = lower pH= higher acidity - [H^+] = Sqr root of (ka*HA) -[OH^-]= Sqr root of (Kb*A^-/base) Acidity of each molecule increases as electronegative increases
A mixture initially contains A, B, and C in the following concentrations: [A] = 0.450 M , [B] = 1.25 M , and [C] = 0.300 M . The following reaction occurs and equilibrium is established: A+2B⇌C At equilibrium, [A] = 0.260 M and [C] = 0.490 M . Calculate the value of the equilibrium constant, Kc
Kc=2.49 [.49]/(.26)(.87)^2
The two half-reactions that occur in the cell are Cu2+(aq)+2e−→Cu(s) and Fe(s)→Fe2+(aq)+2e− The net reaction is Cu2+(aq)+Fe(s)→Cu(s)+Fe2+(aq) Calculate Keq Calculate ΔG∘ using this relationship and the equilibrium constant (Keq) obtained in Part A at T=298K:Keq=1.92×1026 Express the Gibbs free energy (ΔG∘) in joules to three significant figures.
Keq = 1.92×1026 E∘cell=RT/nF* lnKeq B) ΔG∘ = −1.50×10^5 J The Gibbs free energy (ΔG∘) can also be calculated using the equation ΔG∘=−nFE∘cell. (Reaction is spontaneous)
Keq equation for 6CO2 (g) + 6H2O (l) = C6H12O6 (s) + 6O2 (g)
Keq= [O2]^6/ [CO2]^6 *do not include (s) or (l)
Methanol (CH3OH) can be made by the reaction of CO with H2: CO(g)+2H2(g)⇌CH3OH(g) The enthalphy change for the reaction is -90.7 kJ. To maximize the equilibrium yield of methanol, would you use a high or low temperature?
Low Temperature *The reaction is exothermic, so if you added heat it would cause a left shift, and you want to create a right shift
2Na (s) + Cl2 (g) = 2NaCl (s) What is the oxidation, reduction, oxidizing agent, and reducing agent What are the half reactions?
Oxidation: Na= Na^+1 + 1e^- Reduction: Cl + 2e^- = 2Cl Na is oxidized by Cl2 (Cl2 is the oxidizing agent) Cl is reduced by Na (Na is the reducing agent or reductant)
For the given reactions, classify the reactants as the reducing agent, oxidizing agent, or neither: N2 + 3H2 → 2NH3 2S + 3O2 → 2SO3 3S^2− + 14H^+ + Cr2O72− → 3S +2Cr^3+ + 7H2O
Oxidizing Agents: N2, O2, Cr2O72- Reducing Agents: H2, S, S2- Neither: H+
Which compound contains phosphorous in its highest oxidation state? PO43- PI3 P4 P2O2
PO4^3- P+4(-2)=-3 PI3 (P=3) P4 (P=0)
Endothermic VS Exothermic Graph
Products higher than reactants: Endothermic: DeltaH is positive *Separation of solvent/solute molecules *Exothermic: DeltaH is negative *Forming solvent/solute interactions *The shorter the overall graph, the faster the reaction
What is the rate law for a downward linear graph (m=-k), with ln[A] on Y-axis and time on x axis
Rate = K[A]
Consider the reaction 2H3PO4→P2O5+3H2O Using the information in the following table, calculate the average rate of formation of P2O5 between 10.0 and 40.0 s. Time (s) 0 10.0 20.0 30.0 40.0 50.0 [P2O5] (M) 0 2.20×10−3 5.20×10−3 7.00×10−3 8.20×10−3 8.80×10−3 Then determine the average rate of decomposition of H3PO4 between 10.0 and 40.0 s.
Rate of formation of P2O5 = 2.00×10−4 Ms Rate of decomposition of H3PO4 = 4.00×10−4 Ms (Rate of H3PO4=2(rate of P2O5)
Reaction Rate and Reaction Order
Rate: Delta[A]/Delta t= Delta[B]/Delta t Delta t = rate of disappearance of A or B Reaction Order: Rate= K[A]^m[B]^n Overall order = m+n
How will the following equilibria respond to an increased pressure caused by a decrease in volume? Reaction #1. 3NO (g) ⇌ N2O (g) + NO2 (g) Reaction #2. N2 (g) + O2 (g) ⇌ 2NO (g) Reaction #3. 2Cl2 (g) + 2H2O (g) ⇌ 4HCl (g) + O2 (g)
Reaction 1: Towards Products (right) Reaction 2: No influence (2=2) Reaction 3: Towards reactants (4<5) *Shift to side that has fewer molecules
What will be the result of an increase in pressure on the following reaction: 2CO2 (g)= 2CO (g) + O2 DeltaH = -514 KJ What will be the effect of temperature?
Reaction is exothermic, so heat is added to the right -Increase in pressure, moves to left -Decrease in pressure, moves to right -Temp: If you add temp, reaction becomes more endothermic, less exothermic, and shifts to the left -If you decrease heat, reaction becomes more negative, more exo, moves right -In endothermic reaction (absorbs heat), heat added to reactants, DeltaH>0, and solubility increases with T *Shift towards direction of excess heat
Oxidation Rules
Rule 1: The oxidation number of an element in its free state = 0 (Also true for diatomic elements) -Mg=0,H2=0, C=0 Rule 2: The oxidation number of a monatomic (one-atom) ion is the same as the charge on the ion -Mg^2+=+2, Na^+=+1, O^2-=-2 Rule 3: The sum of all oxidation numbers in a neutral compound is zero. The sum of all oxidation numbers in a polyatomic (many-atom) ion is equal to the charge on the ion. Rule 4: The oxidation number of an alkali metal (IA family) in a compound is +1; the oxidation number of an alkaline earth metal (IIA family) in a compound is +2. Rule 5: The oxidation number of oxygen in a compound is usually -2. If, however, the oxygen is in a class of compounds called peroxides (H2O2), then the oxygen has an oxidation number of -1. If the oxygen is bonded to fluorine, the number is +1. Rule 6: The oxidation state of hydrogen in a compound is usually +1. Rule 7: The oxidation number of fluorine is always -1. Chlorine, bromine, and iodine usually have an oxidation number of -1, unless they're in combination with an oxygen or fluorine. -In HF=-1, H=0 because F=-1
Questions
Slide 4: Why is the oxidizing agent FeO not just Fe
What change will be caused by addition of a small amount of HCl to a solution containing fluoride ions and hydrogen fluoride?
The concentration of fluoride ion will decrease and the concentration of hydrogen fluoride will increase.
Enthalpy Change
The enthalpy change of a reaction is the difference in energy between the reactants and the products: ΔH=Eproducts−Ereactants
Standard Reduction Potentials
The standard reduction potential for a substance indicates how readily that substance gains electrons relative to other substances at standard conditions. The more positive the reduction potential, the more easily the substance gains electrons.
A diagram represents a system that would have to shift to the left to establish equilibrium if:
There are more products/ fewer reactants
Transition States and Intermediates on Graphs
Transition States: Mountain Peaks Intermediates: Valleys *If the end is lower than the beginning of the graph, Enthalpy is negative
Calculate the freezing point of a solution prepared by dissolving 190 grams of a non-electrolyte solute ( i=1) with a formula weight of 148 g/mol in 850 grams of benzene. Kf=5.12 degC*kg/mol Normal freezing point of benzene is 5.5 degC Automobiles use antifreeze (ethylene glycol or CH2(OH)CH2(OH)) a non-volatile electrolyte in water to prevent engine damage from water freezing. Calculate the change in the freezing point of a 5.37 m solution of ethylene glycol in water. The freezing point depression constant of water is 1.86 degC/m
Use deltaT=-iKfm -(5.12 degCkgmol)*(190g/148g)/.85kg=-7.73 Tf=5.5degC-7.73degC=-2.23degC Answer: -2.23 degC Use deltaT= -iKfm = -11.865.37m Tf=0 degC-10 degC= -10 degC Answer= -10 degC
If acetic acid is the only acid that vinegar contains (Ka=1.8×10−5), calculate the concentration of acetic acid in the vinegar. A particular sample of vinegar has a pH of 2.95.
[HC2H3O2] = 7.1×10−2 M Ka = 1.8x10^-5 = [H+][A-]/[HA] [H+] = 10^-2.95 = .001122 1.8x10^-5 = (.001122)^2 / ([HA] - .001122)
2NH3 (g) ⇌ N2 (g) + 3H2 (g) Le Châtelier's principle predicts that the moles of H2 in the reaction container will increase with _____.
a decrease in the total pressure (T constant)
Indicate whether ΔG increases, decreases, or does not change when the partial pressure of H2 is increased in each of the following reactions. (a) N2(g)+3H2(g)→2NH3(g) (b) 2HBr(g)→H2(g)+Br2(g) (c) 2H2(g)+C2H2(g)→C2H6(g)
a) Decreases b) Increases c) Decreases
A scuba diver's tank contains 0.29kg of O2 compressed into a volume of 2.3 L. a. 0.29kg of O2 are how many moles? b. What is the pressure inside the tank at 9 oC?
a. 9.06 moles b. 91 atm
What is the solubility of 0.3 M HF if Ka of HF= 7.2*10^-4 HF (aq)+H2O (l) = F- (aq) + H3O+ (aq) What is he solubility of .3M HF in the presence of .1M KF?
pH = 1.83 ICE table 7.2*10^-4 = x^2/.3 pH= 2.67 7.2*10^-4 = .1X/.3 x= amount of HF that dissociates
What is the pH of a .10M solution of HCHO2 if Ka=1.8*10^-4? HCHO2= [H+] + CHO2^-
pH = 2.37 1.8*10^-4 = x^2/.10 x=.0042 -log(.0042)= 2.37
What is pH of .10 M solution of HCHO2 (Ka= 1.8*10^-4) HCHO2 = H+ + CHO2-
pH = 2.37 1.8*10^-4=x^2/.10
Ka of HClO=3*10^-8. What is pH of .34 M NaClO (weak base)?
pH= 10.5 1.010^-14/310^-8=3.33*10^-7 = Kb 3.33*10^-7=x^2/.34 = 3.37 -log(3.37)=3.47 pOH
NH4^+ has Ka=5.5*10^-10. Calculate pH of .629M solution of NH3 NH3 + H2O (l)= NH4^+ + OH^-
pH= 11.5 Kb= 1.8*10^-5=x^2/.629 x=.00336M OH^- -log(.00336) = 2.47 pOH
What is the pH of a buffer mixture made of 0.12 M acetic acid (CH3CO2H or HOAc) and 0.1 M sodium acetate (NaCH3CO2 or NaOAc)? Kb for acetate = 5.6 x 10-10 HOAc (aq) + H2O (l) = OAc- (aq) + H3O+ (aq)
pH= 4.7 Ka = 1.8*10^-5 = [OAc−][H3O+]/(HOAc) Henderson-Hasselbalch Equation pH = pKa + log[base]/[acid] pH=-log(1.8×10−5) + log (0.1/0.12) = 4.74 + (-0.079) = 4.7
Consider the reaction A+2B⇌C whose rate at 25 ∘C was measured using three different sets of initial concentrations as listed in the following table: Trial [A](M) [B](M) Rate(M/s) 1 0.10 0.050 6.0×10−4 2 0.10 0.100 1.2×10−3 3 0.20 0.050 2.4×10−3 What is the rate law for this reaction? Calculate the initial rate for the formation of C at 25 ∘C, if [A]=0.50M and [B]=0.075M.
rate = k[A]2[B] initial rate = 2.3×10−2 M/s (Calculated after determining that k = 1.2 M−2⋅s−1
2NO2(g)+F2(g)⇌2NO2F(g) The reaction is first order in F2 and second order overall. What is the rate law? If the concentration of NO2 was increased by half and the concentration of F2 was quadrupled, by what factor would the reaction rate increase?
rate=k[NO2][F2] 6: If the initial concentrations are [NO2]=x and [F2]=y, the reaction rate is rate=kxy the new rate would be new rate=k(1.5x)(4y)=6kxy 6kxy/kxy=6
Arrange the following aqueous solutions, each 10% by mass in solute, in order of decreasing boiling point: glucose (C6H12O6), sucrose (C12H22O11), sodium nitrate (NaNO3).
∆T = Kb x m x i kb is a constant for the solvent. kb for water is .512 C / molal m = molality of the solute = moles solute / kg solvent Assume 100 g solution, which means 10% x 100 = 10 g is solute and 90 g = 0.090 kg is solvent glucose: moles = 10 / 180 = 0.056 moles molality = 0.056 moles / 0.09 kg = 0.617 molal i = 1 m x i = 0.617 sucrose: moles = 10 / 342.3 = 0.029 moles molality = 0.029 moles / 0.09 kg = 0.324 molal i = 1 m x i = 0.324 Highest boiling point: Sodium Nitrate Lowest Boiling point: Sucrose
What is the value of ΔGo (in kJ/mol) for the following reaction 25.0 oC? Al (s) + Ag+ (aq) = Ag (s) + Al3+ (aq) Eo = + 2.46 V
- 712 kJ/mol ΔGo = - 3 x 96,500 J/V/mol x (+2.46 V)
Standard Entropy of Reaction Notes
-Measure of disorder/Reflects the degree of randomness/disorder -Molecular systems tend to move spontaneously to a state of maximum randomness or disorder. -The large increase in entropy upon mixing drives the formation of most solutions -As a state function, entropy change, ΔS, depends only on initial and final states. ΔS has a positive value when disorder increases and a negative value when disorder decreases. -The following conditions usually result in an increase in entropy: -A change of phase: solid→liquid→gas, -An increase in the number of gas molecules -A solid dissolving to form a solution. -Increase in volume 1. Unlike enthalpies of formation, standard molar entropies of elements at the reference temperature of 298 K are not zero. 3. Standard molar entropies generally increase with increasing molar mass. 4. Standard molar entropies generally increase with an increasing number of atoms in the formula of a substance.
When do gasses behave most ideally? Under which conditions would a gas behave LEAST ideally?
Low pressure high temperature High pressure and low temperature (Gasses don't like to be cold)
