115 Sample Exam 1

CHM-115-A Sample Exam 1

Copyright by James P. Birk 1

1. The following reactionC(s) + CO2(g) → 2CO(g)

is spontaneous only at temperatures in excess of 1100 K. From this information,we can conclude that

a. ∆Ηο > 0 and ∆So < 0b. ∆Ho < 0 and ∆So < 0c. ∆Ho > 0 and ∆So > 0d. ∆Ho < 0 and ∆So > 0e. ∆Go < 0 at all temperatures

2. Calculate ∆Go of formation, in kJ/mol, for H3PO4.4P(s) + 5O2(g) → P4O10(s) ∆G° = -269.8 kJ/molH2O(l) → H2(g) + ½O2(g) ∆G° = 237.2 kJ/molP4O10(s) + 6 H2O(l) → 4H3PO4(l) ∆G° = 630.2 kJ/molP(s) + 3/2 H2(g) + 2O2(g) → H3PO4(l) ∆G°f = ?

a. -1063b. -265.7c. 1063d. 265.7e. -123.0

3. Which of the following reactions has the largest positive molar entropy change?a. H2O(s) → H2O(g)b. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)c. N2(g) + 3H2(g) → 2NH3(g)d. PCl5(g) → PCl3(g) + Cl2(g)e. KClO4(s) + 4C(s) → KCl(s) + 4CO(g)

4. Which quantity has a value of zero for an element in its standard state?a. ∆Ho

fb. So

c. ∆Gof

d. both a and ce. all of a, b, and c

5. When ammonium nitrate dissolves in water, the solution becomes cold. We canconclude the following:

a. ∆Ho is positive and ∆So is positiveb. ∆Ho is positive and ∆So is negativec. ∆Ho is negative and ∆So is negatived. ∆Ho is negative and ∆So is positivee. ∆Ho is positive and ∆So is zero

Answers

1. c

2. b

3. e

4. d

5. a



6. Thermodynamics is applied to learn about a reaction�sa. pathwayb. mechanismc. stoichiometryd. ratee. spontaneity

7. In aqueous solution, iodine reacts with acetone as represented by the followingequation:

I2 + CH3COCH3 → CH3COCH2I + H+ + I-

The experimental rate law isRate = k[H+][CH3COCH3]

According to the information above, an increase in the iodine concentration haswhat effect on the reaction?

a. It increases ithe value of the equilibrium constant.b. It decreases the value of the equilibrium constant.c. It increases the rate of the reaction.d. It decreases the rate of the reaction.e. It does not affect the rate of the reaction.

8. At a constant temperature, which of the following would not affect the rate of agiven chemical reaction?

a. the magnitude of ∆Hb. the size of solid reactant particlesc. the reaction temperatured. the concentration of one or more reactantse. a catalyst

9. Identify an intermediate in the following mechanism. O3(g) = O2(g) + O(g) (fast) O(g) + O3(g) → 2O2(g) (slow)a. O(g)b. O3(g)c. O2(g)d. O2(g) and O(g)e. O3(g) and O2(g)

10. A first-order reaction has a rate constant of 0.021 s-1. The half-life for thisreaction is

a. 48 sb. 0.030 sc. 33 sd. 0.021 se. Not enough data is provided for this calculation.

6. e

7. e

8. a

9. a

10. c



11. Hypochlorite ion oxidizes iodide ion in aqueous solution as represented by theequation:

OCl- + I- → OI- + Cl-

The rate of formation of hypoiodite ion (OI-) is given by the rate lawRate = k[I-][OCl-]/[OH-]

The overall reaction order isa. 0b. 1c. 2d. 3e. k[I-][OCl-]/[OH-]

12. The following data were measured for the reaction: SO2(g) + 2Cl2(g) → SOCl2(g) + Cl2O(g)

Experiment [SO2](M) [Cl2](M) Initial Rate(M/s)1 0.100 0.100 0.252 0.200 0.100 0.503 0.200 0.200 2.004 0.300 0.400 ?

What is the missing value of the initial rate for experiment 4?a. 0.75b. 1.00c. 3.00d. 9.00e. 12.0

13. In a chemical reaction at constant temperature, the addition of a catalysta. affects the equilibrium constant.b. increases the fraction of molecules with high kinetic energy.c. provides an alternate reaction pathway with a different activation energy.d. decreases the energy released in the chemical reaction.e. increases the concentration of the products at equilibrium.

11. b

12. e

13. c



14. Consider the following energy diagram for a chemical reaction. The lowerdashed curve could represent

a. the reverse reaction.b. the same reaction in the presence of a catalyst.c. the same reaction at lower temperature.d. the same reaction at higher temperature.e. an intermediate in the reaction.

15. If the rate of a reaction increases by a factor of 64 when the concentration ofreactant increases by a factor of 4, the order of the reaction with respect to thisreactant is

a. 16b. 2c. 4d. 3e. 1

16. To determine whether the data available corresponds to a second-order ratelaw, a plot of which variables will yield a straight line?

a. ln [A] vs tb. ln [A] vs 1/tc. [A] vs td. [A]2 vs te. 1/[A] vs t

17. The position of equilibrium would not be appreciably affected by changes inthe volume of the container for

a. N2(g) + O2(g) = 2NO(g)b. N2(g) + 3H2(g) = 2NH3(g)c. H2O2(l) = H2O(l) + ½O2(g)d. P4(s) + 6Cl2(g) = 4PCl3(l)e. H2(g) + I2(s) = 2HI(g)

14. b

15. d

16. e

17. a



18. Consider the following reaction:N2O4(g) = 2NO2(g) ∆H = +58.2 kJ

What will cause an increase in the concentration of NO2 at equilibrium?a. The NO2 concentration will remain constant becaue it is equilibrium.b. an increase in temperaturec. an increase in pressured. a decrease in volumee. adding a catalyst

19. The equilibrium constant Kc = 0.00450 at 700 K for the reaction2HBr(g) = H2(g) + Br2(g)

What is the concentration of HBr at equilibrium if the initial concentrations are[HBr]o = 0.460 M, and [H2]o = [Br2]o = 0 M?

a. 0.00450b. 0.0671c. 0.259d. 0.406e. 0.208

20. Which one of the following statements is true regarding chemical equilibrium?a. Chemical equilibrium can only be attained at high temperatures.b. Chemical equilibrium can only be attained starting from the reactant sideof the equilibrium.c. At equilibrium, the reactant and product concentrations show no furtherchange with time.d. At equilibrium, the rate of the forward reaction is always greater than therate of the reverse reaction.e. At equilibrium, the product concentrations increase slightly with time.

21. If the ratio of the reaction quotient to the equilibrium constant, Q/K, is less than1,

a. more products are formed.b. the direction of reaction cannot be predicted.c. the system is at equilibrium.d. more reactants are formed.e. no net change occurs.

22. At a certain temperature, a vessel contains 0.980 M NH3(g), 1.53 M H2(g), and0.510 M N2(g) in a state of equilibrium. Calculate a value of Kc for the followingreaction:

N2(g) + 3H2(g) = 2NH3(g)a. 1.26b. 0.837c. 3.02d. 0.526e. 1.96

18. b

19. d

20. c

21. a

22. d



23. Consider the following reactionCaO(s) + CO2(g) = CaCO3(s)

The equilibrium constant expression isa. K = [CaCO3]/[CaO]b. K = [CaO][CO2]/[CaCO3]c. K = 1/[CO2]d. K = [CO2]e. K = [CaCO3]/[CaO][CO2]

24. For the reaction, MgCl2(s) + ½O2(g) = MgO(s) + Cl2(g), K = 2.98.For the reaction, 2Cl2(g) + 2MgO(s) = 2MgCl2(s) + O2(g), K is

a. 1.73b. 0.113c. -8.88d. 0.579e. 0.336

25. The following figure represents a set of initial conditions for the followingreaction,

with K = 9. Select the molecular picture that shows what the system looks likewhen the barrier separating the reactants is removed and the system reachesequilibrium.

a. b.

c. d.

e.

23. c

24. b

25. d

Documents

115 Sample Exam 1