Q: A reaction mechanism is: 1st step: $$\mathrm{A \rightleftharpoons B} ($$very fast) 2nd step: $$\mathrm{B + C \rightarrow D} ($$slow) 3rd step: $$\mathrm{D \rightarrow 2E} ($$fast) What is the rate law for this reaction?

$$\text{rate} = k[\mathrm{A}][\mathrm{C}]$$

Q: The half-life for the decay of radium is $$1620$$ years. What is the rate constant for this first-order process?

$$4.28 \times 10$$^{-4}$$\ \mathrm{yr}^{-1}$$

Q: What data should be plotted to show that experimental concentration data fits a second-order reaction?

$$1/[\text{reactant}] vs. $$time

Question 1

A reaction has $$\Delta H = +75\ \mathrm{kJ}$$ and $$\Delta S = -120\ \mathrm{J/K}. $$Which statement about the spontaneity of this reaction is correct?

Accepted Answer

The reaction is nonspontaneous at all temperatures.

Question 2

Given the reaction $$\mathrm{N_2H_4(l) + H_2$(g) \rightarrow 2 NH_3$(g)}$$ with $$S^\circ$$ values: $$\mathrm{N_2H_4(l)} = 121.2\ \mathrm{J/(mol\cdot K)}$$, $$\mathrm{H_2$(g)} = 130.7\ \mathrm{J/(mol\cdot K)}$$, $$\mathrm{NH_3$(g)} = 192.8\ \mathrm{J/(mol\cdot K)}$$, calculate $$\Delta S^\circ_{rxn}.$$

Accepted Answer

$$+133.7\ \mathrm{J/K}$$

Question 3

Which law of thermodynamics states that for any spontaneous process, the entropy of the universe increases?

Accepted Answer

Second Law

Question 4

Calculate $$\Delta G^\circ_{rxn}$$ for the reaction $$2\ \mathrm{$$HNO_3$$(aq)} + \mathrm{NO(g)} \rightarrow 3\ \mathrm{NO_2$(g)} + \mathrm{H_2O(l)}$$ using the following data: $$\Delta G^\circ_f (kJ/$$mol): $$\mathrm{$$HNO_3$$(aq)} = -110.9$$, $$\mathrm{NO(g)} = 87.6$$, $$\mathrm{NO_2$(g)} = 51.3$$, $$\mathrm{H_2O(l)} = -237.1.$$

Accepted Answer

$$+51.0\ \mathrm{kJ}$$

Question 5

For the reaction $$\mathrm{SO_3$(g) + H_2O(g) \rightarrow H_2SO_4(l)}$$ with $$\Delta G^\circ = -90.5\ \mathrm{kJ} at$$ $$298\ \mathrm{K}$$, what is the equilibrium constant $$K$$?

Accepted Answer

$$7.31 	imes 10$$^{15}$$

Question 6

Using Hess's Law and the following reactions, calculate $$\Delta G^\circ_{rxn}$$ for $$\mathrm{CO(g) \rightarrow C(s) + \frac{1}{2} O_2$(g)}$$:

$$\mathrm{CO_2$(g) \rightarrow C(s) + O_2$(g)}$$, $$\Delta G^\circ_{rxn} = +394.4\ \mathrm{kJ}$$

$$\mathrm{CO(g) + \frac{1}{2} O_2$(g) \rightarrow CO_2$(g)}$$, $$\Delta G^\circ_{rxn} = -257.2\ \mathrm{kJ}$$

Accepted Answer

$$+137.2\ \mathrm{kJ}$$

Question 7

Above what temperature does the reaction $$\mathrm{N_2$(s) + 3 H_2$(g) \rightarrow 2 NH_3$(g)}$$ ($$\Delta H = -92.22\ \mathrm{kJ}$$, $$\Delta S = -198.75\ \mathrm{J/K}) $$become nonspontaneous?

Accepted Answer

$$464\ \mathrm{K}$$

Question 8

Which of the following best describes the process $$\mathrm{H_2O(l) \rightarrow H_2O(g)} in $$terms of enthalpy and entropy?

Accepted Answer

Positive $$\Delta H$$ and positive $$\Delta S$$

Question 9

If the equilibrium constant $$K \gg 1$$ for a chemical reaction, what does this indicate about the reaction?

Accepted Answer

The forward reaction is favored.

Question 10

For the reaction $$2\ \mathrm{SO_2$(g)} + \mathrm{O_2$(g)} \rightleftharpoons 2\ \mathrm{SO_3$(g)}$$, what is $$\Delta n$$ when relating $$K_c to$$ $$K_p$$?

Accepted Answer

$$-1$$

Question 11

Express the equilibrium constant $$K$$ for the reaction $$\mathrm{P_4$(s) + 5 O_2$(g) \rightleftharpoons P_4O_{10}(s)} in $$terms of concentrations.

Accepted Answer

$$K = [O_2$]^{-5}$$

Question 12

Given the equilibrium concentrations $$[\mathrm{N_2$}]_{eq} = 1.5\ \mathrm{M}$$, $$[\mathrm{H_2$}]_{eq} = 1.1\ \mathrm{M}$$, $$[\mathrm{NH_3$}]_{eq} = 0.47\ \mathrm{M}$$ for the reaction $$\mathrm{N_2$(g) + 3 H_2$(g) \rightleftharpoons 2 NH_3$(g)}$$, what is $$K_c$$?

Accepted Answer

$$0.11$$

Question 13

A reaction mixture initially contains $$2.8\ \mathrm{M}$$ $$\mathrm{H_2O}$$ and $$2.6\ \mathrm{M}$$ $$\mathrm{SO_2$}$$ for the reaction $$2\ \mathrm{H_2O(g)} + 2\ \mathrm{SO_2$(g)} ightleftharpoons 2\ \mathrm{H_2S(g)} + 3\ \mathrm{O_2$(g)}. If$$ $$K_c = 1.3 	imes 10$$^{-6}$$, what is the equilibrium concentration of $$\mathrm{H_2S}$$?

Accepted Answer

$$0.12\ \mathrm{M}$$

Question 14

For the reaction $$\mathrm{C_3H_8(g) + 5 O_2$(g) \rightleftharpoons 3 CO_2$(g) + 4 H_2O(l)} at $$equilibrium, what effect will reducing the volume have on the system?

Accepted Answer

The reaction will shift to the right in the direction of products.

Question 15

Given the rate law $$	ext{Rate} = k[\mathrm{NO}][\mathrm{O_3$}]$$ for the reaction $$\mathrm{NO(g) + O_3$(g) ightarrow NO_2$(g) + O_2$(g)}$$, what is the overall order of the reaction?

Accepted Answer

2nd order

Question 16

A reaction mechanism is:
1st step: $$\mathrm{A \rightleftharpoons B} ($$very fast)
2nd step: $$\mathrm{B + C \rightarrow D} ($$slow)
3rd step: $$\mathrm{D \rightarrow 2E} ($$fast)
What is the rate law for this reaction?

Accepted Answer

$$	ext{rate} = k[\mathrm{A}][\mathrm{C}]$$

Question 17

Which of the following will NOT affect the rate of a chemical reaction?

Accepted Answer

None of the above; all affect the rate.

Question 18

The half-life for the decay of radium is $$1620$$ years. What is the rate constant for this first-order process?

Accepted Answer

$$4.28 	imes 10$$^{-4}$$\ \mathrm{yr}^{-1}$$

Question 19

What data should be plotted to show that experimental concentration data fits a second-order reaction?

Accepted Answer

$$1/[	ext{reactant}] vs. $$time

General Chemistry II: Thermodynamics, Equilibrium, and Kinetics Practice Exam Guidance

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