Question 1

Which of the following statements best describes the difference between potential energy and kinetic energy in the context of chemical bonds?

Accepted Answer

Potential energy is stored in the attractive forces between atoms or ions, while kinetic energy is the energy of motion of particles.

Question 2

Which of the following reactions is exothermic?

Accepted Answer

$$\mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(l)}$$ with $$\Delta H = -213\ \mathrm{kcal/mol}$$

Question 3

Calculate the heat released (in kJ) when 0.35 mol of methane combusts, given $$\Delta H = -213\ \mathrm{kcal/mol}$$ for $$\mathrm{CH_4$}$$ combustion. ($$1\ \mathrm{kcal} = 4.184\ \mathrm{kJ})$$

Accepted Answer

$$-314\ \mathrm{kJ}$$

Question 4

Which of the following best explains why the thermite reaction is used to weld railroad tracks?

Accepted Answer

It is a strongly exothermic reaction that releases enough heat to melt iron.

Question 5

Given the reaction $$2\mathrm{H_2$} + \mathrm{O_2$} \rightarrow 2\mathrm{H_2O}$$, and the following bond dissociation energies: $$\mathrm{H-H} = 103\ \mathrm{kcal/mol}$$, $$\mathrm{O=O} = 119\ \mathrm{kcal/mol}$$, $$\mathrm{O-H} = 112\ \mathrm{kcal/mol}$$, calculate $$\Delta H$$ for the reaction.

Accepted Answer

$$-123\ \mathrm{kcal/mol}$$

Question 6

Which of the following changes will increase the rate of a chemical reaction?

Accepted Answer

Adding a catalyst

Question 7

Which of the following statements about entropy ($$S) is $$correct?

Accepted Answer

Entropy increases when a solid melts to a liquid.

Question 8

For the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, which change will shift the equilibrium to the right?

Accepted Answer

Increasing the concentration of $$\mathrm{N_2$}$$

Question 9

Which of the following is the correct equilibrium constant expression for the reaction $$\mathrm{H_2O(g) + CH_4$(g) \rightleftharpoons CO(g) + 3H_2(g)}$$?

Accepted Answer

$$K = \dfrac{[CO][H_2$]^3}{[H_2O][CH_4$]}$$

Question 10

A reaction has $$\Delta H = +50\ \mathrm{kJ}$$ and $$\Delta S = +200\ \mathrm{J/K}. At $$what temperature (in K) does the reaction become spontaneous? ($$\Delta G = \Delta H - T\Delta S)$$

Accepted Answer

$$T \u003e 250\ \mathrm{K}$$

Question 11

Which of the following best describes the effect of a catalyst on a chemical reaction?

Accepted Answer

It decreases the activation energy and increases the reaction rate.

Question 12

Which of the following scenarios will NOT affect the position of equilibrium for a chemical reaction?

Accepted Answer

Adding a catalyst

Question 13

For the reaction $$\mathrm{$$PCl_3$$(g) + Cl_2$(g) \rightleftharpoons $$PCl_5$$(g)}$$, the equilibrium concentrations are $$[$$PCl_3$$] = 7.2\ \mathrm{mol/L}$$, $$[Cl_2$] = 7.2\ \mathrm{mol/L}$$, $$[$$PCl_5$$] = 0.050\ \mathrm{mol/L}. $$What is the value of $$K$$?

Accepted Answer

$$K = 9.6 	imes 10$$^{-4}$$

Question 14

Which of the following best describes a spontaneous process?

Accepted Answer

A process that, once started, proceeds on its own without external influence.

Question 15

Which of the following changes will shift the equilibrium of the endothermic reaction $$\mathrm{N_2$(g) + O_2$(g) \rightleftharpoons 2NO(g)}$$ ($$\Delta H = +43\ \mathrm{kcal/mol}) to $$the right?

Accepted Answer

Increasing the temperature

Question 16

Which of the following is true about the relationship between activation energy ($$E_{act}) $$and reaction rate?

Accepted Answer

A lower activation energy means a faster reaction.

Question 17

Which of the following best describes the effect of increasing pressure on the equilibrium of the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$?

Accepted Answer

It shifts the equilibrium to the right, favoring fewer gas molecules.

Question 18

Which of the following is the correct expression for the free-energy change of a reaction?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Chemical Reactions: Energy, Rates, and Equilibrium – Study Guide

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