Question 1

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

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

During the combustion of methane, $$ \mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(l)} $$, the enthalpy change $$ (\Delta H)  is$$ $$ -213 \ \mathrm{kcal/mol} . $$How much heat (in kJ) is released when 0.50 mol of methane is completely combusted?

Accepted Answer

$$ -445.5 \ \mathrm{kJ} $$

Question 3

Which of the following statements about exothermic and endothermic reactions is correct?

Accepted Answer

Exothermic reactions release heat to the surroundings and have a negative $$ \Delta H .$$

Question 4

Given the reaction $$ 2H_2(g) + O_2$(g) \rightarrow 2H_2O(l) $$, and the following bond dissociation energies: $$ H-H = 103 \ \mathrm{kcal/mol} $$, $$ O=O = 119 \ \mathrm{kcal/mol} $$, $$ O-H = 112 \ \mathrm{kcal/mol} . $$What is the enthalpy change $$ (\Delta H) $$ for the reaction?

Accepted Answer

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

Question 5

Which of the following changes will increase the rate of a chemical reaction according to collision theory?

Accepted Answer

Adding a catalyst to the reaction.

Question 6

A reaction has $$ \Delta H = +50 \ \mathrm{kJ/mol} $$ and $$ \Delta S = +200 \ \mathrm{J/(mol \cdot K)} . At $$what minimum temperature (in K) will this reaction become spontaneous?

Accepted Answer

$$ 500 \ \mathrm{K} $$

Question 7

Which of the following best explains why a catalyst increases the rate of a chemical reaction?

Accepted Answer

A catalyst provides an alternative pathway with a lower activation energy.

Question 8

For the reaction $$ N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) $$, which of the following changes will shift the equilibrium to the right (toward more $$ NH_3$ ) $$according to Le Chatelier’s Principle?

Accepted Answer

Increasing the concentration of $$ N_2$ .$$

Question 9

Which of the following statements about chemical equilibrium is correct?

Accepted Answer

At equilibrium, the rates of the forward and reverse reactions are equal.

Question 10

Consider the reaction $$ 2NO_2(g) \rightleftharpoons 2NO(g) + O_2$(g) . If $$the volume of the reaction vessel is increased, what will happen to the equilibrium position?

Accepted Answer

The equilibrium will shift to the right, favoring $$ NO $$ and $$ O_2$ $$ formation.

Question 11

Which of the following is true about the value of the equilibrium constant $$ (K) $$ for a reaction?

Accepted Answer

A large $$ K $$ value ($$ K \u003e 1 ) $$indicates that products are favored at equilibrium.

Question 12

Which of the following scenarios represents an increase in entropy $$ (\Delta S \u003e 0) $$?

Accepted Answer

Smoke dispersing throughout a room.

Question 13

For the reaction $$ aA + bB \rightleftharpoons dD + nN $$, the equilibrium constant expression is:

Accepted Answer

$$ K = \frac{[D]^d [N]^n}{[A]^a [B]^b} $$

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

A reaction has $$ \Delta H = -100 \ \mathrm{kJ/mol} $$ and $$ \Delta S = -200 \ \mathrm{J/(mol \cdot K)} . At $$what temperature (in K) does the reaction become nonspontaneous?

Accepted Answer

$$ 500 \ \mathrm{K} $$

Question 16

Which of the following is NOT a way to increase the rate of a chemical reaction?

Accepted Answer

Decreasing the surface area of reactants.

Question 17

If the forward reaction in a reversible process is exothermic, what effect does increasing the temperature have on the equilibrium position?

Accepted Answer

It shifts the equilibrium toward the reactants.

Question 18

Which of the following statements about activation energy $$ (E_a)  is $$correct?

Accepted Answer

A lower activation energy means more molecules can react per unit time.

Question 19

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

Accepted Answer

A catalyst allows equilibrium to be reached more quickly without changing the equilibrium concentrations.

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

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