Q: Consider the reaction $$\mathrm{A}(g) + \mathrm{B}(g) \rightleftharpoons \mathrm{C}(g). $$The equilibrium concentrations are $$[A]=0.2\ \mathrm{mol/L}$$, $$[B]=0.2\ \mathrm{mol/L}$$, and $$[C]=0.4\ \mathrm{mol/L}. $$What is the value of the equilibrium constant $$K$$?

$$K = \dfrac{0.4}{0.2 \times 0.2} = 10$$

Question 1

Which of the following 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

A chemical reaction has a negative value for $$\Delta H. $$Which of the following statements is true about this reaction?

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

Question 3

Given 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 the enthalpy change $$\Delta H$$ for the reaction: $$2\ \mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2\ \mathrm{H}_2\mathrm{O}.$$

Accepted Answer

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

Question 4

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

Accepted Answer

Dissolving table salt in water.

Question 5

A reaction has $$\Delta H \u003e 0$$ and $$\Delta S \u003e 0. $$Under what conditions will this reaction be spontaneous?

Accepted Answer

At high temperatures only.

Question 6

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

Accepted Answer

It lowers the activation energy required for the reaction to occur.

Question 7

For the reversible reaction $$\mathrm{N}_2(g) + 3\ \mathrm{H}_2(g) \rightleftharpoons 2\ \mathrm{NH}_3(g)$$, which of the following changes will shift the equilibrium to the right (toward ammonia production) according to Le Châtelier’s principle?

Accepted Answer

Increasing the concentration of $$\mathrm{N}_2$$

Question 8

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 9

Consider the reaction $$\mathrm{A}(g) + \mathrm{B}(g) \rightleftharpoons \mathrm{C}(g). $$The equilibrium concentrations are $$[A]=0.2\ \mathrm{mol/L}$$, $$[B]=0.2\ \mathrm{mol/L}$$, and $$[C]=0.4\ \mathrm{mol/L}. $$What is the value of the equilibrium constant $$K$$?

Accepted Answer

$$K = \dfrac{0.4}{0.2 	imes 0.2} = 10$$

Question 10

A reaction has a large equilibrium constant ($$K \gg 1). $$What does this indicate about the position of equilibrium?

Accepted Answer

The reaction favors the products at equilibrium.

Question 11

Which of the following changes will NOT affect the position of equilibrium for a gaseous reaction?

Accepted Answer

Adding a catalyst

Question 12

A reaction mixture is at equilibrium. If the temperature is increased for an exothermic reaction, what will happen to the equilibrium position?

Accepted Answer

It will shift toward the reactants.

Question 13

Which of the following best describes the relationship between activation energy and reaction rate?

Accepted Answer

A lower activation energy leads to a faster reaction rate.

Question 14

A reaction has $$\Delta G \u003c 0$$ but occurs very slowly at room temperature. Which of the following best explains this observation?

Accepted Answer

The reaction has a high activation energy barrier.

Question 15

Which of the following scenarios is an example of a nonspontaneous process?

Accepted Answer

Water flowing uphill without external work.

Question 16

If the concentration of a product in a reversible reaction is continuously removed as it forms, what will happen to the reaction?

Accepted Answer

The reaction will never reach equilibrium.

Question 17

Which of the following best describes the effect of increasing the concentration of reactants on the rate of a chemical reaction?

Accepted Answer

It increases the frequency of collisions and usually increases the reaction rate.

Question 18

A reaction is endothermic and nonspontaneous at room temperature. Which of the following changes could make the reaction spontaneous?

Accepted Answer

Increase the temperature if $$\Delta S is $$positive.

Question 19

Which of the following statements about the law of conservation of energy is correct in the context of chemical reactions?

Accepted Answer

The total energy before and after a chemical reaction is the same; energy is neither created nor destroyed.

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

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