Q: Consider the reaction: $$\mathrm{A}(g) + \mathrm{B}(g) \rightleftharpoons \mathrm{C}(g). $$The equilibrium concentrations are $$[\mathrm{A}] = 0.10\ \mathrm{mol/L}$$, $$[\mathrm{B}] = 0.20\ \mathrm{mol/L}$$, and $$[\mathrm{C}] = 0.40\ \mathrm{mol/L}. $$What is the value of the equilibrium constant $$K$$?

$$K = \dfrac{0.40}{0.10 \times 0.20}$$

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 enthalpy change ($$\Delta H). $$Which of the following statements is TRUE about this reaction?

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

Question 3

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

Accepted Answer

Dissolving table salt in water.

Question 4

Given the following reaction: $$2\ \mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 2\ \mathrm{H}_2\mathrm{O}(g)$$, and the following average bond dissociation energies: $$\mathrm{H}-\mathrm{H} = 103\ \mathrm{kcal/mol}$$, $$\mathrm{O}=\mathrm{O} = 119\ \mathrm{kcal/mol}$$, $$\mathrm{O}-\mathrm{H} = 112\ \mathrm{kcal/mol}$$, calculate the enthalpy change ($$\Delta H) $$for the reaction.

Accepted Answer

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

Question 5

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

Accepted Answer

It provides an alternative pathway with a lower activation energy.

Question 6

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 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 more $$\mathrm{NH}_3$$)?

Accepted Answer

Increasing the pressure by decreasing the volume.

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 $$[\mathrm{A}] = 0.10\ \mathrm{mol/L}$$, $$[\mathrm{B}] = 0.20\ \mathrm{mol/L}$$, and $$[\mathrm{C}] = 0.40\ \mathrm{mol/L}. $$What is the value of the equilibrium constant $$K$$?

Accepted Answer

$$K = \dfrac{0.40}{0.10 	imes 0.20}$$

Question 10

A reaction mixture is at equilibrium. If the concentration of a reactant is increased, what will happen according to Le Châtelier’s principle?

Accepted Answer

The equilibrium will shift to produce more products.

Question 11

Which of the following best describes the effect of increasing temperature on an exothermic equilibrium reaction?

Accepted Answer

The equilibrium shifts toward the reactants.

Question 12

Which of the following is TRUE about the activation energy of a reaction?

Accepted Answer

A lower activation energy means more molecules have enough energy to react.

Question 13

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 14

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

Accepted Answer

Adding a catalyst.

Question 15

In a biological system, a metabolic pathway often prevents equilibrium from being reached by:

Accepted Answer

Continuously removing a product as it is formed.

Question 16

Which of the following statements about the free energy change ($$\Delta G) of a $$reaction is CORRECT?

Accepted Answer

$$\Delta G$$ tells us whether a reaction is spontaneous.

Question 17

A reaction has $$\Delta H \u003c 0$$ and $$\Delta S \u003c 0. $$Under what conditions will this reaction be spontaneous?

Accepted Answer

At low temperatures only.

Question 18

Which of the following best describes the law of conservation of energy as it applies to chemical reactions?

Accepted Answer

Energy is neither created nor destroyed; it is transferred between system and surroundings.

Question 19

A reaction is carried out at constant pressure and releases 50 kJ of heat. What is the sign and value of $$\Delta H$$ for this reaction?

Accepted Answer

$$\Delta H = -50\ \mathrm{kJ}$$

Question 20

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

Accepted Answer

Increasing the concentration of reactants.

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

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