Question 1:

What is chemical equilibrium?

Explanation: The correct answer is B) The point at which the rate of the forward reaction equals the rate of the reverse reaction. Chemical equilibrium is a state in a reversible reaction where the concentrations of reactants and products no longer change over time. At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction.

Question 2:

According to Le Chatelier's principle, what happens when a stress is applied to a system at equilibrium?

Explanation: The correct answer is A) The equilibrium shifts to relieve the stress and restore equilibrium. According to Le Chatelier's principle, when a stress, such as a change in concentration, pressure, or temperature, is applied to a system at equilibrium, the equilibrium position will shift in a way that reduces the effect of the stress and reestablishes equilibrium.

Question 3:

How does an increase in temperature affect an exothermic reaction at equilibrium?

Explanation: The correct answer is B) It shifts the equilibrium towards the products. An increase in temperature favors the endothermic direction of a reaction. In an exothermic reaction, the reactants release heat, so an increase in temperature is considered as a stress. According to Le Chatelier's principle, the equilibrium will shift in the endothermic direction to absorb the additional heat, resulting in an increase in the concentration of products.

Question 4:

How does an increase in pressure affect a reaction involving gases at equilibrium?

Explanation: The correct answer is A) It shifts the equilibrium towards the side with fewer moles of gas. An increase in pressure is a stress on a system involving gases. According to Le Chatelier's principle, the equilibrium will shift in the direction that reduces the total number of gas molecules. This is achieved by favoring the side of the reaction with fewer moles of gas.

Question 5:

How does the addition of a catalyst affect the equilibrium of a chemical reaction?

Explanation: The correct answer is C) It has no effect on the equilibrium position. A catalyst is a substance that speeds up the rate of a chemical reaction without being consumed in the process. It does not affect the equilibrium position or the concentrations of reactants and products at equilibrium. A catalyst provides an alternative reaction pathway with a lower activation energy, enabling the reaction to reach equilibrium faster but without changing the position of the equilibrium.