Reversible Reactions Quiz Questions And Answers

1. 2NH₃(g) <------> N₂(g) + 3H₂(g) ; Heat of reaction = +92 kJ
The amount of ammonia in the equilibrium mixture can be made larger by

Changing the catalyst.

Lowering the temperature.

Lowering the pressure.

Removing some of the hydrogen.

Lowering the temperature will shift the equilibrium towards the reactants side according to Le Chatelier's principle. Since the forward reaction is exothermic (heat of reaction = +92 kJ), decreasing the temperature will favor the endothermic direction to counteract the decrease in temperature. As a result, more ammonia will be produced to restore equilibrium, increasing the amount of ammonia in the mixture.

Explanation

Lowering the temperature will shift the equilibrium towards the reactants side according to Le Chatelier's principle. Since the forward reaction is exothermic (heat of reaction = +92 kJ), decreasing the temperature will favor the endothermic direction to counteract the decrease in temperature. As a result, more ammonia will be produced to restore equilibrium, increasing the amount of ammonia in the mixture.

2. When a reversible reaction reaches dynamic equilibrium at constant temperature,

The reaction stops.

Equal amounts of reactants and products are present.

The ratio of the product concentration to the reactant concentration is constant.

The products of the forward reaction stop reacting altogether.

When a reversible reaction reaches dynamic equilibrium at a constant temperature, it means that the rate of the forward reaction is equal to the rate of the reverse reaction. This implies that the concentrations of the reactants and products remain constant over time. At equilibrium, the ratio of the product concentration to the reactant concentration is constant, indicating that the reaction has reached a balance where the concentrations of the reactants and products are stable. Therefore, the correct answer is that the ratio of the product concentration to the reactant concentration is constant.

Explanation

When a reversible reaction reaches dynamic equilibrium at a constant temperature, it means that the rate of the forward reaction is equal to the rate of the reverse reaction. This implies that the concentrations of the reactants and products remain constant over time. At equilibrium, the ratio of the product concentration to the reactant concentration is constant, indicating that the reaction has reached a balance where the concentrations of the reactants and products are stable. Therefore, the correct answer is that the ratio of the product concentration to the reactant concentration is constant.

3. The equation shows the equilibrium between A, B and C.
A (g) + 2 B (g) <---> 2 C (g) ΔH = +150 kJ
How can the amount of B in the equilibrium mixture be increased?

Adding more of A

Lowering the temperature

Removing some of C

Increasing the pressure

Lowering the temperature will shift the equilibrium towards the reactants side to counteract the decrease in temperature. Since the forward reaction is exothermic (ΔH = +150 kJ), decreasing the temperature will favor the endothermic reaction, which is the reverse reaction. This will result in an increase in the concentration of B in the equilibrium mixture.

Explanation

Lowering the temperature will shift the equilibrium towards the reactants side to counteract the decrease in temperature. Since the forward reaction is exothermic (ΔH = +150 kJ), decreasing the temperature will favor the endothermic reaction, which is the reverse reaction. This will result in an increase in the concentration of B in the equilibrium mixture.

4. In which reaction will be amount of product be increased by decreasing the pressure?

2NO (g) + O2(aq) 2NO2 (g)

N2 (g) + 3H2 (g) 2NH3 (g)

2NO2 (g) N2O4 (g)

CH4 (g) + H2O (g) CO (g) + 3H2 (g)

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Explanation

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5. On 6 & 7.

In the Haber Process,

N₂(g) + 3H₂(g) <------> 2NH₃(g)

The following graph shows the effect of temperature and pressure on the yield.

Which of the following options does not explain why the yield increases when temperature decreases?

The system responds in a way so as to counteract the decreased temperature.

The system favours the forward reaction which is exothermic.

The system favours the forward reaction which is endothermic.

The system responds in a way in accordance with Le Chatelier's principle, replacing the heat lost by raising the temperature.

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Explanation

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6. The equation show the equilibrium between silver ions and iron(II) ions.
Ag⁺(aq) + Fe²⁺(aq)

<----> Ag(s) + Fe³⁺(aq) Which one of the following statements is not true for the above equilibrium?

At equilibrium, the rate of the forward reaction is equal to the rate of the backward reaction.

The concentration of all reactants and products are independent of the external pressure.

Addition of dilute hydrochloric acid to precipitate silver chloride would cause the equilibrium to shift to the left.

The yield of silver metal could be significantly increased by adding a catalyst.

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Explanation

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7. Which of the following options does not explain why the yield increases when pressure is increased?

The volume of gas molecules decreases in the forward reaction.

The number of moles of gas molecules increases in the forward reaction.

The position of equilibrium shifts to the right to favour the forward reaction.

An increase in pressure due to decreasing volume causes the reaction to shift to the side with the fewer moles of gas. This is because according to Le Chatelier's principle, when the pressure is increased, the system will try to decrease the pressure by shifting the equilibrium towards the side with fewer moles of gas. This explanation is supported by the fact that the volume of gas molecules decreasing in the forward reaction and the position of equilibrium shifting to the right to favor the forward reaction both contribute to an increase in yield when pressure is increased.

Explanation

An increase in pressure due to decreasing volume causes the reaction to shift to the side with the fewer moles of gas. This is because according to Le Chatelier's principle, when the pressure is increased, the system will try to decrease the pressure by shifting the equilibrium towards the side with fewer moles of gas. This explanation is supported by the fact that the volume of gas molecules decreasing in the forward reaction and the position of equilibrium shifting to the right to favor the forward reaction both contribute to an increase in yield when pressure is increased.