Chemistry 5070 · O Level · Reversible reactions and equilibrium

Reversible reactions and equilibrium — practice question

Nitrogen monoxide combines with oxygen to produce nitrogen dioxide. If this reaction is examined in a closed system, dynamic equilibrium is reached. $\text{2NO}(g) + \text{O}_2(g) \rightleftharpoons \text{2NO}_2(g)$
(a)[1]

Explain why a closed system is necessary if dynamic equilibrium is to be set up.

(b)[2]

The pressure of the equilibrium mixture is lowered. The temperature of the equilibrium mixture remains constant. Predict and explain what, if anything, happens to the composition of the equilibrium mixture.

(c(i))[1]

The temperature of the equilibrium mixture is lowered. The pressure of the equilibrium mixture is held constant. Suggest why the equilibrium position shifts to the right.

(c(ii))[2]

Explain why the reaction rate falls.

(d)[1]

Draw the ‘dot-and-cross’ diagram for a molecule of O$_2$. Show only the outer shell electrons.

(e)[1]

Nitrogen dioxide reacts with water to produce nitric acid, HNO$_3$, and nitrous acid, HNO$_2$. Write an equation for this reaction.

(f)[2]

Nitric acid is a strong acid whereas nitrous acid is a weak acid. Describe the difference between a strong acid and a weak acid.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: Reactants and products cannot escape from the system

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