Question 3

This question is about a homogeneous chemical equilibrium in aqueous solution.

\text{P(aq)} + 3\text{Q(aq)} \rightleftharpoons 2\text{R(aq)} + 3\text{S(aq)}

A $cm340.0\text{ cm}^3$ sample of a solution of $P\text{P}$ is added to a $cm360.0\text{ cm}^3$ sample of a solution of $Q\text{Q}$ . The mixture is allowed to reach equilibrium.

The amounts in the equilibrium mixture are:

$mol\text{P} = 0.0120\text{ mol}$
$mol\text{Q} = 0.0360\text{ mol}$
$mol\text{R} = 0.0160\text{ mol}$
$mol\text{S} = 0.0240\text{ mol}$

Calculate the amount, in moles, of $Q\text{Q}$ before the reaction with $P\text{P}$ . Use your answer to calculate the concentration, in $dm−3\text{mol dm}^{-3}$ , of $Q\text{Q}$ in the initial $cm360.0\text{ cm}^3$ sample.

Give the expression for the equilibrium constant, $KcK_{\text{c}}$ . Calculate the value of $KcK_{\text{c}}$ , and deduce its units.

Explain why the amount of $S\text{S}$ increases when water is added to the equilibrium mixture.