Consider the reversible reaction N_2O_4(g) 2 , NO_2(g) occurring in a rigid container…

CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)

Problem

Consider the reversible reaction

\mathrm{N_2O_4(g)} \leftrightharpoons 2\,\mathrm{NO_2(g)}

occurring in a

1.00\,\text{L}

rigid container at constant temperature. The elementary rate expressions for the two opposing processes are

\text{Rate}(\mathrm{N_2O_4 \rightarrow 2\,NO_2}) = k_1\,[\mathrm{N_2O_4}]

\text{Rate}(2\,\mathrm{NO_2 \rightarrow N_2O_4}) = k_2\,[\mathrm{NO_2}]^2

where concentrations are in

\text{mol}\cdot\text{L}^{-1}

. At

298\,\text{K}

, the rate constants have the values

k_1 = 1.5\times10^{-2}\,\text{s}^{-1}

and

k_2 = 3.0\times10^{-3}\,\text{L}\,\text{mol}^{-1}\,\text{s}^{-1}.

Initially, the container holds

0.0200\,\text{mol}

\mathrm{N_2O_4(g)}

and no

\mathrm{NO_2(g)}

. The system is allowed to evolve until it reaches a state for which the forward and reverse rates are equal. At that point, an external device instantly injects an additional

0.0100\,\text{mol}

\mathrm{NO_2(g)}

into the container (volume unchanged) without otherwise disturbing temperature or pressure. Respond to the following prompts. (a) Before the injection of extra

\mathrm{NO_2(g)}

, calculate the equilibrium concentrations of

\mathrm{N_2O_4(g)}

and

\mathrm{NO_2(g)}

. Show all steps clearly. (b) Immediately after the

0.0100\,\text{mol}

injection, determine the new concentrations of

\mathrm{N_2O_4(g)}

and

\mathrm{NO_2(g)}

that exist before any further reaction occurs. (c) Using the rate expressions and the concentrations from part (b), compute the instantaneous forward and reverse rates just after the injection. (d) Identify the net direction in which the reaction will proceed immediately after the injection and justify your conclusion quantitatively.

Related theory

Browse the problem library