A mixture of and is sealed in a rigid container at 298 K

CHEMISTRY · Single correct · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)

Problem

A mixture of

\mathrm{NO}_{2}(g)

and

\mathrm{N}_{2}\mathrm{O}_{4}(g)

is sealed in a rigid container at 298 K, where the equilibrium constant for

2\,\mathrm{NO}_{2}(g)\rightleftharpoons\mathrm{N}_{2}\mathrm{O}_{4}(g)

K_{298}=0.18

. The particle count at that temperature is 4

\mathrm{NO}_{2}

and 3

\mathrm{N}_{2}\mathrm{O}_{4}

. The temperature is then changed so that the new equilibrium constant becomes

K_{\text{new}}=0.050

while the particle counts remain the same at the instant of the change. Which statement correctly predicts the net direction of the reaction immediately after the temperature change? (a) The reaction will shift toward products, producing more

\mathrm{N_{2}O_{4}(g)}

. (b) The mixture is already at equilibrium at the new temperature, so no net change will occur. (c) The reaction will shift toward reactants, producing more

\mathrm{NO_{2}(g)}

. (d) The direction of the shift cannot be predicted without knowing the total pressure of the system.

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