Problem

A closed reaction vessel at 400 °C contains a gaseous mixture for the synthesis of hydrogen chloride according to the balanced equation

\mathrm{H_2(g)+Cl_2(g) \rightleftharpoons 2HCl(g)}

The equilibrium constant for the reaction at 400 °C is

K_c = 3.5\times10^{3}

. The instantaneous (not-at-equilibrium) molar concentrations in the vessel are •

[\mathrm{H_2}] = 1.0\times10^{-2}\,\text{M}

•

[\mathrm{Cl_2}] = 1.0\times10^{-2}\,\text{M}

•

[\mathrm{HCl}] = 0.65\,\text{M}

No additional quantitative data are provided beyond the values above. (a) Without performing a detailed numerical calculation, use reasoning based on the definition of

Q_c

to predict whether the reaction mixture will experience a net formation of reactants or products as it approaches equilibrium. Explicitly reference the relative magnitudes of the numerator and denominator of the

Q_c

expression in your explanation. (b) Describe qualitatively how the molar concentrations of

\mathrm{H_2}

\mathrm{Cl_2}

, and

\mathrm{HCl}

will change over time until equilibrium is re-established. Include particulate-level reasoning (that is, which species’ molecules are consumed or generated) to support your answer.

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