The formation of sulfur trioxide from sulfur dioxide and oxygen is represented by

CHEMISTRY · Multi-part · A Level · Chemistry · Thermodynamics · Thermodynamics

Problem

2\,\text{SO}_2(g) + \text{O}_2(g) \leftrightarrow 2\,\text{SO}_3(g)

. The equilibrium constants for the reaction at two temperatures are given below:

Temperature ( $\text{K}$ )	$K$
$700$	$4.2 \times 10^4$
$800$	$6.3 \times 10^2$

Assume

R = 8.314\,\text{J\,mol}^{-1}\,\text{K}^{-1}

. (a) Calculate the standard Gibbs free energy change,

\Delta G^\circ

, for the reaction at

700\,\text{K}

\mathrm{kJ\,mol}^{-1}

. (b) Calculate

\Delta G^\circ

for the reaction at

800\,\text{K}

\mathrm{kJ\,mol}^{-1}

. (c) Using the values obtained in parts (a) and (b), determine the sign of the standard enthalpy change,

\Delta H^\circ

, for the reaction and justify your answer without performing a full Van ’t Hoff analysis. (d) Predict qualitatively whether the equilibrium constant at

900\,\text{K}

will be greater than, equal to, or less than the value at

800\,\text{K}

. Support your prediction with reasoning based on thermodynamic principles.

Related theory

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