The two elementary processes below are studied under identical standard conditions

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

Problem

The two elementary processes below are studied under identical standard conditions. Process X:

\text{C}_{2}\text{H}_{6}(g) \longrightarrow 2\,\text{C}(s,\text{graphite})+3\,\text{H}_{2}(g)

Process Y:

6\,\text{C}(s,\text{graphite})+9\,\text{H}_{2}(g) \longrightarrow 3\,\text{C}_{2}\text{H}_{6}(g)

The magnitude of the standard entropy change for Process X is reported as

\lvert\Delta S^{\circ}_{X}\rvert = 254\,\text{J\,mol}^{-1}\,\text{K}^{-1}

. (a) Without performing any numerical calculation, state the sign (positive or negative) of

\Delta S^{\circ}_{X}

and justify your choice in terms of changes in the amount of gas. (b) Process Y is the reverse of Process X but carried out on a different stoichiometric scale. Describe how the magnitude and sign of

\Delta S^{\circ}_{Y}

are related to

\Delta S^{\circ}_{X}

. Provide a verbal explanation referencing the coefficients in the balanced equations. (c) Explain in a short paragraph why multiplying a balanced chemical equation by a factor other than Unity necessarily changes the numerical value of the associated standard entropy change even though the intensive thermodynamic state variables remain the same.

Related theory

Browse the problem library