Determine the $\Delta {S^\Theta }$ for the combustion of methanol.

$${\text{C}}{{\text{H}}_3}{\text{OH(l)}} + {\text{1}}\frac{1}{2}{{\text{O}}_2}{\text{(g)}} \to {\text{C}}{{\text{O}}_2}{\text{(g)}} + {\text{2}}{{\text{H}}_2}{\text{O(g)}}$$

Using the enthalpy of combustion for methanol from Table 12 of the Data Booklet and the $\Delta {S^\Theta }$ determined in part (d), calculate the standard free energy change for the combustion of methanol.

Explain whether changing the temperature will alter the spontaneity of the reaction.

$\Delta {S^\Theta }\left( { = \sum {S_{{\text{products}}}^\Theta }  - \sum {S_{{\text{reactants}}}^\Theta } } \right) = 2 \times 189 + 214 - (240 + 1.5 \times 205)$;

$= 44.5{\text{ J}}\,{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}/0.0445{\text{ kJ}}\,{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}$

Award [2] for correct final answer.

Do not award M2 if M1 incorrect.

temperature of 298 K;

$\Delta G_{\text{c}}^\Theta  = {\text{(}}\Delta H_{\text{c}}^\Theta  - T\Delta S_{\text{c}}^\Theta  = ) - 726 - 298 \times 44.5 \times {10^{ - 3}}{\text{ (kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}{\text{)}}/$

$=  - 726\,000 - 298 \times 44.5{\text{ (J}}\,{\text{mo}}{{\text{l}}^{ - 1}}{\text{)}}$;

$=  - 739{\text{ kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}/ - 7.39 \times {10^5}{\text{ J}}\,{\text{mo}}{{\text{l}}^{ - 1}}$;

Award [3] for correct final answer.

$\Delta G_{\text{c}}^\Theta$ is always negative and temperature won’t alter spontaneity of reaction;

(d) caused difficulties for candidates with the multiplication factor for the oxygen and the correct units were frequently omitted which caused problems then subsequently in part (e).

In (e), problems of units were widespread.

(f) usually was well done by the better candidates. One G2 comment also stated that it would have been better if the experimental value would have been closer to the expected value.