Chapter 18, Problem 127RQ

The enthalpy of combustion $\Delta H_{\text{combustion}}^o$, of oxalic acid, ${\text{H}}_{\text{2}}{\text{C}}_{\text{2}}{\text{O}}_{\text{4}}\left(s\right)\text{, is -246}{\text{.05 kJ mol}}^{\text{-1}}$. Consider the following data:

Substance	$\Delta H_{\text{f}}^{\text{o}} {\text{J mol}}^{\text{-1}}$ 1	$S{\text{°(J mol-}}^{\text{1}}{\text{K}}^{\text{-1}}\text{)}$
CM	0	5.69
${\text{CO}}_{\text{2}}\left(g\right)$	-393.5	213.6
${\text{H}}_{\text{2}}(g)$	0	130.6
${\text{H}}_{\text{2}}\text{O}\left(l\right)$	-285.8	69.96
${\text{O}}_{\text{2}}\left(g\right)$	0	205.0
${\text{H}}_{\text{2}}{\text{C}}_{\text{2}}{\text{O}}_{\text{4}}\left(s\right)$	?	120.1

(a) Write the balanced thermochemical equation that describes the combustion of one mole of oxalic acid.

(b) Write the balanced thermochemical equation that describes the formation of one mole of oxalic acid.

(c) Use the information in the table above and the equations in parts (a) and (b) to calculate $\Delta H_{\text{f}}^{\text{o}}$ for oxalic acid.

(d) Calculate $\Delta S_{\text{f}}^{\text{o}}$ for oxalic acid and $\Delta S°$ for the combustion of one mole of oxalic acid.

(e) Calculate $\Delta G_{\text{f}}^{\text{o}}$ for oxalic acid and $\Delta G°$ for the combustion of one mole of oxalic acid.