Chapter 6, Problem 91RQ

Write the thermochcmical equations, including values of $\Delta H°$ in kilojoules per mole (from Table 6.2), for the formation of each of the following compounds from their elements, with everything in standard states.

(a) ${\text{HC}}_{\text{2}}{\text{H}}_{\text{3}}{\text{O}}_{\text{2}}\text{(}l\text{), acetic acid}$

(b) ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}\left(l\right)\text{, ethyl alcohol}$

(c) ${\text{CaSO}}_{\text{4}}\cdot {\text{2H}}_{\text{2}}\text{O(}s\text{), gypsum}$

(d) ${\text{Na}}_{\text{2}}{\text{SO}}_{\text{4}}\text{(}s\text{), sodium sulfate}$

compound (from its elements). We can obtain the enthalpy of formation of two moles of water ( $\Delta H°$ for the second equation) simply by multiplying the $\Delta H_{\text{f}}^{\text{°}}$ value for 1 mol of ${\text{H}}_{\text{2}}\text{O}$ by the factor 2 mol ${\text{H}}_{\text{2}}\text{O}\left(l\right)$.

$\frac{-285.9\text{ kJ}}{1{\text{ mol H}}_{\text{2}}\text{O}\left(l\right)}\times 2{\text{ mol H}}_{\text{2}}\text{O}\left(l\right)=-571.8\text{ kJ}$