Question

Internal energy change for combustion of oxalic acid ($H_2{C}_2{O}_4$) is $-245.7kJ/mol$. The enthalpy of the combustion of oxalic acid at ${27}^o$ C is:

• A. $-341.95$ kJ/mol
• B. $-241.95$ kJ/mol
• C. $-182.86kJ/mol$
• D. $-210.68kJ/mol$

Answer 1

The correct option is B $-241.95$ kJ/mol

$H_2{C}_2{O}_4\left(l\right)+\frac{1}{2}{O}_2\left(g\right)\to H_{2}O\left(l\right)+2C{O}_2\left(g\right)$
$\Delta n_g$ = difference in moles of gaseous products and reactants = $2-\frac{1}{2}$ = $\frac{3}{2}$
$\Delta H=\Delta U+n_{g}RT$ = $-245.7+\frac{\frac{3}{2}\times 8.314\times 300}{1000}$ = $-241.95$ kJ/mol