Question

The heat of combustion of carbon to $C{O}_2$ is $-393.5\text{kJ/mol.}$ The heat released upon formation of $35.2\text{g}$ of $C{O}_2$ from carbon and oxygen gas is:

• A. $-630\text{kJ}$
• B. $-3.15\text{kJ}$
• C. $-315\text{kJ}$
• D. $+315\text{kJ}$

Answer 1

The correct option is C $-315\text{kJ}$

Formation of $C{O}_2$ from carbon and dioxygen gas can be represented as
$C\left(s\right)+O_{2\left(g\right)}\to C{O}_{2\left(g\right)};{\Delta }_{f}H=-393.5{\text{kJ mol}}^{-1}$
(1 mole = 44 g)
Heat released on formation of $44\text{g}C{O}_2$
$=-393.5{\text{kJ mol}}^{-1}$
$\frac{=-393.5{\text{kJ mol}}^{-1}}{44\text{g}}\times 35.2\text{g}$
$\approx -315\text{kJ}$