Question

Heat of formation of $S{O}_2$ is $-298kJ$. What is the heat of combustion of $4g$ of $S$?

• A. $+37kJ$
• B. $-37.15kJ$
• C. $+298kJ$
• D. $18.6kJ$

Answer 1

The correct option is B $-37.15kJ$

Write the equation for the combustion of $S{O}_2$. The heat of combustion is total heat changes accompanying when one mole of substance undergoes complete combustion in excess of oxygen.

$S+O_2⟶S{O}_2,$

$\Delta H=298kJ$

$\therefore$ Heat of formation of $S{O}_2=$ heat of combustion of $S{O}_2$

Atomic mass of $S=32g$

$\because$ Combustion of $32g$ of $S$ ($=1$ mole of $S$) gives heat $=-298kJ$

$\therefore$ Combustion of $4g$ of $S$ gives heat $=\frac{-298}{32}\times 4$

$=-37.25kJ$

Hence, the correct answer is option $\text{B}$.