Question

Calculate the heat of formation of methane, given that
heat of formation of water $=-286kJ{mol}^{-1}$
heat of combustion of methane $=-890kJ{mol}^{-1}$
heat of combustion of carbon $=-393.5kJ{mol}^{-1}$

• A. $75.5kJ{mol}^{-1}$
• B. $-75.5kJ{mol}^{-1}$
• C. $-55.5kJ{mol}^{-1}$
• D. $55.5kJ{mol}^{-1}$

Answer 1

The correct option is B $-75.5kJ{mol}^{-1}$

Heat of formation of methane = 2$\times$ heat of formation of water + heat of combustion of carbon - heat of combustion of methane

Heat of formation of methane = $2\ast (-286)+(-393.5)-(-890)$ =$-75.5KJmo{l}^{-1}$