Ncert Exercises & Solutions

If the combustion of 1g of graphite produces 20.7 kJ of heat, what will be molar enthalpy change? Give the significance of sign also.

Given that, enthalpy of combustion of 1g graphite=20.7 kJ

Molar enthalpy change for the combustion of graphit,

∆ H =

enthalpy of combustion of 1 g graphite

\times

molar mass

∆ H = - 20.7 {kJg}^{- 1} \times 12 g {mol}^{- 1}

∆ H = - 2.48 \times 10^{2} kJ {mol}^{- 1}

Negative sign in the value of

∆ H

indicates that the reaction is exothermic.