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

Explanation

Molar enthalpy change of combustion of graphite `=` Enthalpy of combustion of 1 g `xx` Molar mass
`= 20.7 kJ mol^(-1) xx 12 g mol^(-1)`
i.e., `DeltaH = - 2.48 xx 10^(2)kJ mol^(-1)`
Negative value of `DeltaH` shows that the reaction is exothermic .