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

Given that, enthalpy of combustion of 1 g graphite = 20.7 kJ
Molar enthalpy change for the combustion of graphite, `Delta H =` enthalpy of combustion of 1 g graphite `xx` molar mass
`Delta H = - 207 kJg^(-1) xx 12 g mol^(-1)`
`Delta H = - 2.48 xx 10^(2) kJ mol^(-1)`
Negativve sign in the value of `Delta H` indicates that the reaction is exothermic.