We are provided with the amount of energy released when one mole of carbon reacts. We mus first convert the given mass of carbon to moles and then compute the energy released for the given amount.
Moles = mass / atomic mass Moles = 23.5 / 12 Moles = 1.96 moles
One mole releases 394 kJ/mol 1.96 moles will release: 394*1.96 = 772.24
The enthalpy change of the reaction will be -772.24 kJ
