How much heat is released when 75 g of octane is burned completely if the enthalpy of combustion is - 5,500 kJ/mol C8H18

Enthalpy change is the total heat that is absorbed or evolved in a certain reaction that is being carried in a constant pressure system. It can be calculated by the product of the specific heat of the substance and the difference of the final temperature and the initial temperature. For this case, the enthalpy of combustion is given, so we simply multiply the amount of octane present to the enthalpy given to determine the total heat that is released.

Heat = 75 g (1 mol / 114.23 g) ( - 5500 kJ / mol) = - 3611.14 kJ

The negative sign in the calculated value represents that this heat is being released in the process.