Combustion reactions are exothermic. The heat of reaction for the combustion of butane, C4H10, is 687.8 kcal/mol. What is the heat of combustion for butane in kcal/gram? ______ kcal/gram How much heat will be given off if molar quantities of butane react according to the following equation? 2 C4H10 + 13 O2 8 CO2 + 10 H2O _________ kcal