The surplus of energy that is released is lost as heat. When carbon burns it reacts with oxygen - this reaction is exothermic. The amount of heat produced depends on the amount of carbon burnt. The enthalpy of reaction is negative when the reaction is exothermic. The opposite is generally true for a reaction which is endothermic.
More energy is required to break existing bonds than is released when new bonds are formed.
The shortfall of energy is absorbed from the surroundings and a cooling effect can be measured. The enthalpy of reaction for an endothermic reaction is positive.