This document discusses exothermic and endothermic chemical reactions. It defines exothermic reactions as releasing heat and endothermic reactions as absorbing heat from their surroundings. Combustion reactions of hydrocarbons like methane and propane are exothermic, producing carbon dioxide, water vapor, and large amounts of heat. The heat of reaction quantity describes the amount of heat absorbed or released by a chemical reaction. A bomb calorimeter is used to accurately measure the heat of combustion of fuels by completely combusting samples in excess oxygen and measuring the temperature change of the surrounding water.