A thermochemical equation is a balanced equation that takes into account the heat flow of a reaction. The heat flow is commonly presented in kilojoules and appears immediately to the right of the equation.
Obtained from heat of formation tables, this heat flow, or enthalpy change, is represented by the symbol ΔH. Heat of formation tables apply a standard temperature of 25 degrees C in their enthalpy calculations. Since enthalpy is directly proportional to mass, doubling the coefficients of a thermochemical equation also doubles the resulting heat flow. If the heat flow figure is in the negative, it is indicative of a chemical reaction that gives off energy. A positive figure indicates that it absorbs energy.