A thermochemical equation is the chemical equation for a reaction including phase labels, with the enthalpy of reaction shown immediately after the equation.  In a thermochemical equation the coefficients represent moles and can therefore be fractional.  The following is an example

H₂(g) + 1/2 O₂(g) ==> H₂O(g) H = -286 kJ

In working with thermochemical equations you will find the following rules helpful.

• When a thermochemical equation is multiplied by a factor, the value of  H for the new equation is obtained by multiplying the value of  H by the same factor.
• When a chemical equation is reversed, the sign of  H is reversed.
• If two thermochemical equations can be added to obtain a third equation, the enthalpy of the third equation will be the sum of the enthalpies of the first two reactions.