It was first put forward in 1840 by the Swiss-born Russian
chemist Germain Henri Hess (1802-50).
can be converted into products by a series of reactions,
the sum of the heats of these reactions is equal to
the heat of reaction for direct conversation from
reactants to products.
The law can be used to obtain
thermodynamic data that cannot be measured directly.
Sometimes called the law of constant heat summation
and is a consequence of the law of conservation of