Science Common Sense

1728 - What is Hess's law for the additivity of reaction heats?

Hess's Law is a simple rule that helps us calculate the heat energy (or temperature change) of a chemical reaction.

It says that if you have a chemical reaction that takes place in more than one step, you can add up the heats of each step to get the total heat of the whole reaction.

Think of it like a journey. Imagine you're traveling from point A to point C, but with a stop at point B. The total distance you travel is the same whether you go from A to C directly, or if you go from A to B and then from B to C.

In the same way, Hess's Law says that the total heat energy of a chemical reaction is the same, no matter how many steps the reaction takes. You can add up the heat energies of each step to get the total heat energy of the whole reaction.