9.5 Hess's Law

Hess’s Law

• In going from a particular set of reactants to a particular set of products, change in enthalpy is the same whether the reaction takes place in one step or a series of steps 

Hess’s Law rules

1) if reaction is reversed, ∆H is negative

2) If the coefficients in a balanced equation are multiplied by an integer, the value of ∆H is multiplied by the same integer 

How to do Hess’s Law

1) start with reactants

2) add more reactants and multiply coefficients to cancel everything out

3) add up

x

x