SCH4U - Chemistry 12 (2024-25) - A

In this lesson, you will be introduced to the concept of Hess's Law.  Hess's Law can be used to calculate changes in enthalpy for reactions that are too difficult to measure directly.  By applying Hess's Law, we can take known changes in enthalpy from common reactions and combine them in such a way to calculate the net change in enthalpy for an unknown reaction.

Learning Goals:

By the end of this lesson you will:

• • • Be able to define Hess's Law.
    • Understand how to combine multiple chemical reactions to produce a single net reaction.
    • Apply Hess's Law using a table of Standard Enthalpies of Formation to calculate changes in enthalpy.

Success Criteria

I know I have achieved the goals of this lesson when I can define Hess's Law, determine the net reaction by combining multiple steps to end up with the proper reactants and products of the net reaction and can determine the change in enthalpy of a reaction by applying Hess's Law.