Lesson 5: Hess' Law
Curriculum Expectations
Minds-On
Facilitate a class discussion to review what students have learned so far in thermochemistry. Using the example of a natural gas heater for a home, ask students how you would determine how much heat is produced. With the knowledge they have gained in classes up until this point, students should arrive at a thermochemical equation that describes combustion and releases heat. But actually, the process also involves the evaporation of water, which requires energy. This exemplifies the idea that enthalpy is cumulative in a reaction process and that it is a state function.
Pedagogical Approach
- The YouTube video below is an excellent teacher resource that explains Hess' Law. Throughout a note on Hess' Law, describe alternate examples of Hess' law to students, such as the oxidation of carbon to carbon monoxide and carbon dioxide. Facilitate a discussion to identify other examples of Hess' Law
- This interactive activity guides students through problems related to Hess' Law