Two animated slides explain the decomposition reactions that occurs within a catalytic converter. An enthalpy diagram is displayed. Hess's Law is demonstrated. Finally, the analogy of football is used to explain Hess's Law. This clever presentation can be used to explain the concept of enthalpy. After showing it, have your pupils practice calculating enthalpy with a worksheet. Note: The links to worksheets on the final few slides do not work; you will need to find or create your own.