In this work, we derive a simple dynamic model for a 1.2 kW polymer electrolyte membrane (PEM) fuel cell stack and compare the model results to the operation of a real 1.2 kW cell stack. Our model includes component balances and considerations for water and oxygen and also heat effects due to non-isothermal operation. We first develop a mathematical model that captures the characteristics of a single PEM fuel cell, then generalize this model by adjusting key parameters to approximate the behavior of the entire stack. We choose to model this single cell by two linked continuously stirred tank reactor (CSTR) chambers separated by a proton exchange membrane which allows for charge and mass transfer. The model is coupled to dynamic mass and energy balances that quantify the transport of hydrogen ions, oxygen, water, and heat.