A coffee cup calorimeter is a simple device used to measure the heat transfer during chemical reactions or physical changes. It typically consists of two nested Styrofoam cups, which provide insulation, and a thermometer to monitor temperature changes. The reaction occurs in a liquid, usually water, placed inside the cups. When a substance is added to the water, the calorimeter measures the temperature change, allowing scientists to calculate the heat absorbed or released. This method is commonly used in chemistry experiments to study reactions, such as those involving exothermic or endothermic processes, and to determine specific heat capacities of materials.