Constant pressure calorimeter

A constant pressure calorimeter is also known as a coffee cup calorimeter. It is a very simple device; basically it can be made from two styrofoam cups, a stirrer and a thermometer. Placing the two styrofoam cups inside each other (for insulation), a chemical reaction in a liquid medium (typically water) is performed in the inner cup, and the change in temperature recorded. It is called “constant pressure calorimeter” because the system is open to the atmosphere and thus records the temperature change at constant pressure. The temperature change will likely cause the reaction mixture to expand or contract a little, but the volume change is for all practical purposes negligible.

The calorimeter is made of two nested styrofoam cups. The inner cup contains the reaction mixture, a stirrer, and a thermometer. A styrofoam cover is placed over the top of the cup. The stirrer and thermometer poke through the cover so the mixture can be stirred and the temperature can be read. The outer cup provides insulation.

Figure 1: A constant pressure calorimeter, also called a coffee cup calorimeter, can be constructed with two styrofoam coffee cups and a thermometer.

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Calorimetry