How does a coffee cup calorimeter work?

A coffee cup calorimeter works by measuring the heat transfer during a chemical reaction in a liquid solution.

A coffee cup calorimeter is a simple, yet effective tool used in thermodynamic experiments to measure the heat of reaction, or the amount of heat energy transferred during a chemical reaction. It is called a 'coffee cup' calorimeter because it is made from two nested Styrofoam cups, which serve as excellent insulators to prevent heat loss to the surroundings.

The calorimeter contains a thermometer and a stirrer. The thermometer measures the initial temperature of the solution. A chemical reaction is then initiated within the solution, and the thermometer records the change in temperature over the course of the reaction. The stirrer ensures that the solution is well mixed, so that the temperature is uniform throughout.

The heat of the reaction, q, can be calculated using the formula q = mcΔT, where m is the mass of the solution, c is the specific heat capacity of the solution, and ΔT is the change in temperature. The specific heat capacity is a property of the substance being studied, and it represents the amount of heat required to raise the temperature of one gram of the substance by one degree Celsius.

It's important to note that coffee cup calorimeters are constant-pressure calorimeters. This means they measure the change in enthalpy (∆H) of a reaction occurring in solution. The change in enthalpy is equivalent to the heat of reaction at constant pressure.

While coffee cup calorimeters are relatively simple and inexpensive, they are not perfectly insulated, so some heat exchange with the surroundings is inevitable. This can introduce some error into the measurements. However, for many purposes, especially in educational settings, a coffee cup calorimeter provides a good approximation of the heat of reaction.