Calorimetry

Calorimetry is a technique to determine the amount of heat energy absorbed or released as a process occurs. In order to perform calorimetry:

• The process is performed inside an insulated container.

• The mass of the substance inside the container must be known.

• The specific heat of the substance inside the container must be known.

• The temperature change of the substance inside the container must be known.

Insulated containers are used to reduce the amount of heat that is transferred between the inside and outside of the container. If the process is insulated, any changes in the temperature inside the container is then assumed to be due to the process taking place inside the container.

Performing calorimetry makes several assumptions that introduce error into the measured values.

• The insulated container is assumed to prevent heat transfer. Unfortunately, insulated containers only reduce heat transfer. They do not prevent heat transfer.

• Many processes occur in water-based solutions. This means that the specific heat of the solution can be assumed to be 4.18 J g-1 °C-1. This value is for pure water so the actual specific heat of the solution may be different. To correct for this, the specific heat of the solution should be determined and not assumed.

• The density of the solution is assumed to be 1.0 g cm-3. This allows for the mass of the solution used to be based on the measured volume. The actual mass of the solution may be different than the assumed mass. To correct for this, the mass of the solution should be determined and not assumed.

Measuring energy changes during combustion reactions requires a few modifications of the calorimeter. The primary difference is where the process is occurring. The reaction occurs below a container of water, with the assumption that all of the heat energy during the combustion goes into the water. Even with a carefully insulated calorimeter, a large amount of heat will not be transferred to the water causing the measured temperature change to be less than the theoretical change.