Measuring a temperature change
Calorimetry is a technique used to measure enthalpy changes in chemical reactions from measured temperature changes.
A calorimeter may be a polystyrene cup, a vacuum flask or a metal can. An insulated polystyrene cup is commonly used for reactions taking place in solution.
A typical solution-calorimetry setup includes:
- a polystyrene cup, with a beaker providing support and additional insulation
- a plastic lid to reduce heat exchange
- a thermometer or temperature probe with its bulb immersed in the reaction mixture
- measured quantities of the reactants
- stirring so that the solution is at a uniform temperature.
Typical procedure
- Rinse the relevant apparatus with the solutions being used and dry the calorimeter cup after washing.
- Measure the required volume of solution and transfer it to the insulated cup.
- Place the thermometer or probe in the solution, stir and record the temperature at regular intervals for a few minutes before the reaction begins.
- Add the second reactant at a known time. If a solid is used, weigh its container before transfer and again afterwards; use the difference to find the mass added.
- Continue stirring and record the temperature at regular intervals for several minutes after addition.
If two solutions are used, determine the initial temperature from measurements of both solutions before they are combined.
Exam Tip: A complete method should identify the insulated cup, thermometer or temperature probe and stirring, and should include temperature readings before and after the reactants are mixed.