kaffekoppkalorimeter

The kaffekoppkalorimeter, or coffee cup calorimeter, is a simple constant-pressure calorimeter used to measure the heat change of reactions conducted in aqueous solution. It typically consists of two nested Styrofoam cups, a lid with a hole for a thermometer, and minimal heat exchange with the surroundings. The inner cup holds the reacting solution, while the insulating setup reduces heat loss to the environment, making it suitable for teaching and small-scale experiments.

Principle and calculation: When a reaction occurs in the solution, heat is absorbed by the solution and by the calorimeter. The total heat absorbed is Q = (msol Cs + Ccal) ΔT, where msol is the mass of the solution, Cs is its specific heat capacity (about 4.18 J/g·K for water), ΔT is the temperature change, and Ccal is the calorimeter’s heat capacity. The heat of reaction at constant pressure is qrxn = -Q, and the enthalpy change ΔHrxn ≈ qrxn for reactions performed in solution.

Procedure and calibration: A known amount of solute is dissolved or reacted, the temperature change is recorded, and the calorimeter constant Ccal is determined from a calibration reaction with a known enthalpy change. The approach assumes good thermal contact, complete mixing, and negligible heat loss to the surroundings.

Applications and limitations: The coffee cup calorimeter is widely used in introductory chemistry labs to estimate enthalpy changes of reactions in aqueous solution. Limitations include heat exchange with the environment, dissolution or side reactions, and the need for careful mixing. It is most effective for small temperature changes and dilute solutions, while more precise methods exist for rigorous calorimetry.