A clear visual guide to measuring an enthalpy change using a coffee-cup calorimeter, combining practical technique, a complete worked calculation and evaluation of the experimental method.

The experiment uses the exothermic displacement reaction between zinc and copper(II) ions:

Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)

Students are taken through the experiment step by step, from adding zinc powder to copper(II) sulfate solution and measuring the temperature rise, through to calculating an experimental enthalpy change of approximately −130 kJ mol⁻¹.

The resource includes:

Setting up and using a polystyrene coffee-cup calorimeter.
Measuring the initial and maximum temperatures and calculating ΔT.
Calculating the heat gained by the solution using Q = mcΔT.
Calculating the moles of both reactants and identifying the limiting reagent.
Calculating the enthalpy change using ΔH = −Q/n.
Explaining why a positive temperature rise gives a positive value of Q for the solution, but a negative ΔH for the exothermic reaction.
Comparison of the experimental result with the expected value of approximately −218 kJ mol⁻¹.
Explanation of why experimental calorimetry commonly produces a value that is less exothermic than the theoretical value, particularly because of heat losses.

Two important assumptions made in this type of calculation are highlighted:

1. The specific heat capacity of the solution is assumed to be 4.18 J g⁻¹ K⁻¹ — the same as water.

2. The density of the solution is assumed to be 1.00 g cm⁻³ — so 25.0 cm³ of solution is treated as having a mass of 25.0 g.

The resource also considers how the experiment can be improved using nested polystyrene cups, a tight-fitting lid, continuous stirring, regular temperature measurements and temperature-time extrapolation.

Suitable for GCSE, IGCSE and A-level Chemistry, particularly for teaching energetics, calorimetry, enthalpy calculations, limiting reagents, experimental uncertainty and evaluation of practical procedures.

The accompanying animated GIF presents the experiment, calculations, assumptions, explanations and improvements as a sequential classroom demonstration, making it useful for teaching, revision or independent study.