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Lesson: Chapter 8 — Heat changes in chemical reactions

Measuring a heat of reaction 1 of 3

The polystyrene cup

Activity 8.3 measures the heat change in a reaction: sodium hydroxide (NaOH) with hydrochloric acid (HCl).

Activity 8.3

You will need: 50 cm3 of 2 mol dm-3 sodium hydroxide solution, 50 cm3 of 2 mol dm-3 hydrochloric acid, two 100 cm3 beakers, a 0–100 °C thermometer, a polystyrene (rigifoam) cup, a glass rod

  1. Measure 50 cm3 of each solution into a separate beaker with a measuring cylinder.
  2. Record the starting temperature of each. Wash the thermometer after the base and before the acid.
  3. Pour both into the polystyrene cup, stir with the glass rod, and record the highest temperature reached.

Figure to be added

Figure 8.4 — the apparatus: a polystyrene cup holding the mixture, closed with a lid, with a thermometer and a glass rod through the lid.

Keeping the heat in

Some heat is always lost to the surroundings and taken up by the container, and it is not counted — an error. The polystyrene cup insulates the mixture to keep that small, and stirring keeps the temperature the same all through the mixture.

HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)