Calorimetry experiments for determining the enthalpy changes of reactions
4 marks · NormalNeutralisation experiments using polystyrene cups are often used to calculate enthalpy changes of reaction.
Give one reason why a polystyrene cup is used instead of a metal can.
Suggest one way the experiment might underestimate the enthalpy change.
State one possible way to minimise errors from heat lost during the experiment.
Explain how using a lid can help improve the accuracy of a calorimetry result.
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(a) Polystyrene is a good insulator / reduces heat loss.
(b) Heat lost to surroundings / not all heat goes to solution.
(c) Place a lid on the cup / use extra insulation.
(d) A lid helps keep more heat inside the cup, so less energy escapes to the air. This gives a more accurate measurement of the temperature change and enthalpy change.
Common mistakes: giving vague answers like improve experiment without detail
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Marking points
B1 (a) · 1 mark · States that polystyrene is a good insulator or reduces heat loss.
B2 (b) · 1 mark · Suggests heat is lost to the surroundings or not all heat goes to the solution.
B3 (c) · 1 mark · States any reasonable way to minimise heat loss, e.g., add a lid or more insulation.
B4 (d) · 1 mark · Explains that a lid reduces heat loss to air and improves the accuracy of the measured enthalpy change.
Worked solution
(a) A polystyrene cup is a good insulator so it reduces energy loss to the surroundings.
(b) The experiment may underestimate enthalpy change because heat is lost to the air instead of the solution.
(c) A lid can be used to further reduce heat loss.
(d) By minimising heat loss to the surroundings, the measured temperature rise more closely matches the true energy change of the reaction.