Calorimetry experiments for determining the enthalpy changes of reactions
2 marks · HardA student carries out a simple calorimetry experiment to measure the enthalpy change of combustion of a fuel. State two specific sources of error or limitations in this type of calorimetry experiment that could cause the measured value to be less exothermic (less negative) than the accepted value.
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Also accept: heat loss to surroundings (air) or container; incomplete combustion of fuel; heat absorbed by apparatus (not measured); evaporation of fuel before/after burning
Common mistakes: incorrectly stating apparatus names; listing general laboratory errors without explanation
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States an appropriate source of error (e.g. heat loss to surroundings, incomplete combustion).
B2 · 1 mark · States a second, different source of error or limitation.
Worked solution
Two specific sources of error which could cause the measured value of enthalpy change to be less exothermic than expected are:
1. Heat is lost to the surroundings (e.g., to the air or to the copper can), so not all energy released by the fuel heats the water.
2. Incomplete combustion of the fuel, which means some of the fuel does not release its full heat energy because it does not burn completely.