Calorimetry experiments for determining the enthalpy changes of reactions
2 marks · EasyA student’s value for the enthalpy change of combustion of methanol is much less exothermic than the accepted value found in data books. Explain two possible sources of error or limitations in the student’s calorimetry experiment.
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Also accept: heat loss from flame to air; not all the energy heats water; use of poor insulator
Common mistakes: Insufficient stirring; Not using a lid; Not mentioning heat loss or incomplete combustion
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Marking points
B1 · 1 mark · Mentions heat loss to surroundings, for example heat escapes from the copper can or water to the air.
B2 · 1 mark · Mentions incomplete combustion of methanol, or not all fuel burnt completely due to lack of oxygen.
Worked solution
Two possible sources of error are: (1) Heat is lost from the copper can or water to the air, so not all heat from combustion is measured; (2) Incomplete combustion of methanol may occur if there is not enough oxygen, so less heat is released.