The energetics module is the first of two modules in thermodynamics and is studied as part of the AS course or first year of A level.
Students have met the idea of enthalpy change at GCSE in the context of energy changes associated with chemical reactions and will be familiar with the concept of exothermic and endothermic reactions. Some students may not have called these changes enthalpy changes, but should be familar with constructing anergy level diagrams and using bond energies to calculate an enthalpy change for a reaction from GCSE.
At A level, enthalpy change needs to be rigorously defined and students need to be able to represent named enthalpy changes with equations showing the correct stoichiometry and state symbols. They must be able to define correctly standard enthalpy of formation and standard enthalpy of combustion, and use these, along with Hess' law, to calculate standard enthalpies of reaction.
Hess' law and Hess cycles are of fundamental importance since, once established, they are used in order to extend thermodynamics in the second year of the A level, for example when calculating enthalpies of solution. Born Haber cycles are more complex Hess cycles.
First year thermodynamics also requires students to understand and be able to carry out experiments to measure the enthalpy change associated with a reaction. This includes measuring enthalpy changes associated with combustion reactions and also a wider range of reactions such as neutralisation and displacement reactions. Both of these require an understanding and application of the principles of calorimetry.
Students may be asked to suggest sources of error in experimental measurement of enthalpy changes in order to account for discrepancies and, must take account the direction of the error in their suggestions.
This first encounter with thermodynamics lays the foundation for much of what follows in the second year of A level and so it is well worth taking the time to ensure that students are comfortable with the ideas met before moving on.
Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or other recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.’