Learners grasp that solids are more ordered than gases and the associated entropy change can then be calculated from standard values. The negative values can cause confusion drawing a cycle to scale (see Learner Resource 1) can help learners visualise the cycle before they start calculating it.Įntropy can be easily introduced with some high entropy reactions, for example the reaction of a carbonate and acid. A good method is to include a competitive edge: have pairs write down your choice of equation and element and score points by spotting each other’s mistakes.īorn–Haber cycles contain endothermic reactions like atomisation and exothermic ones like electron affinity. This can be a very dry lesson if just written down and discussed. These are: formation, atomisation, 1 st and 2 nd ionisation, electron affinities and lattice enthalpy.
To explain and build Born–Haber cycles you must first have a clear understanding of each of the individual standard reactions and how to define them. However, the ideas behind entropy can be difficult to visualise and explain and there are many pitfalls which catch out even the brightest of learners.
This can lead to a large variety of errors within questions and makes it a very polarising topic.Įntropy and free energy, when boiled down, are fairly straightforward calculations and questions can be attempted with little prior knowledge.
The individual reactions involved – such as atomisation, ionisation and electron affinity – can be hard to visualise and their details easy to mix up and forget. Lattice Enthalpy builds on the concepts learned in Hess cycles and relies heavily on mathematical understanding. This guide focuses on two key areas of A level Chemistry: Lattice Enthalpy and Entropy.