Some students apply Le Chatelier's Principle incorrectly to the effect of temperature on equilibrium position.

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Another related problem is that endothermic reactions are shown as +X kJ mol^–1. This can be confusing as increasing the temperature favours this reaction.

How should students correctly apply Le Chatelier's Principle to predict the effect of increasing the temperature of the equilibrium mixture?

If the temperature of the mixture is raised the endothermic change will be favoured because this will tend to lower the temperature of the system. 

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How might you explain the effect of temperature on the position of equilibrium?

The explanation of why temperature affects the equilibrium position in the way it does is quite challenging. For many students it may be sufficient for them to find out by experiment how equilibrium reactions respond to temperature changes and so build up a general rule that applies to all equilibrium systems. A qualitative explanation can be given in terms of a difference in activation enthalpy of forward and reverse reactions without going into more mathematical detail.

An energy diagram provides a clear visual representation of the difference in activation enthalpy in forward and back reactions. This can prove useful in explaining the effect of temperature on equilibrium position.

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Some students think that Le Chatelier's Principle provides an explanation of change of equilibrium position rather than being a useful prediction device.

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When might you use Le Chatelier's Principle to describe the effect of temperature change on the position of equilibrium?

Le Chatelier's Principle is a useful predictive device but it is not an explanation. It is best introduced after examples of the effect of changing temperature have been met rather than before this has happened. It then becomes a summary of existing knowledge rather than an introduction to new knowledge.