TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > Edexcel GCE Chemistry Specification
Some chemical reactions do not react until all reactants have been used up. This happens when a system is in equilibrium - the amount of products and reactants no longer change. This is not because the reactions have stopped taking place; just the rate of the forward and the backward reactions are equal. Systems like this are said to be in dynamic equilibrium.
In an equilibrium system, an external change may change the position of equilibrium, or how much reactants and products there are. The response of the system will always be to oppose the change:
- An increase in temperature favours the endothermic reaction
- An increase in pressure favours the reaction with fewer moles of gas produced
- An increase in concentration favours the reaction which uses that element/compound
(Edexcel require the example of methane/methane hydrate... :/)
