How do perturbations to a system affect the equilibrium position of a reaction?

If a perturbation is applied to a system in dynamic equilbirium, the position of equilbirium will shift to favour the reaction which minimises the effect of the perturbation. If the forward reaction is exothermic, and the backwards reaction is endothermic, and the system is heated, the equilibrium position will shift to favour the endothermic reaction, minimising the effect heating. The same effects are seen with pressure and concentration. This is Le Chatelier's Principle.