How does temperature affect equilibrium, according to Le Chatelier's principle??
In a simple equilibrium we have either $$\ce{A + heat &lt;=&gt; B}$$ where the forward reaction is endothermic and the back reaction exothermic, or $$\ce{A &lt;=&gt; B + heat}$$ where the forward reaction is exothermic and the back reaction endothermic.  So in a simple equilibrium, the reaction in one direction will be exothermic and the reaction in the other direction will be endothermic. 

When the temperature of an equilibrium is increased, the rate of both the forward and back reaction is increased.   However the rate of the endothermic reaction (the reaction that absorbs the added energy) is increased more.  So in the first reaction shown above, adding heat will shift the reaction to the right; in the second reaction heat will push it to the left.  

The reason behind this behavior is that both the forward and back reaction can be described by the Arrhenius equation $$\ce{rate=Ae^{-E_{act}/RT}}$$  and the rate with the larger activation energy (the endothermic reaction) will always be more sensitive to changes in temperature. Therefor, the endothermic reaction will increase faster with increasing temperature than the exothermic reaction will.  Put some numbers into the equation and convince yourself.