Effect of temperature on equilibrium
I'll try and simplify the answer.



Looking at the image above, imagine the products sitting above the letter D and the reactants sitting below the letter B.  Now, imagine the particles involved in the reaction moving since they have kinetic energy.  It is much easier for the reactants to climb up the top of the hill labeled C then it is for the products to climb up the hill.  Once a reactant climbs the hill and slides down to products it will not be able to go back to reactants by climbing up the hill unless we give them more energy by raising temperature.  Raising temperature allows the products to climb up the hill and go to reactants.  

The forward reaction in the diagram is exothermic and the reverse is endothermic.  So, the exo is favored at low T and the endo at high T.

You can also look at the equation delta G = delta H - Tdelta S.

Make up some numbers for delta H and delta S.  You will see that endo reactions becomes more spontaneous as you raise T and exo reactions become more spontaneous as you lower T regardless of delta S.