Increase in Yield of products in an exothermic reaction Given an exothermic reaction $\ce{N2 + 3H2 -&gt; 2NH3}$ (which was initially in equilibrium). The temperature is then increasing with time. I am supposed to predict the yield of ammonia with time. 

According to an exothermic reaction, the equilibrium constant K is supposed to decrease with increase in temperature. But it is found that the yield increases initially before decreasing continuously as expected. What causes the initial increase in the yield? 

I suppose that the heat overcoming the activation energy could provide an explanation, but is there any other concept which is not fully reliant on the kinetics of the reaction?
Look, you say: "which was initially in equilibrium". Then the temperature are stable. In the reaction you have four mols in the reactants and 2 mols in the products. When you increase the temperature the system pressure increase too.

So to increase the stability the system "walk" for the reactants, because this decrease the pressure (2 mols in products and 4 mols in reactants).

If you remember the gas ideal law, the pressure is directly proportional to the mol numbers. So this is the reason because the temperature favor the products.