Le Châtelier's principle states that when there is an dynamic equilibrium, and this equilibrium is disturbed by an external factor, the equilibrium will be shifted in the direction that can cancel the effect of the external factor to reattain the equilibrium.
For endothermic reaction, it can be represented as:
<em>Reactants + heat ↔ Products.</em>
As the temperature cooled, it is like that decreasing the concentration of reactants side, that shifts the reaction towards the lift side (reactants side) to attain the equilibrium again.
<em>So, the reaction is an endothermic reaction.</em>
