When a system in equilibrium undergoes a change in temperature due to the addition or removal of heat, it responds in a way that tends to counteract the temperature change. This phenomenon is governed by Le Chatelier's principle, which states that a system at equilibrium will adjust its conditions to minimize the effect of any external disturbance.
In an endothermic reaction, increasing the temperature causes the reaction to shift in the forward direction to absorb the additional heat. By absorbing heat, the reaction consumes thermal energy, resulting in a decrease in the system's temperature. This cooling effect occurs because the reactants absorb the heat to convert into products, reducing the overall kinetic energy of the system.
Essentially, the equilibrium reaction "cools itself down" by using the added heat to drive the endothermic reaction forward, thus counteracting the increase in temperature. The energy absorbed by the reaction is utilized to break existing bonds and form new ones, resulting in the cooling effect.
It's important to note that the cooling effect doesn't mean that the system becomes cooler than its initial temperature before the heat addition. Instead, it prevents the system from getting even hotter by utilizing the added heat to drive the endothermic reaction. The system reaches a new equilibrium at a higher temperature, but not as high as it would have been without the cooling effect.
Le Chatelier's principle ensures that the system adjusts its conditions to maintain equilibrium, counteracting the imposed changes and minimizing their effects.