What is the difference between a forward and a reverse reaction? I am studying Lechatelier's principal and it states that with an increase in temperature it favors a reverse reaction and when the temperature decreases it favors a forward reaction. What does this mean exactly?
Consider the reaction of
A + B ==> C + D
From left to right is the forward reaction. From right to left is the reverse reaction.
So when A and B are producing C and D we are talking forward reaction. When C and D are reacting to produce A and B we are talking reverse reaction.
The difference between a forward and a reverse reaction lies in the direction in which the reaction proceeds. In a forward reaction, reactants combine to form products, while in a reverse reaction, products react to produce the original reactants.
Le Chatelier's principle states that when a system at equilibrium is subjected to an external stress or change, the system will readjust in a way that minimizes the effect of the stress. One of the factors that can affect a reaction's equilibrium is temperature.
If we consider an exothermic reaction (a reaction that releases heat), increasing the temperature would be considered as an external stress. According to Le Chatelier's principle, the system will respond by trying to counteract the increase in temperature. In this case, to reduce the temperature, the equilibrium will shift in the endothermic direction, favoring the reverse reaction. This means that the equilibrium will shift towards the side with more reactants and fewer products.
On the other hand, if the temperature decreases, it can be considered as a decrease in external stress. The system will respond by attempting to increase the temperature. In an exothermic reaction, this corresponds to favoring the forward reaction, which releases heat. Therefore, the equilibrium will shift towards the side with more products and fewer reactants.
It's important to note that these temperature effects apply specifically to exothermic reactions. For endothermic reactions (reactions that absorb heat), the principle's predictions are reversed; an increase in temperature favors the forward reaction, and a decrease in temperature favors the reverse reaction.