Chemical equilibrium

Forward and reverse reactions Not all chemical reactions occur in one direction. They can go “forward” – to the right. They can go in “reverse” – to the left. Both the forward and reverse reactions have a reaction rate. Chemical equilibrium is reached when the rates of the forward and reverse reactions are equal.

Le Chatelier’s Principle We can disrupt a reactions equilibrium by changing parts of the reaction or the conditions of the reaction. (change temperature, add reactants, add products, etc.) When we do this, the reaction has to make up for the difference, so it “shifts” the equilibrium to make up for the change. If it shifts right, we say that it favors the products or that it favors the forward reaction. If it shifts left, we say that it favors the reactants or that it favors the reverse reaction.

Effect of changing concentration A + B  C + D If we increase the concentration of either A or B, the reaction will shift to the opposite side. In this case the equilibirum will shift to the right in favor of the products. Reason: The reaction needs to “use up” A and B and it does this by making more C and D. EX: Which way will the equilibirum shift if we add more C? More D? EX: Which way will the EQ shift if we remove A? Remove C?