Experiment 1- Chemical Equilibrium

Questions

1. State how and explain why the equilibrium 2X + Y Z will shift if:(a) X is removed

According to Le Chatelier’s principle, when X is removed, the concentration of X becomes lower, it causes the system to counteract the change by shifting the position of equilibrium to the left which has a lower concentration, thus decreasing the yield of Z and increase the amount of X and Y.

(b) Extra Y is addedAccording to Le Chatelier’s principle, when extra Y is added, the concentration of Y increases, it causes the system to counteract the change by shifting the position of equilibrium to the right which has a lower concentration, thus increasing the yield of Z and decrease the amount of X and Y.

(c) Some Z is addedAccording to Le Chatelier’s principle, when some Z is added, the concentration of Z decreases which causes the system to counteract the change by shifting the position of equilibrium to the to the left, therefore increasing the amount of X and Y, hence producing less yield.

2. Define, state or describe(a) The common ion effect

The common ion effect is defined as the suppression of the degree of dissociation of a weak electrolyte containing a common ion. It is also known as the displacement of equilibrium by the addition of more than one element involved in the equilibrium.

(b) Le Chatelier’s principleLe Chatelier’s principle states that if an external change is made in a reaction, the reaction would counteract the change by establishing a new equilibrium. Le Chatelier’s principle is also used to predict how the change in concentration of reactants and products, change in temperature and change in pressure could change the position of equilibrium.

(c) Are there any reactions occurring when a system is at equilibrium?Yes. When a system is at equilibrium, reaction still occurs but the rate of product yield and the rate of reactants formed are the same.

3. Consider the following equilibrium:

2CrO4 2-

(aq) + 2H+(aq) Cr2O7

2- (aq) + H2O(l)

Predict and explain the direction of the position of equilibrium will shift upon:(a) Addition of NaOH

Position of equilibrium will shift to the left. When NaOH is added, the concentration of H+ ions decreased. According to Le Chatelier’s principle, a decrease of concentration of H+ ions would cause the system to counteract the change by shifting the position of equilibrium to the left, therefore increasing the amount of CrO4

2- and produces less yield.

(b) Addition of HClPosition of equilibrium will shift to the right. When HCl is added, the concentration of H+ increases. According to Le Chatelier’s principle, the increase of concentration of H+ ions would cause the system to counteract the change by shifting the position of equilibrium to the right, which has a low concentration, therefore increase the formation of product which is Cr2O7

2- and decrease the amount of CrO4

2-.