Question

What generalizations can be made about equilibrium and changes in concentration? Use the simulation below to help you answer the question.After changing the height of the bars in the graph, they re-adjust, but eventually stop. Why?

Answer 1

According to the law of mass action

the equilibrium constant is given by K_c = [AB] / [A][B]

K_c is a constant at given temperature

If the conentration of a reactant is increased, Kc will tend to decrease (because the denominator in the above equation is increased). But Kc is a constant. So in order to maintain the constancy of Kc, the numerator will increse. That is the concentration of AB will increase.In other words more product will be formed (We say the equilibrium is shifted to the right)

If the conentration of a reactant is decreased, Kc will tend to increase (because the denominator in the above equation is decreased). But Kc is a constant. So in order to maintain the constancy of Kc the numerator will decrease. That is the concentration of AB will decrease. In other words less amount product will be formed (We say the equilibrium is shifted to the left)

If the conentration of the product is increased, Kc will tend to increase (because the numerator in the above equation is increased). But Kc is a constant. So in order to maintain the constancy of Kc the denomiator will increse .That is the concentrations of A and B will increase.In other words more reactant will be formed (We say the equilibrium is shifted to the left)

If the conentration of the product is decreased, Kc will tend to decrease (because the numerator in the above equation is decreased). But Kc is a constant. So in order to maintain the constancy of Kc the denomiator will decrease.That is the concentrations of A and B will decrease .This is possible only if more product is formed.So more product will be formed (We say the equilibrium is shifted to the right)

The chemical equilibrium is a dynamic equilibrium. So the two opposing reactions (forward and reverse) never stop. Even at the state of equilibrium, both forward and reverse reaction proceed. But since, the rates of the two opposing reactions are equal at the state of equilibrium, there is apparently no change in the concentration.

After changing the height of the bars in the graph they readjust and eventually stops because the concentrations of the reactants and product are adjusted until the equilibrium is reached and Kc is kept constant. ( It is the graph which stops and not the two opposing reactions)