Question

Select all of the correct statements about reaction quotients and equilibrium constants from the choices below.

A reaction quotient equals the equilibrium constant at equilibrium.



As a reaction progresses forward toward equilibrium K rises until it reaches Q.



K is the lowest value that Q can have.



As a reaction progresses forward toward equilibrium Q drops.



As a reaction progresses forward toward equilibrium K is the highest value Q attains.



As a reaction progresses backward toward equilibrium K drops until it reaches Q.

Answer 1

The correct answers are-

1. A reaction quotient equals the equilibrium constant at equilibrium.
2. As a reaction progresses forward toward equilibrium Q drops.
3. As a reaction progresses forward toward equilibrium K is the highest value Q attains.
4. As a reaction progresses backward toward equilibrium K drops until it reaches Q.

Explanation-

If a reaction is of the form aA + bB ⇌ cC + dD

Then the reaction quotient (Q) = [C]^{c *} [D]^d / [A]^a* [B]^b   

where  [C], [D], [A], [B] are the concentrations of the reactants and products at any time and condition

And the Equilibrium constant (Kc) = [C]^{c *} [D]^d / [A]^a* [B]^b

where  [C], [D], [A], [B] are the concentrations of the reactants and products only at equilibrium

Now Q can be either =, or > or < Kc

Now the relationship between Q and Kc is-

• When Q = Kc, the system is at equilibrium and there is no shift to either the left or the right.
• When Q < Kc, that means there are more reactants than products. Thus some of the reactants will try to become products to re-establish the equilibrium. Hence the reaction to shift to the right. At this situation, As a reaction progresses forward toward equilibrium K is the highest value Q attains.
• When Q > Kc, that means there are more products than reactants. Thus some of the products will try to become reactants to re-establish the equilibrium. Hence the reaction to shift to the left. At this situation, As a reaction progresses backward toward equilibrium K drops until it reaches Q.