When to use Q versus K [ENDORSED]

[Nicole 1F]

When do you use the equation ΔG= ∆G°+ RTlnQ versus ΔG= ∆G°+ RTlnK?

[joycelee1A]

I think you use Q when the system is not in equilibrium.

[Sabrina Fardeheb 2B]

^ Yes, when the Gibb's free energy of the reactants is not equal to the Gibb's free energy of the products, you would use Q because it is not at equilibrium.

You would use K when the reaction is at equilibrium because it is a standard energy change of a reaction.

[Shreya Ramineni 2L]

Q is the reaction quotient while K is the equilibrium constant. You use K at equilibrium or when delta G is equal to 0. You use Q when delta G is not equal to 0.

[Ashley Garcia 2L]

Q is the reaction quotient and expresses the relative ratio of products to reactants at a given instant. Whereas, K is the equilibrium constant and expresses the ratio of products to reactants at equilibrium (when delta G=0).

Use ΔG= ∆G°+ RTlnQ when the system is not at equilibrium.
Use ΔG= ∆G°+ RTlnK when the system is at equilibrium.

[snehabhargava]

You use Q when the reaction is not at equilibrium and use K when the reaction is at equilibrium.

[Audrey Goodman 1F]

K is the ratio of concentration of products to concentration of reactants when the reaction is at equilibrium. Q is the ratio when the reaction is not at equilibrium. Therefore, you would use K when at equilibrium, and Q when not at equilibrium.