Reaction Quotient Calculator
Compare Q to K and see which way a reaction runs.
Work out Reaction Quotient. Compare Q to K and see which way a reaction runs. Shows the working, not just the answer.
Same expression as K, but with whatever concentrations you have right now.
Which way the reaction goes
forward, towards products
Q/K = 0.5
Q and K use the same expression; the difference is only when you evaluate it. Q is now, K is at equilibrium. If Q is below K there is too little product, so the reaction runs forward. Above K there is too much, so it runs back. This is also the sign of ΔG: ΔG = RT ln(Q/K), so Q < K makes ΔG negative and the forward direction spontaneous.
How the Reaction Quotient Calculator works
Enter the reaction quotient and the equilibrium constant and this says which direction the reaction will move and by how far it is out of equilibrium. Q and K use the same expression — the only difference is that Q is evaluated at the current concentrations rather than at equilibrium.
Also known as: q vs k calculator · which direction will the reaction shift · reaction quotient formula · q and k equilibrium calculator
Frequently asked questions
What is the difference between Q and K?
None, in the expression. Q uses whatever concentrations exist right now; K uses equilibrium concentrations. Comparing them tells you which way the system must move to reach equilibrium.
Which way does a reaction shift when Q is less than K?
Forwards, towards products, because there is not yet enough product for the ratio to reach K. When Q exceeds K the reaction runs backwards.
How does Q relate to Gibbs free energy?
ΔG = RT ln(Q/K). Q below K makes ln(Q/K) negative, so ΔG is negative and the forward reaction is spontaneous. At Q = K, ΔG is zero and the system is at equilibrium.
Do solids and liquids go in the Q expression?
No. Pure solids and pure liquids have constant activity and are omitted, in Q exactly as they are in K.
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