Le Chatelier Shift Calculator
This Le Chatelier shift calculator predicts which way a chemical equilibrium will move by comparing the reaction quotient Q with the equilibrium constant K. For the simple reaction A plus B forming C, the reaction quotient is the product concentration divided by the product of the reactant concentrations, evaluated at the current, not necessarily equilibrium, state. Le Chatelier's principle, expressed quantitatively through the Q versus K comparison used in physical chemistry references such as those from the US National Institute of Standards and Technology, says the system responds to relieve the imbalance. If Q is less than K there is too little product, so the reaction proceeds forward to the right; if Q is greater than K there is too much product, so it runs in reverse to the left; and if Q equals K the system already sits at equilibrium. Enter the current concentrations of A, B and C and the equilibrium constant K, and the calculator returns Q, compares it with K, and states the shift direction. Every figure is computed deterministically from the reaction quotient formula shown in full below, with a worked example that reconciles exactly to the calculator so you can follow each step yourself.
Comparing Q with K gives the direction: for A + B forming C with [A] = [B] = 1.00 and [C] = 2.00, Q = 2.00, and against K = 4.00 the reaction shifts forward (to the right) because Q is less than K.
Reaction quotient and shift rule
for A + B forming C: Q = [C] / ( [A] x [B] )
Q less than K: shifts forward (to the right)
Q greater than K: shifts reverse (to the left)
Q equals K: already at equilibrium
The reaction quotient has the same algebraic form as the equilibrium constant but uses the current concentrations. Comparing Q with K tells you whether the products are under-represented or over-represented relative to equilibrium, and the system shifts in whichever direction restores the balance.
Worked example
Predict the shift for A + B forming C with [A] = 1.00, [B] = 1.00, [C] = 2.00 and K = 4.00.
- Q = [C] / ([A] x [B]) = 2.00 / (1.00 x 1.00) = 2.00
- compare: Q = 2.00 versus K = 4.00
- Q is less than K, so there is too little product
- the equilibrium shifts forward, to the right, making more product
The reaction quotient is 2.00, less than K of 4.00, so the equilibrium shifts forward to the right. These are the calculator's default inputs, so the result above matches the widget exactly.
Direction of shift by Q versus K
The comparison of Q with K fully determines the direction of the response.
| Condition | Meaning | Shift |
|---|---|---|
| Q less than K | Too little product | Forward (right) |
| Q equals K | Balanced | No shift |
| Q greater than K | Too much product | Reverse (left) |
Chemical equilibrium and thermodynamics reference: US National Institute of Standards and Technology (NIST).
Le Chatelier Shift Calculator: frequently asked questions
What is the reaction quotient Q?
Q has the same form as the equilibrium constant K but uses the concentrations present at any chosen moment, not just at equilibrium. For A plus B forming C it is the product concentration over the product of the reactant concentrations. Comparing Q to K shows whether a reaction mixture is at equilibrium and, if not, which way it must move to reach it.
How does Q versus K predict the shift?
If Q is smaller than K the mixture has less product than equilibrium demands, so the forward reaction is favored and the system shifts right. If Q is larger than K it has excess product, so the reverse reaction is favored and it shifts left. When Q equals K the forward and reverse rates are balanced and no net shift occurs.
Does this handle reactions with coefficients?
This tool uses the simple stoichiometry A plus B forming C, where every species has a coefficient of one. For reactions with other coefficients you raise each concentration to its stoichiometric power before taking the ratio. The Q versus K logic for predicting the direction is identical once Q is computed correctly.
What about changes in pressure or temperature?
Le Chatelier's principle also covers pressure changes for gas reactions and temperature changes, which actually shift the value of K itself. This calculator addresses concentration-driven shifts at a fixed temperature, the most common classroom case, by comparing the concentration-based Q with a given K.
Can K be less than 1?
Yes. A small K means the equilibrium lies toward the reactants, so only a little product forms. The Q versus K comparison still works exactly the same way: you compute Q from the current concentrations and compare it with whatever value K takes, large or small.
Official sources
- Chemical equilibrium and reference data: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.