ICE table calculator (equilibrium concentrations)
Enter the equilibrium constant, the coefficients of up to two reactants and two products and their initial concentrations. The calculator solves the ICE table — Initial, Change, Equilibrium — exactly, so it works for weak acids, gas reactions and solubility products alike, and tells you which way the reaction moved.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter K for the reaction as written.
- Enter the coefficient of each species and its initial concentration. Use 0 for a species that is not there (a second reactant, a solid, water).
- Read x, the equilibrium concentration of every species and the direction of the shift.
How it works
For aA + bB ⇌ cC + dD:
|
A |
B |
C |
D |
| Initial |
A₀ |
B₀ |
C₀ |
D₀ |
| Change |
−a·x |
−b·x |
+c·x |
+d·x |
| Equilibrium |
A₀ − a·x |
B₀ − b·x |
C₀ + c·x |
D₀ + d·x |
The equilibrium row must satisfy K = [C]^c·[D]^d ÷ ([A]^a·[B]^b). In logarithms, c·ln[C] + d·ln[D] − a·ln[A] − b·ln[B] − ln K rises steadily with x, so there is exactly one x between “a reactant runs out” and “a product runs out”. The calculator finds it by bisection to full machine precision.
Worked example
Acetic acid, HA ⇌ H⁺ + A⁻, Ka = 1.8 × 10⁻⁵, [HA]₀ = 0.1 M, no ions at the start.
x² ÷ (0.1 − x) = 1.8 × 10⁻⁵ → x² + 1.8 × 10⁻⁵·x − 1.8 × 10⁻⁶ = 0 → x = 0.00133267 M.
At equilibrium [H⁺] = [A⁻] = 0.00133267 M and [HA] = 0.0986673 M; 1.333 % of the acid has dissociated.
Hydrogen iodide: H₂ + I₂ ⇌ 2 HI, K = 64, 1 M H₂ and I₂. (2x)² ÷ (1 − x)² = 64 gives x = 0.8: [H₂] = [I₂] = 0.2 M, [HI] = 1.6 M.
Tips
- Write K for the equation you entered. Doubling all coefficients squares K.
- Concentrations, not moles. Divide moles by the volume first.
- Very large or very small K. The calculator still works, but the tiny remaining concentration of a nearly used-up species is only as precise as the inputs.
Frequently asked questions
What is an ICE table?
A three-row table of Initial concentrations, the Change (−a·x for reactants, +c·x for products) and Equilibrium concentrations. Putting the equilibrium row into the K expression gives one equation in x; solving it gives every concentration.
Does the calculator use the 5 % approximation?
No. It solves the equation exactly by bisection, so it also works when x is not small compared with the initial concentration. For acetic acid (Ka = 1.8 × 10⁻⁵, 0.1 M) the exact x is 0.00133267 M; the shortcut √(Ka × C) gives 0.00134164 M.
How do I enter a solid, a liquid or water?
Leave it out: pure solids and liquids do not appear in K. Set its coefficient to 0. For AgCl(s) ⇌ Ag⁺ + Cl⁻, give A the coefficient 0 and both products 1 — then K is the solubility product.
What if the reaction runs backwards?
When the initial Q is greater than K, x comes out negative: products turn back into reactants. The direction row says which way the reaction moved.
Can I use pressures and Kp?
Yes, as long as all quantities are in the same units: enter partial pressures instead of concentrations and Kp instead of Kc. The mol/L label is then just a placeholder for your unit.