The reaction shifts forward (to the right), x = 0.78037 M
| H2 | I2 | HI | |
|---|---|---|---|
| Initial | 1 | 1 | 0 |
| Change | −x | −x | +2x |
| Equilibrium | 0.2196 | 0.2196 | 1.561 |
Solved numerically so that [products]^coefficients ÷ [reactants]^coefficients = K exactly — no "x is small" approximation. Concentrations are in mol/L; for gas-phase Kp, enter partial pressures instead.
How it works
The calculator writes each equilibrium concentration as its initial value plus coefficient × x (products) or minus coefficient × x (reactants), then finds the x that makes the reaction quotient equal K. It solves numerically in logarithmic form, which is exact for any K — even when the quadratic formula would be needed, or when the equation is cubic or higher.
It also tells you which way the reaction shifts: forward if the starting Q is less than K, in reverse if Q is greater. Leave pure solids and liquids out of the equation, because they don't appear in K.
Frequently asked questions
- What is an ICE table?
- A table of Initial, Change and Equilibrium concentrations for each species. The changes are linked by the coefficients through a single unknown, x.
- When can I use the "x is small" approximation?
- When K is very small compared with the starting concentrations (roughly, when x is less than 5 % of the initial value). This calculator doesn't need the approximation, so you can check whether it was valid.
- Does this work for Kp?
- Yes — enter partial pressures instead of concentrations and Kp instead of Kc.
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