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Chemistry

Equilibrium Constant K

K = [products]/[reactants]. Free online Equilibrium Constant K. Calculate equilibrium constant k online — fast, accurate, mobile-friendly, no signup needed.

K
5

Derivation

  1. ├── 01Givenprod = 0.5, rxt = 0.1
  2. ├── 02Formulae.prod / e.rxt
  3. ├── 03Substitutee.0.5 / e.0.1
  4. └── 04Compute K5
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§01What is

Understanding the Equilibrium Constant K

The Equilibrium Constant K computes K from 2 inputs: [products], [reactants]. K = [products]/[reactants].

Chemistry turns grams and moles into reactions. Getting the stoichiometry, dilutions, or concentrations right is the difference between a lab result you can trust and one you can’t reproduce. The Equilibrium Constant K sits in that toolkit — it K = [products]/[reactants]. Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

e.prod / e.rxt

Where

prod
[Products]
rxt
[Reactants]
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: [Products] = 0.5, [Reactants] = 0.1.

  1. 01Start by noting the input — [Products]: 0.5.
  2. 02Start by noting the input — [Reactants]: 0.1.
  3. 03Substitute these values into the formula: e.prod / e.rxt
  4. 04Compute K: the calculator returns 5.
  5. 05Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Equilibrium Constant K Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

[Products] halved

prod = 0.25 (from 0.5)

Keep every other input at its default and halve the [products]. See how k responds.

  1. 01New [Products]: 0.25
  2. 02Baseline K: 5
  3. 03New K: 2.5
  4. 04K decreases by 50% → use this sensitivity to plan for real-world variation.
02 · PATTERN

[Products] doubled

prod = 1 (from 0.5)

Keep every other input at its default and double the [products]. See how k responds.

  1. 01New [Products]: 1
  2. 02Baseline K: 5
  3. 03New K: 10
  4. 04K increases by 100% → use this sensitivity to plan for real-world variation.
03 · PATTERN

[Reactants] halved

rxt = 0.05 (from 0.1)

Keep every other input at its default and halve the [reactants]. See how k responds.

  1. 01New [Reactants]: 0.05
  2. 02Baseline K: 5
  3. 03New K: 10
  4. 04K increases by 100% → use this sensitivity to plan for real-world variation.
04 · PATTERN

[Reactants] doubled

rxt = 0.2 (from 0.1)

Keep every other input at its default and double the [reactants]. See how k responds.

  1. 01New [Reactants]: 0.2
  2. 02Baseline K: 5
  3. 03New K: 2.5
  4. 04K decreases by 50% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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