Acids, equilibrium & kinetics · SL/HL
K or Q expression
Evaluate a K or Q expression from concentrations.
Your values
Number formats & units
Use decimal dots in datasets. Single values also accept decimal commas and scientific notation such as 1.2e-3 or 1.2 × 10⁻³.
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Result & working
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Interpretation & assumptions
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Formula & example
The relationship
What the variables mean
| Symbol | Meaning |
|---|---|
| exponent | Stoichiometric exponent in the chosen concentration expression. |
Worked example
- Numerator terms
- 0.80 2 0.40 1
- Denominator terms
- 0.20 1 0.50 1
- Label
- Q
Q = 2.56
Follow the example steps
- Numerator term: (0.8)^(2) = 0.64
- Numerator term: (0.4)^(1) = 0.4
- Denominator term: (0.2)^(1) = 0.2
- Denominator term: (0.5)^(1) = 0.5
- Q = 0.256 / 0.1 = 2.56
Common mistakes
Coefficients become powers in the expression.
Incorrect approach
A ⇌ 2B: K = 0.2/0.5 = 0.4
Correct approach
K = [B]²/[A] = 0.2²/0.5 = 0.08
More checks before you submit
- Do not include pure solids or pure liquids in expressions where their activity is taken as unity.
- Use equilibrium concentrations for K; otherwise the same form evaluates Q.
Method notes
The numerical expression must match the equilibrium and convention specified in the problem. This generic tool evaluates the expression you enter; it does not decide which species belong in it.