Henry's Law Calculator: c = kH x P

How much gas dissolves in a liquid, from the pressure of the gas above it.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose which quantity you want to find.

Enter the other values in the units shown.

The calculator gives the answer with the formula, the substituted numbers, and the answer in other units.

Formulas used

  • c = k_H P
  • P = \frac{c}{k_H}

Worked example

With the default numbers in the calculator above:

  1. The formula, arranged to find the concentration of the dissolved gas: concentration of the dissolved gas = henry's law constant x partial pressure of the gas
  2. Put the values in (every value in its SI unit): concentration of the dissolved gas = 0.034 x 1
  3. The answer: concentration of the dissolved gas: 0.034 mol/L
  4. The same answer in other units: 34 mmol/L

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: What do you want to find? Partial pressure of the gas; Concentration of the dissolved gas (leave it as it is if this is what you are finding) 0.034 mol/L; Henry's law constant (leave it as it is if this is what you are finding) 0.034 mol/L atm.

  1. The formula, arranged to find the partial pressure of the gas: partial pressure of the gas = (concentration of the dissolved gas) / (henry's law constant)
  2. Put the values in (every value in its SI unit): partial pressure of the gas = (0.034) / (0.034)
  3. The answer: partial pressure of the gas: 1 atm
  4. The same answer in other units: 101.325 kPa; 760 mmHg

Common questions

What is Henry's law?

At constant temperature, the amount of a gas that dissolves in a liquid is proportional to the partial pressure of the gas above the liquid.

Why does a fizzy drink fizz when opened?

Opening the bottle lowers the pressure of the carbon dioxide above the liquid, so less can stay dissolved and it bubbles out.

Does temperature matter?

Yes. The constant gets smaller as the temperature rises, so warm water holds less gas.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any chemistry text (Henry's law and the solubility of gases).

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