# Henry's Law Calculator

C = k_H·P in three modes with preset 25 °C Henry constants, molar-mass mass readout and atm/kPa/torr pressure.

> Canonical page: https://elysiatools.com/en/tools/henry-law-calculator

- **Category:** Science & Education

- **Keywords:** henry law, gas solubility, henry constant, dissolved oxygen, carbon dioxide solubility, partial pressure

## Overview

The Henry's Law Calculator computes gas solubility in liquid solutions using the equation C = k_H · P. It supports three solving modes—calculating dissolved concentration, partial pressure, or Henry's constant—with built-in 25 °C constants for common gases, molar mass conversions for mass concentration outputs (g/L or mg/L), and pressure unit selection in atm, kPa, or torr.

## Inputs

- **Solve for** (select)
- **Gas** (select)
- **Custom Henry constant k_H (mol/(L·atm), overrides preset)** (number): e.g. 7.6e-4 for a gas not listed
- **Custom molar mass (g/mol, for the mass readout)** (number): e.g. 28.05 for C₂H₄
- **Partial pressure P** (number): e.g. 2.5 atm inside a soda bottle
- **Pressure unit** (select)
- **Dissolved concentration C (mol/L)** (number): e.g. 8.736e-3

## When to use

- Determining the concentration of dissolved oxygen in aquatic environments under specific atmospheric conditions.
- Calculating carbon dioxide saturation levels and required headspace pressure in carbonated beverage production.
- Deriving experimental Henry's law constants from measured dissolved gas concentrations and partial pressures.

## How it works

- Select the target variable to solve for: dissolved concentration (C), partial pressure (P), or Henry's constant (k_H).
- Choose a preset gas (such as O₂, CO₂, N₂, or CH₄) to auto-fill the 25 °C Henry constant and molar mass, or select 'Custom gas' to enter manual values.
- Enter the known numeric values along with your chosen pressure unit (atm, kPa, or torr).
- View the calculated result in molar concentration (mol/L) and equivalent mass concentration (g/L or mg/L).

## Use cases

- Environmental monitoring: Evaluating dissolved oxygen levels in freshwater streams based on ambient partial pressure.
- Beverage carbonation: Finding the required carbon dioxide tank pressure to achieve target dissolved CO₂ volumes.
- Chemical education: Demonstrating the relationship between gas solubility, atmospheric pressure, and Henry's constants in physical chemistry.

## Frequently asked questions

### What equation does this calculator use?

It uses the linear form of Henry's Law, C = k_H · P, where C is dissolved concentration in mol/L, k_H is Henry's constant in mol/(L·atm), and P is partial pressure.

### What temperature are the preset Henry constants based on?

All preset constants in the gas dropdown are standard values calibrated for pure water at 25 °C.

### Which pressure units are supported?

You can input and compute pressure using atmospheres (atm), kilopascals (kPa), or torricellis (torr).

### Can I calculate the solubility of a gas not listed in the presets?

Yes. Select 'Custom gas' and enter your specific Henry constant (k_H) and optional molar mass (MW).

### How does the tool calculate mass concentration in mg/L or g/L?

It multiplies the dissolved molar concentration (mol/L) by the gas molar mass (g/mol), scaling units appropriately for display.

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