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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.
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Tool usage guide
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Key facts
Category
Science & Education
Input types
select, number
Output type
text
Sample coverage
4
API ready
Yes
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.
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
1Select the target variable to solve for: dissolved concentration (C), partial pressure (P), or Henry's constant (k_H).
2Choose 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.
3Enter the known numeric values along with your chosen pressure unit (atm, kPa, or torr).
4View 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.
Examples
1. Calculating Dissolved CO₂ in Carbonated Water
Beverage Process Engineer
Background
A quality control engineer needs to verify the dissolved carbon dioxide concentration in bottled soda water under 2.5 atm of headspace pressure.
Problem
Calculate the expected molarity and mass concentration of CO₂ in water at 25 °C.
How to use
Set 'Solve for' to Dissolved concentration C, choose 'CO₂' from the gas presets, and input 2.5 for partial pressure with unit set to 'atm'.
Outcome
Calculates C = 0.085 mol/L and a mass concentration of 3.74085 g/L of dissolved CO₂.
2. Determining Dissolved Oxygen for Aquaculture
Aquatic Biologist
Background
A biologist is measuring oxygen saturation in a fish pond exposed to ambient air with an O₂ partial pressure of 0.21 atm at 25 °C.
Problem
Find the dissolved oxygen level in mg/L to ensure sufficient aeration for fish respiration.
How to use
Select 'Solve for' C, choose 'O₂' from the gas menu, set pressure to 0.21, and select 'atm'.
Outcome
FAQ
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.