What is Henry’s Law? Formula, Applications & Everyday Examples
Henry’s law is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. It explains how gases dissolve in liquids, affecting daily life, industry, and environmental processes.
What is Henry’s Law in Chemistry?
A Henry’s law refers to the principle that the amount of a gas dissolved in a liquid at a constant temperature is directly proportional to the partial pressure of that gas above the liquid.
This concept appears in chapters related to gas solubility, physical chemistry, and real-life applications (like carbonated drinks), making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
While Henry's law itself is not a chemical compound but a law, it is mathematically expressed as:
C = kH × P
Where C is the concentration of dissolved gas, kH is Henry’s law constant (unique for each gas-solvent pair and temperature), and P is the partial pressure of the gas. Many common gases like O2, CO2, or N2 obey this law in water and other solvents.
Preparation and Synthesis Methods
Henry's law is not synthesized but observed during the dissolution of gases in liquids. In the laboratory or industry, gases like CO2 are dissolved in drinks by increasing pressure, ensuring the law applies. For accurate measurement, maintain constant temperature and use clean, non-reacting glassware.
Physical Properties of Henry’s Law Systems
- In systems where Henry's law applies, the solubility of the gas depends on gas nature, solvent type, and temperature.
- Most gases are less soluble at higher temperatures.
- The law holds true for non-reactive, dilute solutions where the gas does not ionize or react chemically with the solvent.
Chemical Properties and Reactions
Henry’s law only applies when the gas and solvent do not chemically react. If a gas like ammonia reacts with water, forming ions, the law no longer applies. Otherwise, it predicts only physical dissolution, not chemical change.
Frequent Related Errors
- Confusing Henry’s law with Raoult’s law (for solutions where the solute is a volatile liquid, not a gas).
- Assuming the law applies when the gas reacts chemically with the solvent (it only holds for non-reacting gases).
- Neglecting temperature effect—higher temperatures usually lower gas solubility.
- Forgetting that the Henry’s law constant is different for each gas, solvent, and temperature combination.
Uses of Henry’s Law in Real Life
Henry's law is widely used in industries and our day-to-day life:
- Manufacturing fizzy drinks (carbonation of sodas and sparkling water).
- Deep-sea diving—explains nitrogen narcosis and decompression sickness.
- Breathing at high altitudes or in medical oxygen therapy.
- Treatment of wastewater and purification of drinking water.
- Explaining why fish survive better in cold water (more O2 dissolves at low temperatures).
Relation with Other Chemistry Concepts
Henry’s law is closely related to topics such as Solubility and Raoult's Law, helping students bridge understanding between gas laws, properties of solutions, and phase equilibria. It connects with Dalton's law of partial pressures to explain how gases behave in mixtures and solutions.
Step-by-Step Reaction Example
1. To calculate the solubility of a gas using Henry’s law, first identify the partial pressure of the gas above the liquid.2. Find the value of Henry’s law constant (kH) for the gas in the given solvent and temperature.
3. Multiply kH by the pressure (P) to find concentration (C):
4. Final Answer: This value gives the amount of gas dissolved per unit volume of the solvent.
Lab or Experimental Tips
Remember Henry's law by the rule “solubility of a gas rises with pressure but drops with temperature.” Vedantu educators often use real soda bottle demonstrations in live sessions to make the law memorable and practical for all students.
Try This Yourself
- Write the Henry’s law equation for O2 dissolving in water.
- Explain in your own words why scuba divers must ascend slowly.
- Give two examples of Henry’s law from your daily life.
Final Wrap-Up
We explored Henry’s law—its definition, formula, uses, and its vital role in our everyday life. Understanding this law is crucial for mastering chemical principles of solutions and the behavior of gases.
For more in-depth tips and live learning support, check out Vedantu’s resources and online classes on colligative properties.
FAQs on Henry’s Law Explained: Definition, Formula, and Uses
1. What is Henry's law in simple terms?
Henry's law states that the amount of a gas that dissolves in a liquid is directly proportional to the pressure of that gas above the liquid, as long as the temperature remains constant.
Key Points:
- Higher gas pressure means more gas will dissolve.
- Temperature must be constant for Henry's law to apply.
2. What is the formula of Henry's law?
The Henry's law formula is:
C = kH × P
Where:
- C = Concentration of dissolved gas
- kH = Henry's law constant (depends on gas, solvent, temperature)
- P = Partial pressure of the gas above the liquid
3. What is Henry's law constant value?
Henry's law constant (kH) varies depending on the gas, solvent, and temperature.
Examples:
- For oxygen in water at 298 K, kH ≈ 1.3 × 10-3 mol/L·atm
- For carbon dioxide in water at 298 K, kH ≈ 3.3 × 10-2 mol/L·atm
4. What is the use of Henry's law?
Henry's law helps predict and explain the solubility of gases in liquids for various real-life and industrial applications.
Main uses include:
- Understanding carbonation in soft drinks
- Explaining nitrogen narcosis in scuba diving
- Calculating oxygen diffusion in blood (lungs)
- Designing chemical reactors and gas absorption processes
5. What is Henry's law for lungs?
Henry's law explains how gases like oxygen and carbon dioxide move between the alveoli and blood in the lungs based on their partial pressures.
Key points:
- Gases diffuse from higher to lower partial pressure
- The amount of gas dissolved in blood is proportional to its partial pressure in the alveolar air
6. How does temperature affect Henry's law constant?
Increasing temperature generally causes the Henry's law constant (kH) to increase, which means gas solubility decreases at higher temperatures.
For most gases:
- Higher temperature ⇒ Less gas dissolves in liquid
- This is important when considering gas exchange and processes at different temperatures
7. Why do carbonated drinks go flat when opened?
When a carbonated drink is opened, the pressure above the liquid drops to atmospheric pressure.
As a result:
- Carbon dioxide gas escapes from the liquid until a new equilibrium is reached
- The drink loses its fizz as CO2 comes out, explained by Henry's law
8. What is the physical significance of Henry’s law constant kH?
The Henry’s law constant (kH) measures how easily a specific gas dissolves in a particular solvent at a given temperature.
Key meanings:
- Lower kH: Higher solubility of the gas in the solvent
- Higher kH: Lower solubility
9. Can Henry’s law apply to solids or liquids?
Henry’s law only describes the behavior of gases dissolving in liquids.
- It does not apply to solids or liquids dissolving in each other
- Other laws and principles govern the solubility of solids and liquids
10. What are some real-life examples of Henry’s law?
Common examples of Henry’s law include:
- Carbonation in soft drinks and soda
- Scuba divers experiencing nitrogen absorption and narcosis
- Fish extracting oxygen from water
- Oxygen and carbon dioxide exchange in the lungs
11. What is the relationship between Henry’s law and partial pressure?
Henry’s law uses the partial pressure of a gas to determine how much of the gas will dissolve in a liquid.
- The higher the partial pressure, the greater the amount of gas dissolved, up to equilibrium
- This relationship is key in chemical, biological, and industrial processes
12. When does Henry’s law fail or break down?
Henry’s law may not accurately predict gas solubility when:
- Pressures are extremely high (non-ideal behavior becomes significant)
- The gas reacts chemically with the solvent
- The solution is far from dilute
