Henry’s Law – Class 12 Chemistry

Introduction

In chemistry, the solubility of gases in liquids is an important concept, especially when studying solutions. One of the key principles that explains this behavior is Henry’s Law. It helps us understand how gases dissolve in liquids under different conditions of pressure.

Solubility

Solubility is the maximum amount of a substance or solute (solid,liquid or gas) that can dissolve in a given amount of solvent (liquid) at a specific temperature and pressure to form a stable solution.

What is Henry’s Law?

Henry’s Law states that:

"At constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas above the liquid."

In simpler words, the higher the pressure of a gas, the more it dissolves in a liquid.

Mathematical Expression and graph

Important Points to Remember

- The law is applicable mainly to sparingly soluble gases.

- Temperature must remain constant.

- The value of Henry’s constant (kₕ) depends on:

- Nature of the gas

- Nature of the solvent

- Temperature

Factors Affecting Henry’s Law

1. Pressure

- Increasing pressure → increases solubility

- Decreasing pressure → decreases solubility

2. Temperature

- Increase in temperature → decreases gas solubility

- This is because gases tend to escape from the liquid at higher temperatures

Applications of Henry’s Law

1. Carbonated Beverages

Soft drinks like soda contain dissolved CO₂ under high pressure. When the bottle is opened, pressure decreases and gas escapes as bubbles.

2. Scuba Diving

Divers breathe compressed air underwater. If they come up too quickly, dissolved nitrogen forms bubbles in blood, causing a dangerous condition called “the bends.”

3. High Altitude Effects

At high altitudes, atmospheric pressure is low, so less oxygen dissolves in blood. This can cause breathing problems.

Limitations of Henry’s Law

- Does not apply to gases that react chemically with the solvent

- Not valid at very high pressures

- Not suitable for highly soluble gases

Real-Life Example

When we open a cold drink bottle, we hear a “fizz” sound. This happens because carbon dioxide escapes rapidly due to a sudden decrease in pressure — a perfect example of Henry’s Law in action.

Conclusion

Henry’s Law is a simple yet powerful concept that explains how gases dissolve in liquids. It has practical applications in daily life, from soft drinks to medical and environmental science. Understanding this law helps students build a strong foundation in solution chemistry.

Quick Revision

- Henry’s Law: Solubility ∝ Pressure

- Formula: p = Kₕ . x

- Higher pressure → more solubility

- Higher temperature → less solubility

50 MCQs

1–10: Basic Concepts

1. Henry’s law relates to:

A) Solid in liquid
B) Gas in liquid
C) Liquid in gas
D) Solid in gas

2. Henry’s law is applicable at:

A) High temperature
B) Constant temperature
C) Low pressure only
D) Variable temperature

3. The unit of Henry’s constant depends on:

A) Pressure unit
B) Temperature
C) Solvent
D) Gas type

4. According to Henry’s law, solubility is:

A) Inversely proportional to pressure
B) Directly proportional to pressure
C) Independent of pressure
D) Exponential

5. The graph between pressure and solubility is:

A) Curve
B) Straight line
C) Hyperbola
D) Parabola

6. Henry’s law constant is denoted by:

A) K
B) kH
C) H
D) P

7. Increase in pressure leads to:

A) Decrease in solubility
B) No change
C) Increase in solubility
D) First increase then decrease

8. Henry’s law is valid for:

A) Highly soluble gases
B) Sparingly soluble gases
C) Solids
D) Liquids

9. The formula of Henry’s law is:

A) p = kHx
B) V = IR
C) PV = nRT
D) pH = -log[H⁺]

10. Temperature increase causes:

A) Increase in solubility
B) Decrease in solubility
C) No effect
D) First increase then decrease

11–20: Conceptual Understanding

11. Soft drinks follow Henry’s law because they contain:

A) O₂
B) CO₂
C) N₂
D) H₂

12. When a soda bottle is opened, pressure:

A) Increases
B) Decreases
C) Remains same
D) Doubles

13. At high altitudes, oxygen dissolved in blood:

A) Increases
B) Decreases
C) Remains constant
D) Doubles

14. Henry’s constant increases with:

A) Increase in solubility
B) Decrease in solubility
C) No change
D) Pressure only

15. Which gas follows Henry’s law best?

A) Reactive gases
B) Non-reactive gases
C) Solids
D) Liquids

16. Partial pressure refers to:

A) Total pressure
B) Pressure of one gas
C) Liquid pressure
D) Solid pressure

17. The slope of graph (p vs x) is:

A) 1/kH
B) kH
C) x
D) p

18. Henry’s law fails at:

A) Low pressure
B) Moderate pressure
C) Very high pressure
D) Constant temperature

19. Solubility depends on:

A) Pressure
B) Temperature
C) Nature of gas
D) All of these

20. CO₂ is more soluble in:

A) Hot water
B) Cold water
C) No effect
D) Steam

21–30: Applications

21. “The bends” occurs due to:

A) Oxygen bubbles
B) Nitrogen bubbles
C) CO₂ bubbles
D) Hydrogen bubbles

22. Divers use:

A) Pure oxygen
B) Compressed air
C) CO₂
D) Hydrogen

23. Henry’s law helps in:

A) Digestion
B) Respiration
C) Gas solubility
D) Photosynthesis

24. Fish survive in water due to:

A) Dissolved oxygen
B) Nitrogen
C) Hydrogen
D) Helium

25. Bottled drinks are sealed under:

A) Low pressure
B) High pressure
C) Normal pressure
D) Vacuum

26. Opening bottle leads to:

A) Dissolution
B) Gas escape
C) Freezing
D) Evaporation

27. At equilibrium, gas molecules:

A) Stop moving
B) Enter and leave equally
C) Only enter
D) Only leave

28. Blood carries oxygen based on:

A) Boyle’s law
B) Henry’s law
C) Charles law
D) Avogadro law

29. Mountain sickness occurs due to:

A) High pressure
B) Low pressure
C) High temperature
D) Low temperature

30. Industrial application includes:

A) Welding
B) Carbonation
C) Melting
D) Freezing

31–40: Numerical/Advanced

31. If pressure doubles, solubility:

A) Halves
B) Doubles
C) Same
D) Zero

32. If kH increases, solubility:

A) Increases
B) Decreases
C) Same
D) Doubles

33. Unit of kH (pressure form):

A) atm
B) mol
C) kg
D) sec

34. Gas solubility is highest at:

A) Low temp, high pressure
B) High temp, low pressure
C) High temp, high pressure
D) Low temp, low pressure

35. Relationship is:

A) Linear
B) Quadratic
C) Cubic
D) Logarithmic

36. Henry’s law constant varies with:

A) Temperature
B) Pressure
C) Volume
D) Mass

37. Mole fraction increases with:

A) Pressure
B) Temperature
C) Volume
D) Mass

38. At zero pressure, solubility:

A) Maximum
B) Minimum
C) Infinite
D) Constant

39. Law is named after:

A) Dalton
B) Henry
C) Boyle
D) Newton

40. Equation is valid for:

A) Ideal gases
B) Real gases only
C) Liquids
D) Solids

41–50: Mixed Questions

41. Dissolution of gas is:

A) Physical
B) Chemical
C) Nuclear
D) Biological

42. Gas escaping causes:

A) Effervescence
B) Condensation
C) Sublimation
D) Deposition

43. Henry’s law is part of:

A) Thermodynamics
B) Solutions
C) Kinetics
D) Organic

44. Solubility decreases when:

A) Pressure increases
B) Temperature increases
C) Pressure decreases
D) Both B & C

45. kH is constant for:

A) Same gas and solvent at fixed temp
B) All gases
C) All solvents
D) Only liquids

46. Oxygen solubility in water is:

A) High
B) Low
C) Infinite
D) Zero

47. Henry’s law helps explain:

A) Boiling
B) Freezing
C) Gas dissolution
D) Melting

48. Which condition increases solubility?

A) High pressure
B) High temperature
C) Low pressure
D) Vacuum

49. The proportionality constant is:

A) Universal
B) Variable
C) Zero
D) Infinite

50. Gas-liquid equilibrium depends on: