solubility of gas 2

 Here’s a complete, simplified, CBSE Class 12 student-friendly explanation of the Solubility of a Gas in a Liquid, including the effect of pressure and temperature, Henry’s Law, and its real-life applications — perfect for classroom use or presentations.

💨 Solubility of a Gas in a Liquid

📖 Definition:

The solubility of a gas in a liquid is the amount of gas that can dissolve in a given volume of liquid at a specific temperature and pressure.

🔬 Examples:

  • Oxygen (O₂) dissolves slightly in water → supports aquatic life

  • Hydrogen chloride (HCl) dissolves easily in water → highly soluble

🧠 Factors Affecting Gas Solubility:

1. Effect of Pressure ✅

  • As pressure increases, more gas particles are forced into the liquid, increasing solubility.

📌 This is explained by Henry’s Law:

🧪 Henry’s Law:

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

p=KH⋅xp = K_H \cdot x

Where:

  • p = partial pressure of the gas

  • x = mole fraction of the gas in solution

  • KH = Henry’s law constant

📌 Higher KHK_H ⇒ Lower solubility
📊 Different gases have different values of KHK_H based on their nature.

2. Effect of Temperature 🔥

  • Gas solubility decreases with increase in temperature.

  • Gas dissolution is an exothermic process (releases heat), so adding heat shifts equilibrium backward, reducing solubility.
    📖 This follows Le Chatelier’s Principle.

📘 Why Are Fish Comfortable in Cold Water?

  • Cold water dissolves more oxygen, so aquatic life thrives better in cold temperatures than warm ones.

🧪 Henry’s Law Table (Selected Gases in Water)

Gas Temp (K) KH (kbar) Solubility
CO₂ 298 1.67 Very High
O₂ 293 34.86 Moderate
N₂ 293 76.48 Low
He 293 144.97 Very Low

🚀 Applications of Henry’s Law (CBSE Important)

1. Soft Drinks / Soda

  • CO₂ is dissolved under high pressure to increase solubility.

  • When you open the bottle, pressure drops → gas escapes (fizz sound).

2. Scuba Diving

  • Underwater, pressure is high → more N₂ and O₂ dissolve in blood.

  • When divers come up too fast, pressure drops → gas comes out as bubbles.

  • This causes bends (joint pain, blockage of blood vessels).

  • To avoid this, divers use tanks filled with helium–oxygen mixtures instead of nitrogen.

3. High Altitude (Mountains or Aircrafts)

  • At high altitudes, oxygen pressure is low, so less O₂ dissolves in blood.

  • This leads to anoxia: weakness, dizziness, lack of clear thinking.

📝 Exam Tips (CBSE)

✔️ Always write Henry’s Law with formula
✔️ Mention effect of pressure and temperature
✔️ Give at least 2 applications (e.g. soda, scuba diving, high altitude)
✔️ Include real-life examples like dissolved oxygen in water for aquatic life

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