Define Henry’s Law and explain why the solubility of a gas decreases with increasing temperature.

1. Define Henry’s Law and explain why the solubility of a gas decreases with increasing temperature. 1. हेनरी के नियम को परिभाषित कीजिए तथा समझाइए कि तापमान बढ़ने पर गैस की विलेयता क्यों कम हो जाती है। +

Detailed Answer

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 solution.

C ∝ P

C = k_HP

Where:

C = concentration or solubility of the dissolved gas
P = partial pressure of the gas
k_H = Henry’s law constant

Thus, if the partial pressure of a gas increases, more gas dissolves in the liquid, provided the temperature remains constant.

Effect of Temperature on Gas Solubility

The solubility of most gases in liquids decreases when temperature increases.

This happens mainly because the dissolution of gases in liquids is generally an exothermic process. When the temperature is increased, heat is supplied to the system.

According to Le Chatelier’s principle, the equilibrium shifts in the direction that absorbs the added heat. Therefore, the dissolved gas tends to escape from the liquid into the gaseous phase.

Temperature ↑
↓
Kinetic energy of gas molecules ↑
↓
Gas molecules escape more easily from the liquid
↓
Gas solubility ↓

Molecular Explanation

At higher temperatures, gas molecules possess greater kinetic energy. Therefore, the molecules move more rapidly and are more likely to overcome the attractive forces holding them in the liquid.

As a result, more dissolved gas molecules leave the liquid and enter the gas phase. Hence, the equilibrium concentration of the dissolved gas decreases.

Example

Carbon dioxide is much more soluble in cold water than in warm water. Therefore, cold carbonated drinks retain dissolved CO₂ better than warm drinks.

When a carbonated drink is warmed, CO₂ escapes more rapidly, which is why the drink loses its fizz.

Important Exception

The statement that gas solubility decreases with increasing temperature applies to most gases. The exact temperature dependence can vary depending on the gas, solvent and pressure conditions.

Final Answer

Henry’s Law states that at constant temperature, the solubility of a gas in a liquid is directly proportional to its partial pressure: C = k_HP. The solubility of most gases decreases with increasing temperature because gas dissolution is generally exothermic. Heating gives gas molecules more kinetic energy, causing them to escape more readily from the liquid into the gas phase. Therefore, the amount of dissolved gas decreases.

विस्तृत उत्तर

हेनरी का नियम (Henry’s Law) कहता है कि स्थिर तापमान पर किसी द्रव में घुली हुई गैस की विलेयता उस गैस के द्रव के ऊपर उपस्थित आंशिक दाब के समानुपाती होती है।

C ∝ P

C = k_HP

जहाँ:

C = द्रव में घुली गैस की सांद्रता/विलेयता
P = गैस का आंशिक दाब
k_H = हेनरी नियम नियतांक

अर्थात यदि तापमान स्थिर हो और गैस का आंशिक दाब बढ़ाया जाए, तो अधिक मात्रा में गैस द्रव में घुलेगी।

तापमान बढ़ने पर गैस की विलेयता क्यों घटती है?

अधिकांश गैसों की द्रवों में विलेयता तापमान बढ़ने पर कम हो जाती है।

इसका मुख्य कारण यह है कि गैसों का द्रव में घुलना सामान्यतः ऊष्माक्षेपी (exothermic) प्रक्रिया होती है। जब तापमान बढ़ाया जाता है, तो सिस्टम को ऊष्मा प्रदान की जाती है।

Le Chatelier के सिद्धांत के अनुसार equilibrium अतिरिक्त ऊष्मा के प्रभाव को कम करने वाली दिशा में shift करता है। इसलिए घुली हुई गैस द्रव से बाहर निकलकर गैसीय अवस्था में जाने लगती है।

तापमान ↑
↓
गैस अणुओं की गतिज ऊर्जा ↑
↓
अणु द्रव से आसानी से बाहर निकलते हैं
↓
गैस की विलेयता ↓

आणविक कारण

तापमान बढ़ने पर गैस के अणुओं की गतिज ऊर्जा बढ़ जाती है। इसके कारण अणु अधिक तेजी से गति करते हैं और द्रव में उन्हें रोकने वाले आकर्षण बलों को आसानी से पार कर सकते हैं।

इसलिए अधिक संख्या में घुले हुए गैस अणु द्रव से निकलकर गैस अवस्था में चले जाते हैं। परिणामस्वरूप द्रव में घुली गैस की मात्रा कम हो जाती है।

उदाहरण

ठंडे पानी में CO₂ की विलेयता गर्म पानी की तुलना में अधिक होती है। इसलिए cold carbonated drinks में CO₂ अधिक समय तक घुली रहती है।

जब carbonated drink को गर्म किया जाता है, तो CO₂ तेजी से बाहर निकलती है और drink की fizz कम हो जाती है।

महत्वपूर्ण बात

तापमान बढ़ने पर गैस की विलेयता घटने का नियम अधिकांश गैसों पर लागू होता है। वास्तविक प्रभाव गैस, विलायक और दबाव की परिस्थितियों पर निर्भर कर सकता है।

अंतिम उत्तर

हेनरी का नियम कहता है कि स्थिर तापमान पर द्रव में गैस की विलेयता उसके आंशिक दाब के समानुपाती होती है: C = k_HP. अधिकांश गैसों की विलेयता तापमान बढ़ने पर कम हो जाती है क्योंकि गैस का द्रव में घुलना सामान्यतः ऊष्माक्षेपी प्रक्रिया है। तापमान बढ़ने पर गैस अणुओं की गतिज ऊर्जा बढ़ती है और वे द्रव से अधिक आसानी से बाहर निकलते हैं। इसलिए द्रव में घुली गैस की मात्रा कम हो जाती है।

Advertisement

30 Related MCQs 30 संबंधित बहुविकल्पीय प्रश्न

1. Henry’s Law relates the solubility of a gas to its:

A. Atomic mass

B. Partial pressure

C. Density

D. Melting point

Answer: B. Partial pressure

2. The mathematical expression of Henry’s Law is:

A. C = k_HP

B. PV = nRT

C. P = k/C

D. C = P²

Answer: A. C = k_HP

3. According to Henry’s Law, gas solubility increases when pressure:

A. Decreases

B. Increases

C. Becomes zero

D. Remains irrelevant

Answer: B. Increases

4. The solubility of most gases in liquids with increasing temperature:

A. Increases

B. Decreases

C. Remains exactly constant

D. Becomes infinite

Answer: B. Decreases

5. Dissolution of most gases in liquids is generally:

A. Endothermic

B. Exothermic

C. Nuclear

D. Photochemical

Answer: B. Exothermic

6. When temperature increases, gas molecules acquire:

A. Less kinetic energy

B. More kinetic energy

C. No energy

D. Constant zero energy

Answer: B. More kinetic energy

7. Carbon dioxide is more soluble in:

A. Warm water

B. Cold water

C. Boiling water

D. Hot oil

Answer: B. Cold water

8. Warm carbonated drinks lose CO₂ faster because:

A. Gas solubility increases

B. Gas solubility decreases

C. Pressure becomes infinite

D. CO₂ becomes solid

Answer: B. Gas solubility decreases

9. Henry’s Law is applicable at:

A. Constant temperature

B. Constant atomic number

C. Constant mass only

D. Zero pressure only

Answer: A. Constant temperature

10. k_H represents:

A. Henry’s law constant

B. Heat constant

C. Hydrogen constant

D. Kinetic constant

Answer: A. Henry’s law constant

11. Increasing the partial pressure of a gas generally causes its solubility to:

A. Increase

B. Decrease

C. Become zero

D. Remain unaffected

Answer: A. Increase

12. Which principle explains the effect of heat on an equilibrium involving gas dissolution?

A. Le Chatelier’s principle

B. Avogadro’s law

C. Graham’s law

D. Dalton’s law

Answer: A. Le Chatelier’s principle

13. On heating a gas-liquid solution, dissolved gas tends to:

A. Remain completely dissolved

B. Escape into the gas phase

C. Become a solid

D. React with all water molecules

Answer: B. Escape into the gas phase

14. Which gas is commonly used as an example of gas solubility in soft drinks?

A. CO₂

B. He

C. Ne

D. Ar

Answer: A. CO₂

15. The dissolved gas concentration is represented by:

A. C

B. P

C. T

D. V

Answer: A. C

16. If P doubles at constant temperature, according to Henry’s Law C will:

A. Halve

B. Double

C. Become zero

D. Remain unchanged

Answer: B. Double

17. The solubility of gases generally decreases because heating:

A. Reduces molecular motion

B. Increases molecular motion

C. Removes all solvent

D. Changes gas into a metal

Answer: B. Increases molecular motion

18. Which statement is correct?

A. Gas solubility always increases with temperature

B. Most gases become less soluble on heating

C. Gas solubility is independent of pressure

D. Henry’s Law applies only to solids

Answer: B. Most gases become less soluble on heating

19. A cold soft drink retains more CO₂ because:

A. CO₂ is more soluble at lower temperature

B. CO₂ becomes a solid

C. Water disappears

D. Pressure is always zero

Answer: A. CO₂ is more soluble at lower temperature

20. Heating a carbonated beverage causes:

A. More CO₂ dissolution

B. Faster CO₂ escape

C. Formation of nitrogen

D. Formation of oxygen

Answer: B. Faster CO₂ escape

21. Henry’s Law connects gas solubility with:

A. Partial pressure

B. Atomic radius

C. Ionization energy

D. Electronegativity

Answer: A. Partial pressure

22. The symbol P in Henry’s Law represents:

A. Temperature

B. Partial pressure

C. Mass

D. Volume

Answer: B. Partial pressure

23. Increasing temperature generally favours:

A. Retention of dissolved gas

B. Escape of dissolved gas

C. Solidification of gas

D. Formation of solvent

Answer: B. Escape of dissolved gas

24. Gas solubility is generally higher at:

A. Higher temperature

B. Lower temperature

C. Infinite temperature

D. Boiling point only

Answer: B. Lower temperature

25. The process of gas dissolving in liquid is generally:

A. Exothermic

B. Endothermic

C. Nuclear fission

D. Combustion

Answer: A. Exothermic

26. If gas pressure above a liquid is reduced, its solubility generally:

A. Increases

B. Decreases

C. Becomes infinite

D. Becomes independent of pressure

Answer: B. Decreases

27. Which factor does not directly appear in the simple Henry’s Law expression C = k_HP?

A. Gas partial pressure

B. Henry’s constant

C. Gas concentration

D. Atomic number

Answer: D. Atomic number

28. Why do gas molecules escape more easily at higher temperature?

A. Their kinetic energy increases

B. Their mass becomes zero

C. Their atomic number decreases

D. They become liquids

Answer: A. Their kinetic energy increases

29. Which statement about Henry’s Law is correct?

A. It states that gas solubility is proportional to partial pressure at constant temperature

B. It states that gas solubility is proportional to atomic number

C. It applies only to metals

D. It states that pressure has no effect

Answer: A. It states that gas solubility is proportional to partial pressure at constant temperature

30. The best reason for decreased gas solubility on heating is:

A. Gas molecules gain kinetic energy and escape from the liquid more readily

B. Gas molecules lose all kinetic energy

C. Pressure becomes zero in every case

D. Solvent mass becomes zero

Answer: A. Gas molecules gain kinetic energy and escape from the liquid more readily

Advertisement