14.7bFree
Your guide: Miss SanaCounts atoms the way you count rupees: carefully.
Gas molecules are always in random motion. Because of this they spread and mix, from where they are crowded to where they are few. This is diffusion, and it happens by itself.
Open a perfume bottle in one corner of a room, and after a while the smell reaches every corner.
At the same temperature, all gases have the same average kinetic energy. So lighter molecules must move faster. Hydrogen is lighter than oxygen, so it diffuses much faster.
Raising the temperature gives particles more kinetic energy, so diffusion speeds up.
Cotton plugs soaked in hydrogen chloride and ammonia solutions go into the two ends of a 100 cm glass tube at the same time.
Where the gases meet, white fumes of ammonium chloride form. HCl has travelled 40.5 cm and ammonia 59.5 cm in the same time.
Ammonia is lighter than hydrogen chloride, so it diffuses faster.
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Gas molecules are always in random motion. Because of this they spread and mix, from where they are crowded to where they are few. This is diffusion, and it happens by itself.
Open a perfume bottle in one corner of a room, and after a while the smell reaches every corner.
At the same temperature, all gases have the same average kinetic energy. So lighter molecules must move faster. Hydrogen is lighter than oxygen, so it diffuses much faster.
Raising the temperature gives particles more kinetic energy, so diffusion speeds up.
Cotton plugs soaked in hydrogen chloride and ammonia solutions go into the two ends of a 100 cm glass tube at the same time.
Where the gases meet, white fumes of ammonium chloride form. HCl has travelled 40.5 cm and ammonia 59.5 cm in the same time.
Ammonia is lighter than hydrogen chloride, so it diffuses faster.
Same temperature, same average kinetic energy. Lighter molecules move faster and diffuse faster.
Q1. Under the same conditions, which of NO2, SO2 and H2S diffuses fastest, and which slowest? (Quick Check 14.5)
H2S is fastest; SO2 is slowest.
Q2. A perfume bottle is opened in a cold room and in a warm room. Where does the smell spread faster?
In the warm room: faster particles mean faster diffusion.
✗ Heavier gas molecules diffuse faster because they push harder.
✓ At the same temperature, lighter molecules move faster and diffuse faster.
✗ The white ring forms in the middle of the tube.
✓ It forms nearer the HCl end, because ammonia travels farther in the same time.
✗ Ammonia's rate compared with HCl is 40.5 ÷ 59.5.
✓ Put ammonia's distance on top: 59.5 ÷ 40.5, which is more than 1.
1. Which gas will diffuse at the fastest rate?
(c) Exercise MCQ 7 (p. 14): H2S (34) is the lightest of the four, so its molecules move fastest.
2. Under the same conditions, which diffuses slowest?
(b) Quick Check 14.5 (p. 12): SO2 (64) is the heaviest of the three.
3. Diffusion is the spreading of particles:
(a) p. 11: from an area of high concentration to one of low concentration.
4. Raising the temperature makes diffusion:
(d) p. 12: particles have more kinetic energy and move faster.
5. In Activity 14.2, where does the white ring of ammonium chloride form?
(c) p. 12: HCl travels only 40.5 cm of the 100 cm tube, so they meet nearer the HCl end.
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