Grade 6 (age 11-12)

Various Gases

The air we breathe looks like nothing, but it is really a mix of gases like nitrogen, oxygen, and carbon dioxide. Nitrogen makes up about 78 percent and oxygen, which we breathe, about 21 percent. Gases are made of tiny particles, so here you can change the temperature and volume to watch them speed up or push harder.

Gases Are Invisible

Temperature50%

💨 Motion of Gas Particles

①Like air, invisible particles are constantly moving

②Higher temperature → particles move faster

③Particles collide and spread in all directions

Gases in the Air

🌬️ Composition of Air

①Air is a mixture of many gases

②Nitrogen is the most (~78%)

③Oxygen is ~21%, needed for respiration

④CO₂ is small but vital for photosynthesis

Volume & Pressure

Volume80%

💡 Volume vs Pressure

①Smaller gas volume → higher pressure

②Pressing a sealed syringe pushes back harder

③Same gas in smaller space → more particle collisions

Summary

Composition of Air

Air = N₂(78%) + O₂(21%) + Others(1%)

Air is a mixture of gases

Properties of Gases

Temp ↑ → particle motion ↑ / Volume ↓ → pressure ↑

Temperature and volume govern gas behavior

🎯 Key Points

①Most of air is N₂ (78%); O₂ is ~21%

②O₂: respiration and combustion

③CO₂: photosynthesis, makes limewater cloudy

④Smaller volume → higher pressure

⑤Higher temp → faster gas particles

Examples and Unit Test

Example 1

Which gas makes up about 78% of the air, and which about 21%?

Air is a mixture of several gases.

Nitrogen is the most abundant at about 78%, followed by oxygen at about 21%.

▸ Nitrogen (~78%), oxygen (~21%)

Air = 78% nitrogen + 21% oxygen + 1% other. Oxygen is used for breathing and burning.

Example 2

You block a syringe and push the plunger, shrinking the gas volume inside. What happens to the pressure, and why?

As the volume shrinks, the same number of gas particles crowd into a smaller space.

The particles hit the walls more often, so the pressure rises.

▸ The pressure rises (more particle collisions in a smaller space)

Volume down → pressure up. A higher temperature makes particles move faster.

Unit-test style

Which statement about gases is correct?

①Oxygen makes up the largest fraction of the air

②Reducing a gas's volume raises its pressure

③Carbon dioxide makes limewater clear

④A higher temperature makes gas particles move slower

⑤Oxygen is used as a raw material for photosynthesis

▸ ② Reducing a gas's volume raises its pressure

When the volume shrinks, particles collide with the walls more often in the smaller space, so pressure rises.

Nitrogen is the most abundant in air (①), carbon dioxide makes limewater cloudy (③), a higher temperature makes particles move faster (④), and the raw material for photosynthesis is carbon dioxide (⑤).

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Weather & Climate

Combustion & Fire Extinguishing