Properties of Gases

Gases change volume a lot with pressure and temperature. Boyle's law says pressure and volume are inverse at fixed temperature; Charles's law says volume tracks absolute temperature at fixed pressure. Pressing a syringe compresses the gas, and heating expands it, which links to everyday cases of the laws. Adjust the pressure and temperature sliders and watch the volume change with the graphs.

Pressure–Volume Relation (Boyle's Law)

Pressure1 atm

💡 Boyle's Law

①At constant temperature, pressure↑ → volume↓

②Pressure and volume are inversely proportional

③P × V = constant

④Pressing a syringe piston compresses the gas

Temperature–Volume Relation (Charles's Law)

Temperature20°C

🔍 Charles's Law

①At constant pressure, temperature↑ → volume↑

②Higher temperature → more energetic molecules

③They strike the walls harder, expanding the volume

④This is why tire pressure rises in summer!

Boyle's Law Graph

Boyle's Law

P₁V₁ = P₂V₂ (constant temperature)

Pressure × volume is always constant (inverse)

Charles's Law

V₁T₁ = V₂T₂

Volume is proportional to absolute temperature (K)

📐 Gas-Law Summary

①Boyle: P↑ → V↓ (constant T, inverse)

②Charles: T↑ → V↑ (constant P, direct)

③Temperature unit: absolute K = °C + 273

④Faster molecules → higher pressure/volume

Exam Key Points

Core Summary

Boyle: PV = const | Charles: V/T = const

Pressure, volume, and temperature of gases are tightly linked

🎯 Exam Key Points

①Boyle: constant T → P and V inversely proportional

②Charles: constant P → V and T(K) directly proportional

③P-V graph: inverse curve

④V-T graph: straight line through origin

⑤Daily examples: diving (Boyle), hot-air balloon (Charles), snack bag (both)

Examples and Unit Test

Example 1

At constant temperature, a gas has a volume of 6 L at a pressure of 1 atm. If you press it to 2 atm, what is the volume? (Boyle law)

By Boyle law, at constant temperature, P₁V₁ = P₂V₂.

1 × 6 = 2 × V₂, so V₂ = 6 ÷ 2 = 3 L.

▸ 3 L

By Boyle law, at constant temperature pressure and volume are inversely proportional (P₁V₁ = P₂V₂).

Example 2

At constant pressure, how does a balloon volume change in a warm place, and why? (Charles law)

By Charles law, at constant pressure the volume increases as the temperature rises (proportional).

As temperature rises, gas particles move more actively and push the walls harder, so the volume increases and the balloon gets bigger.

▸ The volume increases (because particle motion becomes more active)

By Charles law, at constant pressure a higher temperature gives a larger volume.

Unit-test style

Which statement about the properties of gases is correct?

①At constant temperature, higher pressure gives larger volume

②At constant temperature, pressure and volume are inversely proportional

③At constant pressure, a higher temperature gives a smaller volume

④Boyle law states that pressure and volume are proportional

⑤A gas keeps the same volume even when temperature changes

▸ ② At constant temperature, pressure and volume are inversely proportional

By Boyle law, at constant temperature volume decreases as pressure increases, an inverse relationship.

Higher pressure gives smaller volume (①), at constant pressure higher temperature gives larger volume (③), Boyle law is an inverse relationship (④), and a higher temperature increases gas volume (⑤).

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