Gas Laws | Charles's Law (PHY-SB-25)

Jacques Charles (1746 - 1823)

was a French scientist, physicist, and inventor. He is best known for formulating Charles’s Law in the late 18th century, describing the direct relationship between the volume of a gas and its absolute temperature at constant pressure.

15.2.1 (b) — Charles’s Law

Physics • Chapter 15 — Molecular Theory of Gases

Charles’s Law explains how the volume of a fixed mass of gas changes with temperature when pressure is held constant.

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Charles’s Law states that:

The volume V of a given mass of gas is directly proportional to the absolute temperature T at constant pressure P.

In mathematical form:
V ∝ T (at constant P)
V / T = constant
For two states: V₁ / T₁ = V₂ / T₂

DO YOU KNOW?

The temperature at which the volume of a gas becomes zero and molecular motion ceases is called absolute zero (0 K or -273 °C).

Graphical Representation

At constant pressure, volume vs temperature graph is a straight line extrapolating back to -273 °C (absolute zero).

Volume increases linearly with temperature. Extrapolated line cuts T-axis at -273 °C.

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Key Takeaways

• At constant pressure, V/T = constant.
• As temperature increases, gas volume increases proportionally.
• Graph of V vs T → straight line.
• Absolute zero (0 K, -273 °C) is the point where volume theoretically becomes zero.

Read Boyle’s Law →