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

Amedeo Avogadro (1776 - 1856)

was an Italian scientist most noted for his contribution to molecular theory, now called Avogadro’s Law. He also gave his name to Avogadro’s constant, the number of molecules in one mole of a substance.

15.2.1 (c) — Avogadro’s Law

Physics • Chapter 15 — Molecular Theory of Gases

Avogadro’s Law relates the volume of a gas to the number of moles when temperature and pressure are constant.

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Avogadro’s Law states that:

The volume V of a gas is directly proportional to the number of moles n, provided temperature T and pressure P remain constant.

In mathematical form:
V ∝ n (at constant T and P)
V / n = constant
For two states: V₁ / n₁ = V₂ / n₂

DO YOU KNOW?

At standard temperature and pressure (STP), one mole of any gas occupies a volume of 22.4 L. This volume is the same for all ideal gases regardless of their type.

Graphical Representation

At constant temperature and pressure, the graph of volume vs number of moles is a straight line through the origin.

Volume is directly proportional to the number of moles at constant temperature and pressure.

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Key Takeaways

• At constant temperature and pressure, V ∝ n.
• Equal volumes of gases at the same T and P contain equal numbers of molecules.
• Graph of V vs n → straight line through origin.
• At STP, 1 mole of gas = 22.4 L.

Read Charles’s Law →