---
title: "Gay-Lussac's Law — AP Chemistry Definition & Exam Guide"
description: "Gay-Lussac's Law says gas pressure is directly proportional to absolute temperature at constant volume. It's the P-T piece of PV = nRT in AP Chem Unit 3."
canonical: "https://fiveable.me/ap-chem/key-terms/gay-lussacs-law"
type: "key-term"
subject: "AP Chemistry"
---

# Gay-Lussac's Law — AP Chemistry Definition & Exam Guide

## Definition

Gay-Lussac's Law states that the pressure of a gas is directly proportional to its absolute temperature, provided its volume remains constant.

## Related Study Guides

- [3.4 Ideal Gas Law](/ap-chem/unit-3/ideal-gas-law/study-guide/XINb2AUU6e3c1rGlhBXg)

## Review

### Related Terms

- [Pressure](/ap-chem/key-terms/pressure): This refers to the force exerted per unit area. It’s like how stepping on a Lego hurts more than stepping on a soft toy - same force, but smaller area!
- Pascal (Pa): This is the SI unit for measuring pressure. Just as we measure distance in meters or weight in kilograms, we measure pressure in Pascals.
- Avogadro’s Law: Another gas law which states that equal volumes of all gases at the same temperature and pressure contain an equal number of molecules. Like having two different types of balloons - one filled with helium and another with air - both will have the same number of molecules if they're at the same temperature and pressure.