# Gay-Lussac's law

A law stating that the volumes of gases undergoing a reaction at constant pressure and temperature are in a simple ratio to each other and to that of the product. the principle that, for relatively low pressures, the density of an ideal gas at constant pressure varies inversely with the absolute temperature of the gas. The expression Gay-Lussac's law is used for each of the two relationships named after the French chemist Joseph Louis Gay-Lussac and which concern the properties of gases, though it is more usually applied to his law of combining volumes, the first listed here. The first law relates to volumes before and after a chemical reaction while the second concerns the pressure and temperature relationship for a sample of gas often known as Amontons' Law.

Gay-Lussac's law is an ideal gas law where at constant volume, the pressure of an ideal gas is directly proportional to its absolute temperature.

Pi/Ti = Pf/Tf

where

Pi = initial pressure

Ti = initial temperature

Pf = final pressure

Tf = final temperature

The relationship between the pressure (P) and temperature (T) of a given mass of gas at constant volume can be illustrated as follows:

### Examples of Gay-Lussac’s Law

Gay-Lussac’s law can be observed in pressure cooker. The pressure cooker is kept on heater and getting heated, the pressure exerted by the steam inside the container increases. The high temperature and pressure inside the container (cooker) cause the food to cook faster.

The increase in pressure which because of increase in the absolute temperature of a gas kept at a constant volume is shown figure.

The relationship between the pressure (P) and temperature (T)