# GAY-LUSSAC'S LAW

#### branchTHERMAL PHYSICS

Coming from GASES
Leading to THE IDEAL GAS LAW
===The pressure of a gas of fixed mass and fixed volume is directly proportional to the gas's absolute temperature.=== Simply put, if a gas's temperature increases, then so does its pressure if the mass and volume of the gas are held constant. The law has a particularly simple mathematical form if the temperature is measured on an absolute scale, such as in kelvins. The law can then be expressed mathematically as: $${P}\propto{T}$$ or $$\frac{P}{T}=k$$ where: P is the pressure of the gas T is the temperature of the gas (measured in kelvin). k is a constant. This law holds true because temperature is a measure of the average kinetic energy of a substance; as the kinetic energy of a gas increases, its particles collide with the container walls more rapidly, thereby exerting increased pressure. For comparing the same substance under two different sets of conditions, the law can be written as: $$\frac{P_1}{T_1}=\frac{P_2}{T_2} \qquad \mathrm{or} \qquad {P_1}{T_2}={P_2}{T_1}.$$ [image:http://upload.wikimedia.org/wikipedia/commons/thumb/8/84/Temperature_Pressure_law.svg/220px-Temperature_Pressure_law.svg.png]
Credit: Tristan O'Hanlon