### Gas Law

Gases are the only state of matter, which can be compressed and expanded. The characteristics of gases can be explained with the help of quantities like pressure, volume and temperature. There are two models to explain the nature of gases named as Real gas and Ideal gas. Following are the laws defined by various researchers to explain the nature of gases. These laws are based on relation between pressure/ temperature/ volumes.

i) Boyle’s Law: Robert Boyle (1627-1691) first defined the law, as pressure is inversely proportional to volume.

PÂµ1/V

P=k/V

PV=k

(P=pressure, V=volume and k=constant for a given mass of the confined gas).

P1V1=k and P2V2=k (P1 and V1: Pressure and volume of gas under a given conditions, P2 and V2: Pressure and volume of gas under different conditions).

\P1V1=P2V2

ii) Charles’s Law:
Jacques Charles (1746-1823) defined this law, as volume of gas is directly proportional to temperature of gas. He observed that oxygen, nitrogen, hydrogen, carbon dioxide, and air expand at a same extent over the same 80-kelvin temperature.

VÂµT

V=kT

V/T=k

(T= temperature)

V1/T1=k and V2/T2=k (V1 and T1: Volume and temperature of gas under a given condition, V2 and T2: Volume and temperature of gas under different conditions).

\V1/T1=V2/T2

iii) Gay-Lussac’s Law:
Joseph Louis Gay-Lussac (1778-1850) observed that pressure exerted by the gas on the container is directly proportional to its temperature.

PÂµT

P=kT

P/T=k

P1/T1=k and P2/T2=k

By taking similar conditions as explained in previous laws.

\P1/T1=P2/T2

Amedeo Avogadro (1776-1856) presented relationship between volume of gas and number molecules when temperature and pressure is held constant. The number of molecules is measured as moles.

VÂµn

V=kn

V/n=k

(n=number of moles of gas= number of molecules/ Avogadroâ€™s number).

\V1/n1=V2/n2

v) Combined Gas Law and Ideal Gas:
Combined law is for the gas, which obeys all the above-mentioned laws (Boyle, Charlesâ€™s and Gay-Lussac’s laws) exactly.

VÂµT/P

PV/T=k

\
P1V1/T1= P2V2/T2

Inclusion of Avogadro’s law in the combined gas law gives ideal gas law. It combines the relation between pressure, volume and temperature as

PV=nRT

n= number of moles

R=universal gas constant (0.08206 (atm.L)/(mol.K))

T=temperature

vi) Dalton Law:
John Dalton in 1801 gave law of partial pressure. The pressure of a mixture of non-reactive gases is equal to the sum of pressures of all the constituent gases.

Pressure total=Pressure1+ Pressure2+—–+Pressure n