Basic Gas Laws

In a thermodynamic system, there are different types of gas laws used. In this post, we are going to discuss different basic gas laws.

Basic Gas Laws

Different gas laws are

  • Boyle’s law
  • Charles’ law
  • Avogadro’s law
  • Dalton’s law of partial pressure
  • Ideal gas law

Boyle’s Law

Boyle’s law states that, for a mixed mass of gas at constant temperature volume is inversely proportional to pressure.

Mathematically it can be written as pV=constant
This means if you double the pressure, the volume will get halved.
Explanation: Consider the effect of decreasing the volume of a mixed mass of gas at a constant temperature. The pressure is caused by gas molecules hitting the walls of the container. If the volume of the container is very small, the gas molecules will hit the wall more frequently causing an increase in pressure.

Charles’ Law

Charles’ law states that, for a fixed mass of gas at constant pressure, the volume is directly proportional to temperature.

Mathematically can be written as (V/T)=constant
This means if you double the temperature at constant pressure then the volume will be doubled.

Basic gas laws

Consider a fixed mass of gas in a container with a movable barrier as shown in fig. The barrier can move without any resistance. The barrier will settle so that the pressure inside and outside is identical.

Now suppose if we heat the gas, but not the air that is outside. The gas molecules will now move faster and will hit the barrier more frequently. On the other side, air molecules are hitting it exactly as before.

It is obvious that the barrier will be forced to the right and the volume of the gas will increase. This will continue until the pressure inside and outside is the same.
So we have fulfilled what Charles’ law says.

Avogadro’s Law

The number of molecules or atoms in a specific volume of ideal gas is independent of the size or the gas molar mass.

Mathematically it can be stated as (V/n)=k; where V  is the volume of gas, n  is the number of moles of gas and k is a proportionality constant. 

 Dalton’s Law of Partial Pressure

Dalton’s law or the Law of Partial Pressure states that, the total pressure exerted by a mixture of gases is equal to the sum of partial pressures of the gases in the mixture.

Mathematically it can be expressed asPtotal=Pa+Pb+…………

Ideal Gas Law

The ideal gas law is simply expressed as PV=nRT
from which simple gas laws such as Boyle’s law, Charles’ law, Avogadro’s law are derived.

The Ideal Gas Equation

Before we look at the ideal gas equation, let us state four gas variables and a constant for better understanding.
The four gas variables are:
P =Pressure
V =Volume
n = number of moles of gas
T =Temperature
and a constant
R =Gas constant
The ideal gas equation is PV=nRT

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