# What is Graham’s Law?

## What is Graham’s Law of Diffusion and Effusion?

In1829, Thomas Graham, a Scottish Chemist formulated the Graham’s Law of the Diffusion and Effusion of Gases. According to this Law, the rate of Diffusion of different gases, at a constant temperature, is inversely proportional to the square root of its density.

### Formula for Graham’s Law of Diffusion and Effusion

r ∝ 1/(M)½

**where,**

r = rate of diffusion or effusion

M = molar mass

The Molar Mass tells you the number of grams per mole of a compound. The units for molar mass is grams/mole. It indicates the number of atoms, ions, molecules, or formula units present in a particular chemical.

## 3 Fun facts about Graham’s Law

- Our noses can smell because of Graham’s Law. Graham’s Law determines what we smell faster. Some gases travel faster and some gases travel slower.
- Respiration in all living things is based on Graham’s Law, including respiration through skin or lungs.
- You would have noticed balloons lose air from them slowly, even if they haven’t burst? This is because of Diffusion of Gases.

## What is the Ideal or Universal Gas Law?

According to the Universal or Ideal Gas Law, the relationship between the pressure, volume, and temperature for a fixed mass (quantity) of gas is as follows:

- If temperature and pressure are kept constant, then the volume of the gas is directly proportional to the number of molecules of gas.
- If the temperature and volume remain constant, then the pressure of the gas changes directly proportional to the number of molecules of gas present.
- If the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume.
- If the temperature changes and the number of gas molecules are kept constant, then either pressure or volume (or both) will change in direct proportion to the temperature.

### Formula for the Universal or Ideal Gas Law

The formula for the Universal Gas or the Ideal Gas Law is :

PV = nRT

**where,**

p is pressure

V is volume

n is the number of moles

R is the universal gas constant

T is temperature (K)

The Universal or Ideal Gas Law can be derived from the Kinetic Molecular Theory.

## What is Kinetic Molecular Theory?

Kinetic Molecular Theory shows us how individual gas molecules behave or interact with one another.

According to the Kinetic Molecular Theory :

- Molecules are point masses (they have no volume)
- Gas molecules exert no force on each other unless they collide
- Collisions of molecules with each other or the walls of the container do not decrease the energy of the system
- The molecules of a gas are in constant and random motion
- The temperature of a gas depends on its average kinetic energy, that is, the energy of an ideal gas is entirely kinetic.