Question

Mention the factors on which the rate of diffusion of gases depends. Why are similar conditions of temperature and pressure necessary?

Answer 1

• Diffusion is the process of spreading a substance from an area of higher concentration to a lower concentration till a dynamic equilibrium is achieved.

Example: The spreading of the fragrance of perfume in a specific area.

• The volume of the gas diffused in unit time at a certain temperature and pressure through the unit area is called the rate of diffusion of the gas(r).
• According to Graham's law of diffusion, the rates of diffusion of different gases are inversely proportional to the square roots of their densities, under similar conditions of temperature and pressure.

i.e., r = $\frac{1}{\sqrt{\mathrm{d}}}$(at constant temperature and pressure).

• If r₁ and r₂ are rates of diffusion of two gases, M1 and M2 are their molar masses,

$\frac{{\mathrm{r}}_1}{{\mathrm{r}}_2}$∝ $\sqrt{\frac{{\mathrm{M}}_2}{{\mathrm{M}}_1}}$

• The factors affecting the rate of diffusion are

1. The concentration of the gradient

The diffusion of gas mainly depends on the concentration of the gradient of the molecules. Diffusion of gas occurs from higher concentration to lower concentration.

The higher the difference in the concentration faster is the rate of diffusion.

2. Mass of the Particle

The rate of diffusion of the gases is inversely proportional to the square root of their molar masses, it is given by Graham's law,

$\frac{{\mathrm{r}}_1}{{\mathrm{r}}_2}$ ∝ $\sqrt{\frac{{\mathrm{M}}_2}{{\mathrm{M}}_1}}$(at constant temperature and pressure).

3. Temperature

Since the kinetic energy of the gas molecule is proportional to the temperature, an increase in temperature may increase the speed of the movement of gas particles and their rate of diffusion.

i.e. K.E ∝ T

therefore the rate of diffusion r ∝ T