Question

Diffusion of gases is mainly due to:
A. Newton’s Law of cooling
B. Pressure difference
C. Joule-Kelvin effect
D. A concentration gradient of the molecules.

Answer 1

The diffusion is the non movement of atoms or molecules from highly concentration region to low concentration region. In other words, the movement of atoms or molecules from high chemical potential regions to low chemical potential regions.

Complete step by step solution:
The diffusion means spreading out and intermixing of particles from one substance to another substance. The diffusion occurs in solids, liquids and gases. The diffusion occurs due to movement of particles from a region of higher concentration region to a region of lower concentration till the uniform distribution is attained. Hence diffusion is referred to as movement gradient. So, the driving force for diffusion is usually the concentration gradient.

Hence, option (D) is correct.

Additional Information: 1. By Graham’s law of diffusion rate of diffusion of a gas is inversely proportional to the square root of its molar mass, i.e.
$R = \dfrac{v}{t} \propto \dfrac{1}{{\sqrt M }}$
R$\to$rate of diffusion of gases
V$\to$Volume
t$\to$time
M$\to$molar mass of the gas

2. Fick’s law also concludes the diffusion, Fick’s law states that –

(a) The amount of material flowing through the unit cross-section of a barrier in unit time is known as flux.
So, $J \times A = \dfrac{{dm}}{{dt}}$
J$\to$flux
A$\to$Area of cross-section
dm$\to$amount of material flowed
dt$\to$time

(b) The flux, in turn, is proportional to the concentration gradient.
So, $J \propto \dfrac{{dc}}{{dx}}$
$J = - D\dfrac{{dc}}{{dx}}$
J$\to$flux $\left( {g/c{m^2} - s} \right)$
D$\to$diffusion coefficient $\left( {c{m^2}/s} \right)$
$\dfrac{{dc}}{{dx}} \to$ Concentration gradient
x$\to$ distance of movement of material particles into the medium perpendicular to the surface of the barrier.

Note: Gaseous particles tend to undergo diffusion because they have kinetic energy. Diffusion is faster at higher temperature because the gas molecules have greater kinetic energy.