Question

(a) What is meant by ‘diffusion’? Give one example of diffusion in gases.
(b) Why do gases diffuse very fast?
(c) Name two gases of air which dissolve in water by diffusion. What is the importance of this process in nature?

Answer 1

Hint: There are many mechanisms or physical processes that help in the transport of substances. Among all, one example is diffusion. It helps to move the molecules or particles of a substance from one place to another. The rate of diffusion depends on the mass of the gases.

Complete answer:
(a) The physical process of transport of molecules or particles from higher concentration to lower concentration is known as diffusion. Diffusion is a passive process as it happens down the concentration gradient. No energy is required in order to carry out the process of diffusion. The substance which is to be diffused can be solid, liquid or gas. The medium in which diffusion is taking place can also be solid, liquid or a gas. Diffusion can occur through a membrane or without a membrane.
In our daily lives, diffusion of gases takes place many times. One such example is inside our body, between our blood stream and alveoli. When we inhale, oxygen enters the lungs and goes into the alveoli. The concentration of oxygen increases in our alveoli. The concentration of oxygen in the blood stream coming in contact with the alveoli is less and the concentration of carbon dioxide is more. Hence the oxygen gas molecules diffuse from the alveoli to the bloodstream and the carbon dioxide gas molecules diffuse from the bloodstream to the alveoli. We pass out the carbon dioxide in the atmosphere when we exhale.
(b) Gases have greater intermolecular space between them and hence each molecule experiences less force of attraction. This makes the gas molecules move randomly and possess higher kinetic energy. So, the gas molecules move with faster speed and therefore, diffuse very fast.
(c) Oxygen and carbon dioxide are the two gases which dissolve in water with the help of diffusion. Dissolved oxygen helps the aquatic animals and fishes in respiration while the dissolved carbon dioxide helps the aquatic plants in order to carry out the process of photosynthesis and make food.

Note:
The rate of diffusion depends on the following factors; temperature, concentration gradient, particle size and area in which diffusion occurs. It is given by Graham’s Law of diffusion.
$\dfrac{{{r_1}}}{{{r_2}}} = \sqrt {\frac{{{M_2}}}{{{M_1}}}} $ where r is the rate of diffusion of the gases 1 and 2 and M is the molecular weight of the gases 1 and 2.