Question

Which of the following statements is true for adsorption?

• A. It is accompanied by evolution of heat.
• B. It is a bulk phenomenon.
• C. It is independent of surface area.
• D. It is independent of temperature.

Hint:

To remember the difference easily: ADsorption is a Surface phenomenon (think of "Adding onto a table"), while ABsorption is a Bulk phenomenon (think of a sponge swallowing water into its entire volume)!

Answer 1

The Correct Option is A

Step 1: Define adsorption.
Adsorption is the gathering of molecules onto a surface, distinct from absorption where a substance soaks through the whole bulk.
Step 2: Think about the energy change.
When particles stick to the surface, unbalanced surface forces are satisfied and surface energy falls, so heat is released and $\Delta H$ is negative.
Step 3: Judge statement (1).
Because the process is exothermic, adsorption is indeed accompanied by evolution of heat, so this statement is true.
Step 4: Judge statement (2).
Adsorption acts only at the interface, so calling it a bulk phenomenon is false; that describes absorption.
Step 5: Judge statement (3).
More surface area gives more sites, so the extent rises with surface area; it is not independent, making this false.
Step 6: Judge statement (4).
Since the process is exothermic, raising temperature lowers physical adsorption, so it is not temperature independent.
Step 7: Select the true statement.
The only correct claim is that adsorption evolves heat, which is option (1).
\[ \boxed{\text{Adsorption is exothermic } (\Delta H < 0)} \]