Question

Which plot is the adsorption isobar for chemisorption where x is the amount of gas adsorbed on mass m (at constant pressure) at temperature T?

• A.

  

• B.

  

• C.

  

• D.

  

Answer 1

The correct option is D

Explanation for correct answer:-

Option (D)

Adsorption isobar:-

• Chemisorption is an adsorption process involving a chemical reaction between the surface and the adsorbate.
• This process too requires activation energy, thus we can say that with an increase in temperature, the chemisorption$\left(\frac{\mathrm{x}}{\mathrm{m}}\right)$ also increases.
• Adsorption is a process that occurs at room temperature thus making it a spontaneous reaction.
• We can also say it is an exothermic reaction.
• According to Le-Chartelier’s principle, as the temperature of an exothermic reaction is increased, the reaction proceeds in a backward direction that is in this case the adsorption decreases.
• Hence with the increase in temperature, $\left(\frac{\mathrm{x}}{\mathrm{m}}\right)$decreases.
• As a result when we combine both these cases if we increase the temperature for the case of chemisorption, the ${\displaystyle \frac{x}{m}}$ increases as heat is absorbed by the particles present in the system in order to achieve the required activation energy which results in higher rates of adsorption.
• On the other hand, after some time $\left(\frac{\mathrm{x}}{\mathrm{m}}\right)$decreases when all the particles have already acquired the amount of activation energy needed, as adsorption is an exothermic process that decreases with an increase in the temperature.
• The graph will be:

• Hence it is the correct option

Therefore, the correct answer is option (D)