Question: 64: Shown below are adsorption isotherms for a gas ‘ X ‘ at temperatures \mathrm{T}_{1}, \mathrm{~T}_{2} and \mathrm{T}_{3} :
p and \frac{x}{m} represent pressure and extent of adsorption,
respectively. The correct order of temperatures for the given adsorption is:
(1) T_{1}>T_{2}>T_{3}
(2) \mathrm{T}_{3}>\mathrm{T}_{2}>\mathrm{T}_{1}
(3) \mathrm{T}_{1}=\mathrm{T}_{2}=\mathrm{T}_{3}
(4) \mathrm{T}_{1}=\mathrm{T}_{2}>\mathrm{T}_{3}
Answer: Option (2)
Explanation:
Adsorption of a gas on a solid surface is an exothermic process.
According to Le Chatelier’s principle, increase in temperature decreases the extent of adsorption
because the system shifts in the direction that absorbs heat.
At a given pressure, lower temperature results in greater adsorption,
while higher temperature results in less adsorption.
From the graph, the curve with the highest value of \frac{x}{m}
at a given pressure corresponds to the lowest temperature.
The top curve is labeled \mathrm{T}_{1}, the middle curve is
\mathrm{T}_{2}, and the lowest curve is \mathrm{T}_{3}.
Thus, \mathrm{T}_{1} is the lowest temperature
and \mathrm{T}_{3} is the highest temperature.
Therefore, the correct order of temperatures is:
\mathrm{T}_{3}>\mathrm{T}_{2}>\mathrm{T}_{1}Hence, option (2) is correct.