Answer: At lower temperatures, gas molecules have less kinetic energy to escape the weak attractive forces holding them to the surface, so increased pressure packs more molecules onto the surface effectively.
- A Pressure is said to have little genuine measurable effect on adsorption at any given fixed temperature, in general practice as frequently described in most textbook accounts
- B At lower temperatures, gas molecules have less kinetic energy to escape the weak attractive forces holding them to the surface, so increased pressure packs more molecules onto the surface effectively
- C Higher ambient temperature is said to usually increase the overall degree of physisorption regardless of whatever pressure happens to be applied, during normal conditions as generally observed
- D Physisorption is said to be largely independent of both the surrounding gas pressure and the ambient temperature in most cases, in typical laboratory settings under usual circumstances
Correct answer: B. At lower temperatures, gas molecules have less kinetic energy to escape the weak attractive forces holding them to the surface, so increased pressure packs more molecules onto the surface effectively
Explanation: Physisorption relies on weak van der Waals forces that are easily overcome by thermal motion. At lower temperature, molecules adsorb more readily, and added pressure further increases surface coverage; at higher temperatures, increased kinetic energy makes desorption more likely despite higher pressure.
A typical adsorption isotherm: x/m (mass adsorbed per gram of adsorbent) rises steeply at low pressure, then flattens into a saturation plateau as the adsorbent surface fills up.
Concept context
Explore the chemistry that happens at interfaces, from catalysts that speed up industrial reactions to colloids like milk, smoke, and gels that surround us every day.