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🧪 Chemistry  ·  Surface Chemistry  ·  NEET & JEE

Why does the enthalpy of chemisorption tend to be much higher than that of physisorption, typically 80 to 240 kJ/mol versus 20 to 40 kJ/mol?

Answer: Chemisorption involves actual bond formation, which releases more energy than weak van der Waals attraction.

  • A Chemisorption is said to occur mainly at very low temperatures, which releases extra heat in the majority of cases studied
  • B Chemisorption involves actual bond formation, which releases more energy than weak van der Waals attraction
  • C Physisorption is claimed to involve stronger covalent bonding than chemisorption does as widely reported
  • D Enthalpy values reported for chemisorption are generally measured incorrectly in practice in standard practice

Correct answer: B. Chemisorption involves actual bond formation, which releases more energy than weak van der Waals attraction

Explanation: Because chemisorption forms genuine chemical bonds between adsorbate and adsorbent, it releases substantially more energy than the weak van der Waals interactions of physisorption.

Adsorption Isotherm: x/m vs PressureP (pressure)x/mlow P: x/m ∝ Phigh P: saturation plateauAt high pressure, all surface sites are occupied - the curve flattens (monolayer saturation)

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.

Read the full Surface Chemistry notes →