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Surface Chemistry question

2013 · Shift 1 · Q6
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  5. /2013 · Shift 1 · Q6

Surface Chemistry question

2013 · Shift 1 · Q6

JEE AdvancedChemistrySurface ChemistryMCQ+3 / −0.75
Methylene blue, from its aqueous solution, is adsorbed on activated charcoal at 25oC. For this process, the correct statement is
  1. A
    The adsorption requires activation at 25oC.
  2. B
    The adsorption is accompanied by a decrease in enthalpy
  3. C
    The adsorption increases with increase of temperature
  4. D
    The adsorption is irreversible
View written solutionFree

Correct answer: B

  1. Identify the type of adsorption

Methylene blue from aqueous solution getting adsorbed on activated charcoal is a typical case of physical adsorption (generally due to van der Waals forces and surface attraction).

  1. Recall key properties of physical adsorption

Physical adsorption generally has these characteristics:

  • It is exothermic.
  • Hence, enthalpy change is negative: ΔH<0\Delta H < 0ΔH<0.
  • It usually does not require significant activation energy.
  • It decreases with increase in temperature, because adsorption is exothermic.
  • It is usually reversible.
  1. Check each option

Option A: The adsorption requires activation at 25∘25^\circ25∘C.

Physical adsorption does not generally require activation energy.

So, A is incorrect.

Option B: The adsorption is accompanied by a decrease in enthalpy

Since adsorption is an exothermic process,

ΔH<0\Delta H < 0ΔH<0

So enthalpy decreases.

Therefore, B is correct.

Option C: The adsorption increases with increase of temperature

Because adsorption is exothermic, increasing temperature opposes adsorption.

So, C is incorrect.

Option D: The adsorption is irreversible

Physical adsorption is generally reversible.

So, D is incorrect.

  1. Final answer

The correct statement is:

B\boxed{\text{B}}B​
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