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Methylene blue, from its aqueous solutio...

Methylene blue, from its aqueous solution is adsorbed on activated charcoal at `25^(@)C.`For this process, the correct statement is

A

The adsorption requires activation at `25^@C`

B

The adsorption is accompanied by a decrease in enthalpy.

C

The adsorption increases with increase of temperature.

D

The adsorption is irreversible.

Text Solution

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The correct Answer is:
To solve the question regarding the adsorption of methylene blue on activated charcoal at 25°C, we need to analyze the statements provided in the context of physical adsorption. ### Step-by-Step Solution: 1. **Understanding Adsorption**: - Adsorption is a surface phenomenon where molecules adhere to the surface of a solid or liquid. In this case, methylene blue is being adsorbed onto activated charcoal. 2. **Type of Adsorption**: - The process described is physical adsorption (physisorption), which involves weak van der Waals forces. This is different from chemical adsorption (chemisorption), which involves stronger chemical bonds. 3. **Enthalpy Change**: - Physical adsorption is typically an exothermic process, meaning it releases heat. Therefore, during the adsorption of methylene blue on activated charcoal, there will be a decrease in enthalpy (ΔH < 0). 4. **Activation Energy**: - Physical adsorption does not require activation energy. It occurs spontaneously as the molecules of methylene blue come into contact with the surface of activated charcoal. 5. **Temperature Dependence**: - Since the process is exothermic, according to Le Chatelier's principle, the adsorption process is favored at lower temperatures. Thus, as the temperature increases, the extent of adsorption decreases. 6. **Reversibility**: - Physical adsorption is generally reversible. This means that the adsorbed molecules can be desorbed from the surface of the adsorbent under certain conditions. ### Conclusion: Based on the analysis above, the correct statement regarding the adsorption of methylene blue on activated charcoal at 25°C is that the adsorption is accompanied by a decrease in enthalpy (exothermic process). ### Correct Answer: - The adsorption is accompanied by a decrease in enthalpy.
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