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Physical Chemistry

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14 Aug 2008 22:11:11 IST

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Chemisorption

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Why is high temperature favourable for chemisorption but not so for physisorption?

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Bhaskaryya Baruah

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14 Aug 2008 22:47:21 IST

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in chemisorption strong chemical bond force is present in between adsorbate n adsorbent while in physisorption weak vander waals force is present in between them.Therefore high energy (activation energy n heat energy) is required to start chemisorption but physisorption doesnt require high energy.

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Ashwin Menon

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14 Aug 2008 23:47:47 IST

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that's just the definition... how does it explain anything :S

RISHIPRATIM MAZUMDAR

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14 Aug 2008 23:58:53 IST

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let me try...
see..basically physisorptio is the formation of van der waals force between the surface of the adsorbate and the adsorbent...that takes place almost at the instant these two come in contact...these bonds do not require supply of any amt of energy to get formed.and so get formed almost instantaneously(at room temp)..and are basically very weak interactions......so an increase in temperature causes thir rupture...thus increase in temp decreases the rate of hysisorption...

RISHIPRATIM MAZUMDAR

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15 Aug 2008 00:02:47 IST

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and chemisorptio follows the pathway of a chemical reaction as it involves the formatio of chemical bonds....if you have seen the usual graph of the reaction co-ordinates of a chemical reaction..u will find that in most cases,the reactants need to be raised to a higher energy level(which is called activation) in order for the reaction to take place...in chemisorption,the increase in temp supplies the energy for raising the energy level of reactants to the activation enrgy level...thus it enhances the rate of the reaction.....

Sagar Saxena

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21 Feb 2011 00:52:42 IST

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Comparison between physisorption and chemisorption

2nd comparison is your ans ....

Physisorption (Vander Waal's adsorption)	Chemisorption (Langmuir adsorption)
Low heat of adsorption usually in range of 20-40 kJ/mol	High heat of adsorption in the range of 50-400 kJ/mol
Force of attraction are Vander Waal's forces.	Forces of attraction are chemical bond forces.
It is reversible	It is irreversible
It is usually takes place at *low temperature* and decreases with increasing temperature.	It takes place at *high temperature*.
It is related to the case of liquefication of the gas.	It is not related.
It forms *multimolecular layers*.	It forms *monomolecular layers*.
It does not require any activation energy.	It requires high activation energy.
High pressure is favourable. Decrease of pressure causes *desorption*	High pressure is favourable. Decrease of pressure does not cause desorption.
It is not very specific.	It is highly specific.

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