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Physical Chemistry

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 Joined: 19 Jun 2011 Post: 18
23 Feb 2012 23:01:25 IST
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how is adsorption of a gas related to critical temperature
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how is adsorption of a gas related to critical temperature

Blazing goIITian

Joined: 8 Oct 2008
Posts: 8064
26 Mar 2012 11:08:33 IST
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According to the adsorption behavior, the adsorption of gases on solids can be classified into three temperature ranges relative to $T_{c}$:

1.Subcritical region (T<$T_{c}$)

2.Near-critical region ($T_{c}$<T<$T_{c}$+10)

3.The region T>$T_{c}$+10

Isotherms in the first region will show the feature of subcritical adsorption. Isotherms in the second region will show the feature of mechanism transition. Isotherms in the third region will show the feature of supercritical adsorption. The transition will take a continuous way if the isotherms in both sides of the critical temperature belong to the same type, such as adsorption on microporousactivated carbon. However, discontinuous transition could be observed on isotherms in the second region if there is a transformation of isotherm types, such as adsorption on mesoporous silica gel. The decisive factor in such a classification of adsorption is merely temperature, irrespective of pressure. This is because a fluid cannot undergo a transition to a liquid phase at above-critical temperature, regardless of the pressure applied. This fundamental law determines the different adsorption mechanism for the subcritical and supercritical regions. For the subcritical region, the highest equilibrium pressure of adsorption is the saturation pressure $P_{s}$ of adsorbate. Beyond $P_{s}$ condensation happens. Adsorbate in the adsorbed phase is largely in liquid state, based on which different adsorption and thermodynamic theories as well as their applications were developed. For supercritical region, condensation cannot happen, no matter how great the pressure is.

Blazing goIITian

Joined: 21 Mar 2012
Posts: 1457
1 Apr 2012 22:47:23 IST
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it is just crammed but i give u simple relation it is inversly proportional to critical temprature

Blazing goIITian

Joined: 21 Mar 2012
Posts: 1457
1 Apr 2012 22:50:36 IST
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bcoz higher the critical temperature lesser the gas is liquable so less is adsorption

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