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Does amount of dissociation(alpha) depends on Total Pressure? If the Total temperature...

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shihan | Student, Undergraduate | (Level 1) Salutatorian

Posted June 10, 2013 at 12:01 PM via web

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Does amount of dissociation(alpha) depends on Total Pressure? If the Total temperature decreased,how will it affect to the amount of dissociated from a atom of the reaction? Hope you understand.Please help me on this.

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llltkl | College Teacher | (Level 3) Valedictorian

Posted June 10, 2013 at 1:07 PM (Answer #2)

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What I could make out is that you want to know if the degree of dissociation of a particular species varies with external conditions like pressure, temperature etc.

The answer is yes. The equilibrium position of a chemical reaction changes when the conditions under which the reaction takes place change. These conditions include adding or removing reaction products, changing the temperature or changing the pressure. A change in conditions can favour the forward reaction or, the reverse reaction.  Le Chatelier, a French chemist made a generalization to explain the effect of changes in external conditions on the equilibrium. This generalization bears his name. According to Le Chatelier’s principle, "if a system is subjected to a change of concentration, pressure or temperature, the equilibrium shifts in a direction that tends to undo the effect of that change."

The change of pressure has effect only on those equilibria that involve gaseous substances and proceed with a change with the number of moles of gases. Consider the reaction

N2 (g) + 3H2 (g) = 2NH3 (g)

Here total 4 moles of gaseous reactants produce 2 moles of gaseous products. So, an increase in external pressure should favour the forward reaction as the number of gaseous molecules (and hence pressure) falls in this direction, decreasing the degree of dissociation of reactant molecules thereby. A decrease in pressure will have the reverse effect on this reaction.

The same logic applied to temperature explains effect of temperature on degree of dissociation of reactants.

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shihan | Student, Undergraduate | (Level 1) Salutatorian

Posted June 10, 2013 at 2:01 PM (Reply #1)

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Got it! Thank you very much! :)

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shihan | Student, Undergraduate | (Level 1) Salutatorian

Posted June 10, 2013 at 12:04 PM (Answer #1)

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Extremely Sorry i meant if *Total PRESSURE is decreased how will it affect*

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