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chemical equilibrium

Blazing goIITian

Posted on
7 Apr 2009 14:06:38 IST
Posts: 1243
7 Apr 2009 14:06:38 IST
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chemical equilibrium
Engineering Entrance , JEE Main , JEE Advanced , Chemistry , Physical Chemistry

At equilibrium

ü      Rate of forward reaction = Rate of backward reaction

ü      Concentration of all entities become constant

ü      Dynamic equilibrium

ü      Can be attained in closed container only

ü      Catalyst does not change state of equilibrium but helps in attaining it quickly

ü      Gibb’s free energy is minimum and entropy of universe maximum

ü      Can be achieved from either side

ü      Approach toward equilibrium is spontaneous

Extent of a reaction at equilibrium varies with the experimental condition such as concentration of entities, temperature etc.

Normal melting point: at atm pressure, the temperature at which both liquid and solid phases are at equilibrium.

LAW OF CHEMICAL EQUILIBRIUM

For a general reaction                       aA + bB  cC + dD

 K  = [C]c [D]d [A]a [B]b

This equation is also known as the law of mass action because in earlier days, concentration = active mass.

K  depends only on temperature. It  is independent of concentration of entities, catalyst, addition of inert gas etc.

Consider a reaction                    A B                                k1

And                              B A                                k2

Then k1 = 1/k2

And if                                         A B                                k1                      ;

C D                                k2

And                       A + B C + D                         k

Then   K = k1k2

Effect of temperature on K

K = Ae-Ea/RT

A and Ea are assumed to be temperature independent.

If K1 and K2 are eq. constants at temperatures T1 and T2 respectively then

For endothermic reaction, T is proportional to K

For exothermic reaction,   T is inversely proportional to K

Le – Chetelier’s Principle

" If a system at equilibrium is subjected to a change in its pressure, temperature, concentration etc., the system adjusts itself in such a way to nulify the effect of that change." But the effect may not be nulified completely.

Effect of concentration

concept of reaction quotient(Q)

This ration is calculated at given conditions. If Q>K, reaction shifts in backward direction

If Q=K, reaction is at equilibrium and if Q<K, reaction goes in forward direction.

Effect of Pressure

An increase in Pressure (due to decrease in Volume) favours the reaction in the direction that produces smaller no. of moles of  gaseous substance.

Effect of temperature explained before.

Addition of inert gas at constant pressure

reaction goes in the direction having higher no. of moles. don't apply Le-chetelier.

Blazing goIITian

Joined: 17 Mar 2008 20:56:33 IST
Posts: 1243
7 Apr 2009 22:08:13 IST
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hey kisi ko pasand nahi aya kya? there are no rates or comments?

Scorching goIITian

Joined: 1 Jan 2009 15:26:11 IST
Posts: 246
7 Apr 2009 23:18:00 IST
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gr8..!

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