Chemical equilibrium

It is of two types:

• Homogeneous
• Heterogeneous

Homogenous: Is that when the reactants and products are in same phase.

Heterogeneous: When reactants and products are in different phase .

Characteristics of K

1. At equilibrium, K is applicable only when concentration of reactants is equal to concentration of products.
2. The value of K is independent of initial concentration of reactants.
3. Equilibrium constant has a definite value for each reaction. This value remains same till the time temperature remains constant.
4. For reversible reaction, K also reverses.
5. Value of K is independent of catalyst.

Application of Equilibrium constant

1. Predicting the extent of reaction: The equilibrium constant is directly proportional to extent of reaction.

• If value of k is large, the reaction goes in forward reaction.
• If value of k is less, the reaction goes in backward reaction.
• If k>10³, the extent in this case is large and a reaction proceed almost to completion.
• If value of k is less than 10^-3, then the reaction proceeds to smaller extent.
• If value of k is between 10^-3 to 10³, then there is a appreciable concentration of reactants and products.

2. Predicting the direction of reaction: It tells us whether the reaction is going towards product or reactant. Reaction quotient = Q.

• If Q<k, then reactants predominate.
• If Q=k, then the reaction is at equilibrium.
• If Q>k, then the products predominate.

3. Calculation of equilibrium constant and concentrations.

K= [Products]/ [Reactants]

Factors affecting state of equilibrium “Le Chartlier’s principle

Le chartlier’s principle: We know that at equilibrium, the state variables become constant. If we disturb any state variable, the reaction gets disturbed and the reaction diverts itself in a direction where disturbance is reduced.

So, according to this “ if any kind of reaction is subjected to any kind of stress, then the reaction proceeds in a direction where the stress gets reduced “.

• Effect of change in concentration : For this consider a reaction:

Substances: electrolytes and non electrolytes

In this part we will study equilibrium between ions .So, before we start let’s learn about types of substances (depending upon whether they conduct electricity or not).

We classify substances in to two types:

• Electrolytes
• Non electrolytes

Electrolytes: The substances which dissociate into ions in solution on passing current.

For example: ABàA⁺ + B^–

Non electrolytes: The substances that do not dissociate into ions, when current is passed through them.

That is AB à on passing current , nothing happens .

Further we can classify electrolytes as:

• Strong electrolyte
• Weak electrolyte

Strong electrolyte: The substances which completely dissociate into ions, when current is passed through them. It means if take an example of AB then on passing current it dissociate completely without leaving AB anywhere in solution .

Example: HCl,H₂SO₄ etc

Weak electrolyte: The substances which do not completely dissociate into ions, when current is passed through them. It means, if take an example of AB then on passing current it dissociate partially and we will find AB also in solution.

Example: Acetic acid CH₃COOH etc