Factors affecting equilibriums and equilibrium constants

Factors affecting equilibriums

these are

1. Temperature
2. Pressure
3. Catalyst
4. Concentration

The effect of the above factors on equilibrium position for the equilibrium mixture can be explained qualitatively by Le Chatelier’s Principles that states that; ‘ if a system in equilibrium is subjected to a change, processes occur which tend to counteract the change imposed’.

Alternatively, ‘if the concentration of one of the reacting substance is altered, the equilibrium will shift in such a way as to oppose the change in concentration’

 

Effect of temperature

The effect of temperature on equilibrium depends on whether the reaction is endothermic or exothermic.

(i) For exothermic reactions (∆H⁰ negative) equilibrium position shifts to the left as temperature rise leading to a reduction in equilibrium constants

(ii)   for endothermic reactions (∆H⁰ positive) equilibrium position shift the right as temperature increases leading to increase in the value of equilibrium constants.

Alternatively, the direction of change is given by Vant Hoff’s Law of mobile equilibrium: “if a system is in equilibrium raising the temperature will favor that reaction which is accompanied by absorption of heat, and lowering temperature will favor that reaction which is accompanied by evolution of heat.

Note that: It must be emphasized that it is only temperature that can alter the equilibrium positions and values of equilibrium constants among the factors states above whereas other factors alter only the equilibrium positions.

 

Effect of a catalyst

Catalysts have no effect on the equilibrium constants  or  because they increase the rate of both forward and backward reaction in an equilibrium equally. However, they increase the rate at which equilibrium is attained.

 

Effect of concentration on equilibrium mixture

Variations in concentration of the reactant at constant temperature has no effect on the value of equilibrium constants  and . However, if the concentration of one of the reacting substance in a reversible equilibrium is altered, the equilibrium will shift in such away as to oppose the change in concentration.

 

Effect of pressure changes on equilibrium

1. Pressure has appreciable effects when at least one of the reactant or product in a reversible reaction is a gas because unlike liquids and solids, gases are compressible.
2. The effect of pressure on equilibrium where reactants and/or products are in gaseous form depends on whether there is change in the number of molecules of the gases as the reaction proceeds from left to right.

• In general, for gaseous reaction in which there is a change in the number of molecules, increase in pressure favors a reaction which produces fewer molecules or number of moles of the products.
• Pressure has no effect on those gaseous reactions in which there is no change in number of molecules as the reaction shifts from left to the right. e.g.

H₂(g) + I₂ (g) ↔        2HI(g)

3. Generally high pressure increases the rate at which equilibrium is attained in gaseous mixture because it increases the rate of collision of the reacting molecules.
4. Pressure has no effect on numerical values of and at constant temperature although the equilibrium concentration of reactants and product can vary over a wide range.

 

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