The effect of change in temperature
   
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  According to Le-chatelier's principle a change in temperature is a stress on an equilibrium system. If at equilibrium the temperature of system is changed the system will no longer at remain at equilibrium. To restore equilibrium, the reaction will in either forward or backward direction.
  By applying Le-chatelier's principle, we can predict the direction of reaction when temperature of an equilibrium system is changed. Effect of change in temperature is related to the nature of reaction whether it is an endothermic reaction or an exothermic reaction.
For endothermic reaction, Kc increases with the increase in temperature.
For exothermic reaction, Kc decreases with the increase in temperature.
Consider a reversible reaction: aA + bB cC + dD
  For endothermic reaction  
  Increase in temperature:
  In an endothermic reaction, an increase in temperature favours the reaction to occur in the forward direction. At equilibrium, the concentration of A and B will decrease and the concentration of C and D will increase.
Decrease in temperature:
In an endothermic reaction, a decrease in temperature favours the reaction to occur in the backward direction. At equilibrium, the concentration of C and D will decrease and the concentration of A and B will increase.
EXAMPLE
 
H2 + I2 + HEAT 2HI
Above example is an endothermic reaction. If we increase the temperature of system, then the equilibrium will shift in the forward direction where more amounts of HI will be obtained and the concentration of H2 and I2 will decrease at equilibrium.
   
EXAMPLE
 
H2 + I2 + HEAT 2HI
In this example a decrease in temperature favours the reaction to occur in the backward direction where more amounts of H2 and I2 will be obtained and the concentration of HI will decrease at equilibrium.
  For exothermic reaction
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  Increase in temperature:
  In an exothermic reaction, an increase in temperature favours the reaction to occur in the backward direction. At equilibrium, the concentration of C and D will decrease and the concentration of A and B will increase.
Decrease in temperature:
In an exothermic reaction, a decrease in temperature favours the reaction to occur in the forward direction. At equilibrium, the concentration of A and B will decrease and the concentration of C and D will increase.
EXAMPLE
 
N2 + 3H2 2NH3 + HEAT
In this example an increase in temperature favours the reaction to occur in the backward direction where more amounts of N2 and H2 will be obtained and the concentration of NH3 will decrease at equilibrium.
   
EXAMPLE
 
N2 + 3H2 2NH3 + HEAT
  In this example a decrease in temperature favours the reaction to occur in the forward direction where more amounts of ammonia will be obtained and the concentration of N2 and H2 will decrease at equilibrium.
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