Equilibrium Constant & Temperature (Edexcel International A Level (IAL) Chemistry) : Revision Note
Changing Conditions - Temperature
Changes in temperature change the equilibrium constants Kc and Kp
For an endothermic reaction such as:
2HI (g) ⇌ H2 (g) + I2 (g)
Kc = 
With an increase in temperature:
[H2] and [I2] increases
[HI] decreases
Because [H2] and [I2] are increasing and [HI] is decreasing, the equilibrium constant increases
For an exothermic reaction such as:
2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
Kc = 
With an increase in temperature:
[SO3] decreases
[SO2] and [O2] increases
Because [SO3] decreases and [SO2] and [O2] increases the equilibrium constant decreases
Worked Example
Increasing Kp
What will increase the value of Kp for the following equilibrium?
2A (g) + B (g) ⇌ 2C (g)
ΔH = +6.5 kJ mol-1
Answer
Only temperature changes permanently affect the value of Kp
An increase in temperature shifts the reaction in favour of the products.
The [ products ] increases and [ reactants ] decreases, therefore, the Kp value increases.
How the equilibrium shifts with temperature changes:
Effect on the value of the equilibrium constant
For a reaction that is exothermic in the forward direction, increasing the temperature pushes the equilibrium from right to left
Therefore, the value of the equilibrium constant will decrease as the ratio of [ products ] to [ reactants ] decreases
Conversely, if the temperature is raised in an endothermic reaction, the value of the equilibrium constant will increase
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