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
