Edexcel International A Level (IAL) Chemistry (YCH11) - Unit 4 - 13.6 Temperature effect on K-Study Notes - New Syllabus
Edexcel International A Level (IAL) Chemistry (YCH11) -Unit 4 – 13.6 Temperature effect on K- Study Notes- New syllabus
Edexcel International A Level (IAL) Chemistry (YCH11) -Unit 4 – 13.6 Temperature effect on K- Study Notes -International A Level (IAL) Chemistry (YCH11) – per latest Syllabus.
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Edexcel International A Level (IAL) Chemistry (YCH11) -Concise Summary Notes- All Topics
13.6 Effect of Temperature on the Equilibrium Constant (\( \mathrm{K_c} \) and \( \mathrm{K_p} \))
The value of the equilibrium constant depends only on temperature. Changing temperature alters the position of equilibrium and therefore changes the value of \( \mathrm{K_c} \) and \( \mathrm{K_p} \). The direction of this change depends on whether the reaction is exothermic or endothermic.
Key Idea
Increasing temperature favours the endothermic direction of a reaction.
(i) Exothermic Reactions (\( \mathrm{\Delta H < 0} \))
Heat is released in the forward reaction.
Increase in temperature:
- Equilibrium shifts to the left (endothermic direction).
- Fewer products are formed.
- Value of \( \mathrm{K} \) decreases.
Decrease in temperature:
- Equilibrium shifts to the right.
- More products are formed.
- Value of \( \mathrm{K} \) increases.
(ii) Endothermic Reactions (\( \mathrm{\Delta H > 0} \))
Heat is absorbed in the forward reaction.
Increase in temperature:
- Equilibrium shifts to the right.
- More products are formed.
- Value of \( \mathrm{K} \) increases.
Decrease in temperature:
- Equilibrium shifts to the left.
- Fewer products are formed.
- Value of \( \mathrm{K} \) decreases.
Summary
- Exothermic + ↑T → \( \mathrm{K} \) decreases
- Exothermic + ↓T → \( \mathrm{K} \) increases
- Endothermic + ↑T → \( \mathrm{K} \) increases
- Endothermic + ↓T → \( \mathrm{K} \) decreases
Important Notes
- Temperature is the only factor that changes \( \mathrm{K_c} \) and \( \mathrm{K_p} \).
- Changes in concentration or pressure do not affect \( \mathrm{K} \).
- The effect is the same for both homogeneous and heterogeneous systems.
Example 1:
The reaction \( \mathrm{N_2 + 3H_2 \rightleftharpoons 2NH_3} \) is exothermic. Explain how increasing temperature affects \( \mathrm{K_p} \).
▶️ Answer/Explanation
Increasing temperature favours the endothermic (reverse) reaction.
Therefore, equilibrium shifts to the left and fewer \( \mathrm{NH_3} \) molecules are present.
As a result, the value of \( \mathrm{K_p} \) decreases.
Example 2:
A reaction has \( \mathrm{\Delta H > 0} \). Predict how increasing temperature affects \( \mathrm{K_c} \).
▶️ Answer/Explanation
Since the reaction is endothermic, heat is absorbed in the forward direction.
Increasing temperature favours the forward reaction.
More products are formed at equilibrium.
Therefore, the value of \( \mathrm{K_c} \) increases.