# Explain why the value of the equilibrium constant, K, for a given reversible reaction changes when the temperature is increased, but does not change when an inert gas is added to the equilibrium mixture at constant volume.

> IB DP Chemistry Standard Level (2023 syllabus) — R2.3 How far? The extent of chemical change · Explain · 4 marks

## Mark scheme (4 marks)

1. K changes with temperature because a change in temperature alters the rate of the forward and reverse reactions by different amounts / changes the ratio of rate constants kf/kr.
2. The new equilibrium position corresponds to a different ratio of product to reactant concentrations, so K (which is defined by that ratio) has a new value.
3. Adding an inert gas at constant volume does not change the partial pressures or molar concentrations of any reacting species.
4. Because the concentrations/partial pressures of reacting species are unchanged, the equilibrium expression Kc (or Kp) retains the same numerical value, so K does not change.

## Key terms

- [reversible reaction](https://www.gradenine.co.uk/glossary/reversible-reaction)

## Related

- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-value-of-the-15e00063) · Published by Druglandscape Ltd.