The Effect of Changing Temperature (Oxford AQA IGCSE Chemistry) : Revision Note

Revision notes on The Effect of Changing Temperature for the Oxford AQA IGCSE Chemistry syllabus, written by the Chemistry experts at Save My Exams.

Alexandra Brennan

Written by: Alexandra Brennan

Reviewed by: Stewart Hird

Updated on

The Effect of Changing Temperature on Equilibrium

  • We can predict the effect of changes in temperature on systems in equilibrium

  • To make this prediction it is necessary to know whether the reaction is exothermic or endothermic

  • If the temperature is raised:

    • The yield from the endothermic reaction increases

    • The yield from the exothermic reaction decreases

  • If the temperature is lowered:

    • The yield from the endothermic reaction decreases

    • The yield from the exothermic reaction increases

  • When a change in temperature is made to a system, the system will oppose the change

    • E.g. If the temperature is increased, the system will oppose the change by decreasing the temperature

    • It will do this by favouring the endothermic reaction

Worked Example

Iodine monochloride reacts reversibly with chlorine to form iodine trichloride.

The forward reaction is exothermic:

ICl (l) + Cl2 (g) ⇌ ICl3 (s)

dark brown yellow

What colour will the mixture turn when heated? Explain your answer.

Answer:

  • The system will oppose the increase in temperature

    • Increasing the temperature of an equilibrium reaction favours the endothermic reaction

  • If the forward reaction is exothermic, then the backward reaction must be endothermic

  • Therefore, the equilibrium will move to the left and produce more of the reactants

  • This means that the colour of the mixture will become increasingly brown as the temperature increases

Examiner Tips and Tricks

Mark schemes don't usually give you a mark for stating that the system opposes the change but for the explanation of which reaction is favoured and why.

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Alexandra Brennan

Author: Alexandra Brennan

Expertise: Chemistry Content Creator

Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.

Stewart Hird

Reviewer: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.

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