Energy Changes & Reversible Reactions (AQA GCSE Chemistry)
Revision Note
Author
StewartExpertise
Chemistry Lead
Energy Changes & Reversible Reactions
- Energy changes also accompany chemical changes and energy can be given out (exothermic) or taken in (endothermic)
- The majority of chemical reactions are exothermic with only a small number being endothermic
- For a reversible reaction, if it is exothermic in one direction then it must be endothermic in the opposite direction
- The amount of energy transferred in either direction is the same
- Reversible reactions can be seen in some hydrated salts
- These are salts that contain water of crystallisation which affects their shape and colour
- Water of crystallisation is the water that is included in the structure of some salts during the crystallisation process
- A common example is copper(II) sulfate which crystallises forming the salt copper(II) sulfate pentahydrate, CuSO4.5H2O
- Water of crystallisation is indicated with a dot written in between the salt and the surrounding water molecules
- Anhydrous salts are those that have lost their water of crystallisation, usually by heating, in which the salt becomes dehydrated
- When anhydrous copper(II) sulfate is added to water, it turns blue and heat is given off so the reaction is exothermic
- When hydrated copper(II) sulfate crystals are heated in a test tube, the blue crystals turn into a white powder and a clear, colourless liquid (water) collects at the top of the test tube
Energy changes & reversible reactions example
Exam Tip
Make sure you know the terms anhydrous, hydrated and water of crystallisation.
You've read 0 of your 0 free revision notes
Get unlimited access
to absolutely everything:
- Downloadable PDFs
- Unlimited Revision Notes
- Topic Questions
- Past Papers
- Model Answers
- Videos (Maths and Science)
Did this page help you?