A complete summarised group of documents complete for GCSE Chemistry AQA 9-1. To make these Summaries I used 3 sources: The CGP revision guide, My GCSE Science Videos and Free science lessons videos. I achieved a 9 in GCSE AQA Triple Chemistry.
C5 Energy Changes
Introduction
1. Different chemicals store different amounts of product
2. If products of the reaction store more energy than reactants, energy must’ve been taken in, making
the surroundings colder
3. If they store less- the excess energy was transferred to the surroundings (making it hotter)
4. ENERGY IS CONSERVED IN ALL REACTIONS (energy in the universe stays the same
Exothermic Reactions
Energy is transferred to the environment, this
causes a rise in temperature
Examples:
1. Combustion (burning in air)
2. Neutralisation reactions (acid+ alkali)
3. Oxidisation reactions
Everyday reactions:
1. Hand warmers use oxidation of iron in air
to release energy
2. Self-heating food
Endothermic Reactions
Takes in energy from the environment (products have more energy than initially)
Fall in temperature in the environment
Examples:
1. Citric acid reacting with sodium hydrogen carbonate
2. Thermal
decomposition
Everyday uses:
1. Sports injury packs
Energy transfer Practical
What you need to do
1. Take the temperature of the reactants
2. Mix them in a POLYSTYRENE cup
3. Measure energy at the end of the reaction
Reducing the energy lost in the practical
1. Put the polystyrene cup in a beaker of cotton wool
to insulate it more
2. Put a lid on top to stop energy lost by evaporation
You can also use this method to investigate what effect different variables have on the amount of
energy transferred (mass or concertation of the acid)
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