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Topic 5 - Energy Transfer in Reactions (Energy transfer (Chemicals store a…
Topic 5 - Energy Transfer in Reactions
Energy transfer
Chemicals store a certain amount of energy - and different chemicals store different amounts. If the products of a reaction store more energy than the original reactants, then they must've taken in energy from the surroundings
But if they store less energy must've been transferred to the surroundings
Energy that is transferred between the reactants and the surroundings during a chemical reaction is usually transferred by heating
Overall amount of energy in the reactants and the surrounding doesn't change - energy is conserved
Exothermic reactions
A reaction that transfers energy to the surroundings
Shown by a rise in temperature in the surroundings
Burning fuels is exothermic
Uses of exothermic reactions
Hand warmers use exothermic oxidation of iron in air to release energy
Self-heating cans of hot chocolate and coffee also rely on exothermic reaction between chemicals
Endothermic reactions
A reaction that takes in energy from the surroundings
Shown by a fall in temp in surroundings
Uses of endothermic reactions
Sports injury pack - cold pack - take in heat and pack becomes very cold
Energy transfer of reactions
Energy transferred during a reaction is proportional to the temperature change of that reaction
Can find temp change of a reaction where at least one reactant is a liquid or solution by taking the temperature of the reactants, mixing everything together in a polystyrene cup and measuring the temperature at the start and end
Biggest problem with taking measurements like this is the amount of energy that's lost to the surroundings - using a polystyrene cup insulates more than a glass beaker, but some energy is still transferred. Putting the cup in a beaker with cotton wool and putting a lid on helps more