Bond EnergiesAQA GCSE Chemistry: Flashcards

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What is an exothermic reaction?

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What is an exothermic reaction?: A reaction that transfers energy to the surroundings, so their temperature increases
Give two examples of exothermic reactions.: Combustion and neutralisation (also many oxidation reactions)
What is an endothermic reaction?: A reaction that takes in energy from the surroundings, so their temperature decreases
Give an example of an everyday endothermic reaction application.: Sports injury cold packs
How can you tell if a reaction is exothermic or endothermic experimentally?: By measuring the temperature change of the surroundings — a rise means exothermic, a fall means endothermic
What does a reaction profile show?: The relative energies of reactants and products, and the activation energy needed for the reaction to occur
Define activation energy.: The minimum energy that particles must have when they collide in order to react
On a reaction profile, how do you tell if a reaction is exothermic?: The products are shown at a lower energy level than the reactants
(HT) What happens to energy when bonds are broken?: Energy is taken in (this step is endothermic)
(HT) What happens to energy when bonds are formed?: Energy is released (this step is exothermic)
(HT) When is an overall reaction exothermic in terms of bond energies?: When more energy is released forming new bonds than was used breaking the old ones
(HT) Write the equation for overall energy change using bond energies.: Overall energy change = energy needed to break bonds in reactants − energy released forming bonds in products