Energy changes in chemical reactions 0.0 / 5 ? ChemistryEnergy changes in chemical reactionsIGCSEAQA Created by: becky.65Created on: 17-05-16 18:17 What are exothermic reactions? Reactions that transfer energy to the surroundings and heats up its surroundings 1 of 14 Give three examples of exothermic reactions: Combustion, oxidation reactions, neutralisation reactions 2 of 14 What enthalpy change do exothermic reactions have? A negative one 3 of 14 What are endothermic reactions? Reactions that take in energy from the surroundings, therefore causing a decrease in temperature 4 of 14 What enthalpy change do endothermic reactions have? A positive one 5 of 14 Why do thermal decomposition reactions have to be heated continuously? To keep the reaction going 6 of 14 Why do simple calorimeters not give accurate results for the energy realeased? Because much of the energy heats the surroundings 7 of 14 How can we reduce the energy transfers to the surrundings? By doing reactions in an insulated container - like a polystyrene cup 8 of 14 What happens to bonds in endothermic reactions? They are broken 9 of 14 Why does bond breaking cause an endothermic reaction? Because the bond breaking requires more energy than the energy released when new bonds are formed 10 of 14 What happens to bonds in exothermic reactions? They are formed 11 of 14 Why does bond formation cause an exothermic reaction? Because bond forming releases energy which is greater than the energy used in breaking old bonds 12 of 14 What is the activation energy? The minimum energy needed for a reaction to happen 13 of 14 How do catalysts increase the rate of reaction? They provide a different pathway with an activation energy that is lower 14 of 14
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