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Energy in Reactions
GCSE chemistry and combined chemistry
Question | Answer |
---|---|
How does the law of conservation of energy apply to chemistry? | In all chemical reactions, energy is either transferred to the surroundings or from the surroundings. |
What is an exothermic reaction? | A reaction where energy is transferred to the surroundings. |
Give two examples of exothermic reactions. | Combustion, respiration |
What happens to the temperature of the surroundings during an exothermic reaction? | They increase. The thermometer is included in "the surroundings" so shows the temperature increasing. |
What is an endothermic reaction? | A reaction where energy is transferred from the surroundings. |
Give two examples of endothermic reactions. | Thermal decomposition reactions, citric acid and sodium hydrogencarbonate. |
What happens to the temperature of the surroundings during an endothermic reaction? | They decrease. The thermometer is included in "the surroundings" so shows the temperature decreasing. |
State two uses of exothermic reactions | Self-heating cans, hand warmers |
State two uses of endothermic reactions | Some cooling sports injury packs |
What are reactants? | The substances involved in a chemical reaction |
What are products? | The substances formed when reactants have a chemical reaction |
What is a reaction profile? | A diagram which shows whether the reactants have more or less energy than the products. |
If the reactants have more energy than the products, what kind of a reaction must have taken place? | An exothermic one. The missing energy has been transferred to the surroundings. |
If the reactants have less energy than the products, what kind of a reaction must have taken place? | An endothermic one. The extra energy has been taken in by the surroundings. |
Is breaking bonds endothermic or exothermic? | Endothermic. Chemical bonds are strong so require energy to break (like when you have to put energy in to separate magnets from each other) |
Is making bonds endothermic or exothermic? | Exothermic. Energy is released when chemical bonds are formed (like how two magnets move together when close and generate kinetic energy) |
How do we work out the overall energy change of a reaction? | Work out the difference between the energy needed to break all the bonds in the reactants and the energy released to form all the bonds in the products. |
If more heat energy is released forming bonds than is required for breaking bonds in a reaction what kind of reaction is it? | exothermic |
If less heat energy is released forming bonds than is required for breaking bonds in a reaction what kind of reaction is it? | endothermic |