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CC15H SC19H
Pearson GCSE Combined and Separate Chemistry Higher
| Question | Answer |
|---|---|
| State what is meant by an exothermic reaction. | A reaction that transfers energy to the surroundings |
| State what is meant by an endothermic reaction | A reaction that absorbs energy from the surroundings |
| What happens to the temperature of the surroundings during an exothermic reaction? | It decreases |
| Describe the reaction profile of an exothermic reaction. | The reactants have more energy than the products, so the reactant line on the graph is higher than the product line |
| Describe the five steps of a practical to measure the energy change | 1. Sit a polystyrene beaker inside a glass beaker 2. Measure the starting temperature of the reactants. 3. Mix the reactants in the beaker 4. Cover with lid fitted with a thermometer 5. Monitor and record the highest or lowest temperature |
| Explain what happens to the bonds in a chemical reaction. | During chemical reactions, chemical bonds in the reactants are broken and bonds in the products are formed |
| State which of bond breaking and bond forming gives out energy (exothermic) and which takes in energy (endothermic) | Bond breaking is Endothermic Bond forming is Exothermic |
| Describe how the energy change in a reaction is linked to bond breaking and bond forming. | The energy change in a reaction is the difference between the energy required to break the bonds in the reactants and the energy released by making bonds in the products |
| In an exothermic reaction which are stronger the bonds in the reactants or the bonds in the products? | The bonds in the products |
| In an endothermic reaction which are stronger the bonds in the reactants or the bonds in the products? | The bonds in the reactants |
| What is the definition of bond strength? | The energy required to break one mole of a particular covalent bond in kJ/mol |
| How do you calculate the energy change in a reaction from bond strengths? | Add up the total strength of old bonds broken and subtract the total strength of new bonds made |
| How do catalysts speed up reactions? | They provide another route for the reaction to take place which has a lower activation energy |
| 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 |
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Davenant Foundation School
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