Energy Changes Flashcards
Exothermic reaction
Reaction which transfers energy to the surroundings (usually by heating)
How to know reaction is exothermic
Rise in temperature
Examples of exothermic reactions
- combustion
- neutralisation reactions
Everyday uses of exothermic reactions
- hand warmers - use oxidation of iron in air with a salt solution catalyst to release energy
- self heating cans of coffee - use reactions between chemicals and their bases
Endothermic reaction
Reaction which takes in energy from surroundings
How to know reaction is endothermic
Fall in temperature
Examples of endothermic reactions
- reaction between citric acid and sodium hydrogencarbonate
- thermal decomposition
Everyday uses of endothermic reactions
- sports injury packs - chemical reaction allows pack to become instantly cooler
Most common type of reaction
Exothermic
Why is exothermic most common type of reaction
Requires less activation energy
Temperature changes practical
- place polystyrene cup surrounded by cotton wool (insulation) in beaker
- add 25cm³ HCL and record temperature with thermometer
- add 5cm³ of NaOH
- stir and record peak temperature
- calculate temperature change
- determine if reaction was exothermic or endothermic
- repeat experiment with different volumes of NaOH
Reaction profile
Diagram that shows relative energies of reactants and products in a reaction and how energy charges over the course of the reaction
Activation energy
Minimum amount of energy reactants need to collide with each other and react
Labels of reaction profile
- title - exothermic/endothermic
- axis - x-reaction progress y-energy
- reactants
- activation energy
- products
- energy released/absorbed
Where is activation energy label on reaction profile
From reactants to peak
