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
Where is energy released/absorbed label on reaction profile
Level with reactants line to products
How to know reaction profile is exothermic
Products are at a lower energy than reactants
How to know reaction profile is exothermic
Products are at lower energy than reactants
How to know reaction profile is exothermic
Products are at lower energy that the reactants
How to know reaction profile is endothermic
Products are at a higher energy than the reactants
What happens in a chemical reaction
Atoms are rearranged as old bonds are broken and new bonds are formed
What is needed to break existing bonds
Energy
What type of process is bonds breaking
Endothermic
What happens when new bonds are formed
Energy is released
What type of process is bond formation
Exothermic
How to calculate energy change calculations
- find energy required to break original bonds
- find energy released by forming new bonds
- energy required to break bonds —energy released by forming bonds
Overall energy change for exothermic reaction
Energy released by forming bonds is greater than energy used to break them
Overall energy change for endothermic reaction
Energy used to break bonds is greater than energy released by forming them
