Energy Changes Flashcards
Exothermic reactions
When the reaction transfers energy to its surroundings
Examples of exothermic reactions
Combustion, respiration, neutralisation
Why is energy transferred in a reaction
Bonds are broken and bonds are made
Examples of endothermic reactions
Ice-packs
Eating sherbet
Activation energy
The miniumum amount of energy for a reaction to take place
What are bond energy measured in
KJ/mol
In endothermic bonds are
Broken
In an exothermic reaction the potential energy at the end
Is less- gives out energy
In an endothermic reaction the potential energy at the end
Is more- takes in energy
What is enthalpy change
Energy change
How to calculate the energy changes in a reaction using bonds
- Write symbol equation and workout the bonds breaking and the bonds being made
- Use the bond energy values provided to workout the energy value of all of the bonds of the reactants
- Workout the value of how much energy is required to form the bonds of the products
- Do the sum of the energy of the bonds broken minus the sum of the energy of the bonds made
How would you affect the temperature changes in reacting solutions
- Place polystyrene cup inside of beakers
- Use measuring cylinder to measure 30cm3 of acid and pour into polystyrene
- Record the temperature of the acid
- Use a strip of metal e.g. magnesium
- Add the solid to the acid and record temp every 10 mins
What does a chemical cell do and what are the 2 types
Convert chemical energy into electrical energy
Rechargeable and non-rechargeable cell
How do non-rechargeable cells work
Produce a voltage until the chemical substances are used up
How do rechargeable cells work
An electrical current is passed through the cell backwards. The chemical reaction is reversed so a voltage can be produced again
