Energy Changes Flashcards
(19 cards)
Activation Energy
Minimum energy needed to start a reaction.
Overcoming repulsive force so they collide with enough energy for the reaction to occur
Exothermic
Exothermic - gives out thermal energy to the surroundings
Endothermic
Endothermic - takes in thermal energy from the surroundings
bond breaking =
endothermic
bond making =
exothermic
energy change in the reaction =
bond energies of reactants - bond energies of products
exothermic means there is
a negative answer
endothermic means there is
a positive answer
a battery
more than one cell connected together
a cell
a device containing electrons immersed in an electrolyte
Chemical Cells
use a chemical reaction to transfer energy by electricity
Simple Cells
can be made by connecting two different metals in contact with an electrolyte
Primary Cells
cannot be recharged - once all chemicals have been reacted the cell must be replaced
Secondary Cells
are rechargeable - a charger passes an electric current through the cell to reverse the reaction. This regenerates original chemicals to start again
Fuel Cells
produce a voltage continuously as long as they are supplied with :
- a constant supply
- oxygen e.g. from the air
What happens to the fuel in fuel cells
- electrochemically oxidised rather than being burned
- reaction takes place at a lower temperature
- energy is released as electrical energy not thermal energy
Alkaline Cell
- cheaper to manufacture
- may end up in landfill sites once fully discharged ; recyclable though its expensive
Rechargeable Cell
- can be recharged many times before being recycled , reducing the use of resources
- costs more to manufacture
Hydrogen Fuel Cell
- easy to maintain
- small size
- water is the only chemical product
- very expensive to manufacture
- need a constant supply of hydrogen fuel which is a flammable gas
