energy changes

what is an exothermic reaction and what are some examples

an exothermic reaction is one which transfers energy to the surroundings

some examples are combustion, neutralisation and hand warmers

what is an endothermic reaction and what are some examples

An endothermic reaction is one which takes in energy from the surroundings

Some examples are thermal decomposition and sport injury packs

how can you tell if it’s an endo or exo reaction

exo- there will be a rise in temp

endo- there will be a fall in temp

what is bendomexo

breaking bonds is an endothermic reaction

making bonds is an exothermic reaction

what is bond energy

the energy required to break a bond or the energy released when a bond is formed

what is activation energy

the minimum amount of energy needed before a collision will result in a reaction

how are chemical cells made

1)the 2 electrodes must be able to conduct electricity and so are usually 2 metals

2) the electrolyte is a liquid that contains ions that react with electrodes

3) the chemical reactions between the electrodes and the electrolyte set up a charge difference between the electrodes

4) of the electrodes are then connected by a wire the charge is able to flow and electricity is produced. A voltmeter can also be connected to measure the voltage of the cell

what does the voltage of the cell depend on

1) the type of electrodes used as diff metals react differently with the same electrolyte

2) the bigger the difference in reactivity the bigger the voltage of the cell(pd)

what is a battery

2 or more chemical cells connected in series

how can some cells be recharged

by applying an external current

why can some cells not be charged

the reaction can’t be reversed

what is a fuel cell

A cell that uses fuel and oxygen to generate electricity

what is the overall reaction in a hydrogen fuel cell

in an alkaline hydrogen fuel cell what are the half equations

what are advantee of using hydrogen fuel cells

1) fuel cell vehicles don’t produce as many pollutants and other fuels

2) batteries store less energy than fuel cells and so would need to be recharged more often - which can take a long time

what are some disadvantages of using hydrogen fuel cells

Hydrogen is flammable s it’s hard to sore safely

2) hydrogen is a gas so it takes up more soace to store than a rechargeable battery