Chemistry topic 5: energy changes

exothermic

in an exothermic reaction, the energy released from forming new bonds in greater than the energy needed to break existing bonds therefore energy is released into the surroundings in the form of heat

endothermic

in an endothermic reaction, the energy released from forming new bonds is less than the energy needed to break existing bonds therefore energy is taken in from the surroundings in the form of heat

endothermic energy profile

exothermic energy profile

cell

a device that generates electrical energy from chemical energy, it contains two electrodes immersed in an electrolyte

battery

a device that stores chemical energy and converts it into electricity, consists of two or more cells connected in series

non-rechargeable/non-renewable batteries

the chemical reactions stop when one of the reactants has been used up eg. alkaline battery

rechargeable/renewable batteries

-the chemical reactions are reversed when an external current/potential difference is supplied eg. hydrogen fuel cell

-can store less electricity the more charging cycles they go through and will eventually need replacement

-no dangerous fuels required, can produce a greater p.d than a hydrogen fuel cell

energy change =

sum of bonds broken - sum of bonds made

hydrogen fuel cell

-electrochemical cell

-contains hydrogen and oxygen that have been separated through electrolysis, when they recombine this produces a potential difference/ external current

-do not get less efficient the longer they run

-can be a source of drinkable water

-run on hydrogen which is an explosive gas making it difficult to store

-produce a fairly low p.d so several are needed