Chemical change

A reaction in which energy is given out to its surroundings tempurature of environment increases

Reaction between acids and metals Combustion of fuels

A reaction in which energy is taken from its surroundings tempurature of environment decreases

Thermal decomposition of carbonates Electrolysis

endothermic

exothermic

It releases heat (exothermic reaction) Bonds are made

Carbon dioxide and water

In rocket engines and fuel cells for cars

It releases more energy per kilogram than any other fuel It does not pollute as it only releases water upon combustion No energy is lost in transmission

Expensive to produce and store High pressure tanks are required to store hydrogen and oxygen in sufficient amount Fuel cells become less efficient at lower tempuratures Dangerous to store

It undergoes decay and gives of heat energy which nuclear power stations harness

It is used to heat water to steam This is used to power turbines to produce electricity

Yes - it doesn’t produce CO2, or nitrogen oxides or sulphur

Expensive to maintain Dangerous - radioactive material can be released in an accident

A fuel cell is an electrochemical cell in which a fuel donates electrons at one electrode and oxygen gains electrons at the other H2 and O2 are pumped through 2 porous electrodes where the half-reactions occur

2H2 –> 4H+ + 4E-

4H+ + O2 + 4E- —> 2H2O

2H2 + O2 –> 2H2O