6.2 Production of energy
-Describe the production of heat energy by burning fuels
Buring fossil fuels, such as coal, natural gas and petroleum (crude oil) produces heat energy.
-Describe hydrogen as a fuel
Pros : Does not produce oxides of nitrogen when buring, the most energy rich fuel, only product of combustion is water.
Cons : Expensive and difficult to store
-Describe radioactive isotopes, such as 235 U, as a source of energy
Heat energy and then electrical energy is produced from nuclear reactors.
-Describe the production of electrical energy from simple cells, i.e. two electrodes in an electrolyte.
Electrons flow from the negative electrode to the positive electrode through the external circuit in an electrolytic fuel cell (also electrolysis).
Zinc electrode, Copper electrode and dilute Sulphuric acid electrolyte are used as an example here.
Since Zinc is more reactive than copper, it is the negative electrode, oxidation takes place (Zn -> Zn2+ + 2e-). The elctrons flows through the external circuit to the Copper electrode, the positive ion from the electrolyte (i.e. Hydrogen ions) gets reduced here.
The greater the difference between the reactivity of the two metal electrodes used, the greater the voltage of the circuit would be.
-Describe the use of hydrogen as a potential fuel reacting with oxygen to generate electricity in a fuel cell
Hydrogen is supplied to the negative electrode : H2 -> 2H+ + 2e-
The electrons flows through the external circuit to the positive electrode.
Oxygen is supplied to the positive electrode : O2 + 2H2O + 4e- -> 4OH-
The ions react to produce water : H+ + OH- -> H2O
The overall reaction is : 2H2 + O2 -> 2H2O
When hydrogen reacts with oxygenm to form water in a fuel cell, electrical energy is procued.
