Hydrogen is the most abundant element in the universe – all of the hydrogen in the universe has its origin in the first few moments after the Big Bang. It is the third most abundant element on the Earth’s surface after oxygen and silicon.
The Earth’s atmosphere contains very little hydrogen gas – its very low density enables it to escape the Earth’s gravity more easily than denser gases like oxygen.
Most of the Earth’s hydrogen is in the form of chemical compounds such as water and hydrocarbons.
How we use hydrogen
At high temperatures and pressures, hydrogen can combine with nitrogen to form ammonia. This colourless gas with a fishy odour is used extensively in the production of fertilisers and nitric acid.
ammonia: N2(g) + 3H2(g) → 2NH3(g)
ammonium nitrate: NH3(g) + HNO3(l) → NH4NO3(s)
Hydrogen, obtained from methane gas (natural gas) is used in the manufacture of methanol.
CH4(g) + H2O(g) → CO(g) + 3H2(g)
CO(g) + 2H2(g) → CH3OH(l)
Methanol is an important industrial chemical used as a solvent, a fuel and in making other chemicals such as formaldehyde for use in the plastics industry. Methanol can be readily converted into synthetic petrol.
Oil refineries use large amounts of hydrogen in processes such as hydro cracking, where large hydrocarbon molecules are split into smaller, more useful molecules like octane.
In the food industry, hydrogen gas is used to convert oils such as sunflower seed oil into semi-solids for use in spreads like margarine.
Other uses include rocket fuel (Space Shuttle main engine), welding, hydrochloric acid production and reducing metallic ores like tungsten oxide into the pure metal.
Rechargeable batteries are used in a variety of modern day appliances such as cell phones, iPods, cordless power tools and video camcorders.
One of their drawbacks is that, when the chemicals within the battery have been used up, no current can be drawn. Recharging replenishes the chemicals and the battery can be used again, but this is time-consuming and inconvenient.
A fuel cell is designed such that a continuous supply of chemical reactants is available. No recharging is needed, and the cell can run continuously provided there is a constant supply of reactants.
Hydrogen-oxygen fuel cells are lightweight and efficient and produce water as the only waste product. As the cell operates, heat is also produced. This can be captured and put to good use. Fuel cells on board the Space Shuttle deliver the same power as batteries weighing 10 times as much and produce water and heat for the crew to use.
Hydrogen-powered cars using fuel cell technologies are becoming increasingly popular.
Hydrogen in history
Hydrogen gas was first recognised as a substance in its own right by Henry Cavendish in 1766. He referred to it as ‘inflammable air’. In 1783, Antoine Lavoisier gave it the name ‘hydrogen’ from the Greek ‘hydro’, meaning water, and ‘genes’ meaning creator.
Hydrogen-filled balloons and airships provided the first reliable form of air travel. Rigid airships called Zeppelins, filled with hydrogen to provide lift, started commercial flights in 1910. The first non-stop trans-Atlantic flight was made by the British airship R34 in 1919. The best known airship was the Hindenburg, which was destroyed in a mid-air fire over New Jersey, USA, on 6 May 1937. This event signalled the end of commercial travel using hydrogen-filled airships.
Hydrogen plays a vital role in fusion reactions that power stars like our sun. These reactions not only produce heavier elements but also release very large amounts of energy.
The vast amounts of energy emitted by the sun come from nuclear reactions that fuse hydrogen atoms into helium atoms. During this process, scientists have discovered that there is a slight loss of mass during the fusion process.
Using Einstein’s famous equation E=mc2, it is possible to calculate the energy released in this process.
For example if one kilogram of matter is transformed then the energy released is:
E = mc2
= 9 x 1016 joules
= 1 x (3 x 108) x (3 x 108
This amount of energy is sufficient to supply over 2.5 million New Zealand homes with all of their annual energy needs.
It is estimated that the mass of the sun is decreasing at the rate of 4.3 x 109 kg per second. This equates to 3.87 x 1026 joules of energy being radiated each second.
Nature of science
Science is a blend of logic and imagination. In the development of fuel cell technologies, these two features of the human mind play a very prominent role.