Hydrogen is the first element in the periodic table with the symbol ‘H’ and atomic number 1. It is the most abundant element produced in the Big Bang. Its presence in water is not the only reason that it is essential to sustain life, but hydrogen economy is already here, you use hydrogen to power almost everything – from your home to your car.
Properties
Hydrogen gas does not possess any colour. It is odourless and non-metallic gas. It is the lightest of all known elements.
Physical Properties
Existence
It exists as diatomic gas with the molecular formula H2. Most of the hydrogen on earth exists in molecular forms such as water or organic compounds.
Melting and Boiling Point
The melting point of hydrogen is -259.2°C and boiling point is -252.9°C.
States of Hydrogen
Hydrogen exists in two states in the universe, i.e., atomic and plasma states. When present in the plasma state, its electrons and protons are not bound together, which accounts for its high electrical conductivity. Its high emissivity, i.e., producing light from the sun and other stars is also due to the plasma state of hydrogen. Atomic hydrogen is extremely rare on earth. Although hydrogen mostly exists as diatomic hydrogen gas (in its elemental form) on earth, due to its extraordinary lightweight, it escapes the earth’s gravity, and on the earth’s surface, it is mostly found in the form of various chemical compounds, such as water and hydrocarbons.
Isotopes of Hydrogen
Three naturally occurring isotopes of hydrogen are { 1 }_{ H }, { 2 }_{ H }, and { 3 }_{ H }. The highly unstable nuclei { 4 }_{ H } to { 7 }_{ H } have been synthesized in the laboratory. The formal name of { 1 }_{ H } isotope is protium with symbol P, but this name is rarely used in chemistry.The other isotopes of hydrogen, i.e., 2H and 3H are called deuterium and tritium with symbols D and T, respectively 
Chemical Properties
Heat of Combustion
Hydrogen gas is highly flammable, which is inferred from its enthalpy of combustion, i.e., −286 kJ/mol, in the formation of water.
2H2(g) + O2(g) → 2H2O(l) + 572 kJ (286 kJ/mol)
Hydrogen gas explodes with mixtures of air and chlorine, and these reactions may be triggered by spark, heat, or sunlight.
Flammability
Hydrogen burns with pale blue flame, which is nearly invisible in the daylight, and impurities must be added to detect the colour of its flame. The detection sensors must be installed to detect hydrogen leaks, as such leaks can be very dangerous. Hydrogen flames also radiate ultra-violet (UV) radiations, and its overexposure sometimes cause sun-burn like effects, so proper precaution must be taken while handling hydrogen flames.
Reactivity of Hydrogen
Hydrogen-hydrogen bond is very strong with bond dissociation energy of 435.7KJ/mol. When the energy, which is equal to or greater than the dissociation energy of hydrogen, is supplied, one molecule of hydrogen is dissociated into two atoms (H2→2H). Atomic hydrogen is very reactive. It reduces metallic oxides (a reaction that produces metal in its elemental state) and also forms hydrides such as sodium hydride (NaH.)
Hydrocarbons
Hydrocarbons are a vast array of compounds, which are formed by the combination of hydrogen and carbon. These are associated with living things, and hence, called organic compounds. The study of organic compounds is very important in order to understand life on earth. The study of properties of organic compounds forms a different branch in chemistry, organic chemistry.
Other Hydrogen Compounds
The hydrogen compounds are usually called hydrides. It combines with almost every element in the periodic table except with noble gases. It combines with elements that are more electronegative, such as halogens (F, Cl, Br, I) or oxygen, where hydrogen takes partial positive charge (examples include HF, HCl, HBr). It also combines with less electronegative elements, such as metals (alkali metals Li, Na, Rb) and metalloids, where hydrogen takes partial negative charge.
Uses
1. Fertilisers
Hydrogen is the fundamental building block in the manufacturing of ammonia, which further goes into fertilisers. Ammonia is produced on a large scale by the Haber’s Process. This process combines hydrogen and nitrogen together under a range of temperature and pressure in the presence of a metal catalyst. Due to its high energy of evaporation, ammonia is also used in refrigeration plants as an environment friendly and inexpensively produced refrigerant.
Ammonia production by Haber’s Process
2. Oil Refineries
In oil refineries, hydrogen is used to lower the content of sulfur in diesel fuel. This demand has increased as demand for diesel fuel has risen in recent times. The large hydrogen plants in oil refineries generate hydrogen from natural gas or other hydrocarbon fuels. The reasons behind increased hydrogen use in oil refineries include strict regulations that require low sulfur in diesel and increased oil consumption in developing economies.
Oil Refineries
3. In transport
Hydrogen plays a crucial role in the transport sector as it is abundantly available on earth in the form of hydrocarbons, and its oxidation product (water) does not contribute to greenhouse emissions. Such a mode of transport is safe, economic, and environment friendly. If the technical and economic challenges associated with hydrogen are addressed quickly, we can successfully achieve a hydrogen economy in the near future.
4. Aviation
Hydrogen-powered fuel cells are best suitable for aircraft. They can supply electricity to the aircraft electrical system.
5. Electricity Generation
Electricity is generated with the help of fuel cells. A fuel cell combines hydrogen and oxygen to produce electricity, heat, and water. They convert energy produced by a chemical reaction into electrical power. The fuel cell will produce electricity as long as fuel (hydrogen) is supplied. They operate best on pure hydrogen.
6. Domestic Energy
During electricity generation, the heat produced is also used, and the process is called combined heat and power (CHP). The purchase of electricity from the grid can be minimized, or the generated CHP electricity can be fed into the electricity grid and further it can be used for domestic energy purposes. Electrical and thermal fuel cells can achieve efficiencies up to 95 %.
7. Hydrogen in Sun (The ultimate source of energy for the universe)
Sun provides us with heat, light, and energy that is necessary to sustain life on earth. It holds the whole solar system together. So, it is important to understand the overall structure of the sun. Its composition includes gases, i.e., 90 per cent hydrogen, 9 per cent helium, and only 1 per cent of all the other elements such as carbon, nitrogen, oxygen, silicon, and iron. The diameter of the sun is about 1,390,000 kilometres (865,000 miles), and the mass of the sun is about 300,000 times greater than the earth. The temperature at the centre of the sun reaches an incredible 15 million°C. This is the temperature of an exploding hydrogen bomb. It is hot enough to sustain the thermonuclear reactions that convert hydrogen atoms into helium, and such reactions power the sun. In this way, the Sun consumes about 5 billion kilograms (5 million tons) of its nuclear hydrogen fuel every second. The sun has been burning hydrogen at this rate ever since its formation (some 5 billion years ago), and it will continue to burn steadily for at least another 4 billion years.
Major Misuse of Hydrogen as a Thermonuclear weapon
Hydrogen Bomb
“Hydrogen Bomb” is a nuclear weapon. These are more compact in size or lower in size as compared to first-generation atomic bombs. Enormous explosive power in H-bomb results from an uncontrolled self-sustaining chain reaction in which isotopes of hydrogen combines under extremely high temperature to form helium in a process known as nuclear fusion. The very light nuclei of hydrogen atoms are ideal for this fusion process because they carry weak positive charges, and thus, possesses less resistance to overcome. The hydrogen nuclei that combine to form heavier helium nuclei must lose a small portion of their mass (about 0.63%) to adjust in a single larger atom. They lose this mass by converting it completely into energy, according to Albert Einstein’s famous equation, E = mc2. The energy produced in this way results in the explosion of the hydrogen bomb. This explosion produces blast, light, and heat. The intense white light of the explosion can cause permanent blindness to people gazing at it from a distance of dozens of miles.
A visual of thermonuclear explosion by a hydrogen bomb