# Physical Properties, Chemical Properties and Uses of Hydrogen

Physical properties of hydrogen:

– Hydrogen is a colorless, odourless and tasteless gas which is sparingly soluble in water.
– Hydrogen is the lightest gas.
– Density: 0.8987 gram per litre
– Boiling point: -253oC
– Melting point: -259oC
– It can be liquefied and solidified at low temperature and high pressure.

Chemical properties:

1. Action with indicators: It does not show any reaction with litmus and hence is neutral towards litmus paper andother indicators.

2. Combustibility: Hydrogen is a inflammable and combustible gas. It is non supporter of combustion.
It gives pale blue flame in air or oxygen to form water. So, hydrogen is also called water gas.
$$\ce{2H2 + O2->H2O}$$
3. Dissociation: Hydrogen is quiet stable to its high bond energy. It dissociates into atomic hydrogen atoms when heated above1730 o.
$$\ce{ZnSO4->[{>1730^{\circ}C}] 2ZnO + SO2 + O2}$$
4. Reaction with halogen: Hydrogen does not react with halogens at ordinary temperature. But at high temperature in the presence of catalyst, hydrogen react to give their respective halides.
$$\ce{H2 + F2->2HF}$$
$$\ce{H2 + Cl2->2HCl}$$
$$\ce{H2 + Br2->2HBr}$$
$$\ce{H2 + I2->2Hl}$$

Note: The reactivity order of hydrogen with other halides is: F2 > Cl2 > Br2 > I2.

Reaction with metals: It reduces metal oxides to metals, when heated.
$$\ce{CuO + H2->[\Delta]Cu + H2O}$$
$$\ce{ZnO + H2->[\Delta]Zn + H2O}$$
$$\ce{PbO + H2->[\Delta]Pb + H2O}$$
$$\ce{Fe2O3 + 4H2->[\Delta]3Fe + 4H2O}$$

Action with carbon monoxide: Carbon monoxide reacts with hydrogen at about 430 oC and 200 atmospheric pressure in the presence of ZnO and Cr2O3 as a catalyst to give methanol.

$$\ce{CO2 + 2H2->[{430^{\circ}C}][\ce{ZnO/Cr2O3}] \underset{\text{Methanol}}{\ce{CH3OH}}$$

Uses of hydrogen:

– Hydrogen is used for synthesis of ammonia in Haber’s process.
– Hydrogen is used for the manufacture of ethanol, HCl etc.
– It is used in hydrogenation of oil to produce artificial ghee.
– It is used as a reductant in metallurgical process.
– Liquid hydrogen is used as a fuel in rockets and missiles.
– It is used for filling balloons, study of atmosphere etc.

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