What do you understand by the terms: (i) hydrogen economy (ii) hydrogenation (iii) ‘syngas’ (iv) water-gas shift reaction (v) fuel-cell ?

Explanation

(i) Hydrogen economy . The proposal to use hydrogen as a fuel in industry , power plants and possibly also in homes and motor vehicles is called hydrogen economy. The basic principle of hydrogen economy is production , storage asnd trasnportation of energy is the form of liquid or gaseous dihydrogen .
(ii) Hydrogenation means addition of hydrogen across double and triple bonds to form saturated compounds. The vegetable oils such soyabean oil, cotton seed oil, groundnut oil, etc. are called polyunsaturated oils since they contain many C=C bonds. When these oils are exposed to air for prolonged periods, the double bonds present in them undergo oxidation, i.e., develop unpleasant taste. To avoid this, double bonds are hydrogenated . For this purpose, dihydrogen is bubbled through edible oils in presence of finely divided nickel at 473 K when the oils are converted into solid fats.
Vegatable oil `+ H_(2) overset(Ni, 473 K) to ` Vegetable Ghee
THis process is called hdyrogenation or hardening of oils and is used in the manufacture of vegetable ghee like Dalda, Gagan, Rath etc. From vegetables oils. It may, however, be noted that hydrogenation reduces the number of double bonds but does not completely eliminate them.
(iii) Syngas. The mixtures of CO and `H_(2)` are called synthesis gas or syngas. It can be produced by the reaction of steam on hydrocarbon or coke at high temperature in the presence of nickel as catalyst.
`C_(n)H_(2n+2)+ nH_(2)O(g) underset(Ni) overset(1270 K)to nCO+(2n+1)H_(2)`
e.g. `CH_(4)(g) + H_(2)O(g) underset(Ni)overset(1270K)to CO(g) + 3H_(2)(g)`
These days, 'syngas' is produced from sewage, saw dust, scrap, wood, newspapers, etc. The process of producing syngas form coal is called 'coal gasification'
`C(s) + H_(2)O(g) underset(Ni)overset(1270K)to CO(g) + H_(2)(g)`
(iv) Water -gas shift reaction. The amount of hydrogen in water gas can be further increased by oxidising CO to `CO_(2)` by mixing it with steam and passing the mixture over `FeCrO_(4)` as catalyst at 673 K.
`underset("Syngas")ubrace(CO(g) + H_(2)O(g))+ underset("Steam")(H_(2)O(g)) underset(FeCrO_(4))overset(673K)to CO_(2)(g)+ 2H_(2)(g)`
This chemical reaction is which CO of the which CO of the water gas reacts with steam to form `CO_(2)` and more `H_(2)` is called water-gas shift reaction.
(v) Fuel Cell. Fuel cell is a device which converts the energy produced during the combustion of a fuel directly into electrical energy. Dihydrogen is used in hydrogen -oxygen fuel cells for generating electrical energy. It has many advantages over the conventional fossil fuels. It is eco-friendly, i.e., it does not cause and pollution and (ii) Its octane number is about three times than that of gasoline , i.e., it releases three times more energy per unit mass of fuel as compared to gasoline.