Question

Explain following terms.

(i) Hydrogen economy
(ii) Hydrogenation
(iii) Syngas
(iv) Water-gas shift reaction
(v) Fuel-cell

Answer 1

(i) Hydrogen economy is the use of hydrogen in efficient way. Hydrogen is transported and stored in the form of liquid or gas. The energy released by hydrogen is greater than the energy released by petrol. Hydrogen is more eco-friendly. It is used in fuel cells to generate electric power.

(ii) Addition of hydrogen to another reactant is called hydrogenation. This reduces a compound in the presence of a suitable catalyst. For examples, vegetable oils are hydrogenated to fats using hydrogen in presence of Ni catalyst.

(iii) A mixture of CO and hydrogen is known as syngas (synthesis gas or water gas). It is used for manufacturing methanol. It is produced by the action of steam on hydrocarbons or coke at high temperature in the presence of a catalyst.
$C{H}_4\left(g\right)+H_{2}O\left(g\right)\underset{Ni}{\overset{1270K}{\to }}\underset{\text{Syngas}}{CO\left(g\right)+3H_2\left(g\right)}$

(iv) The reaction between CO of syngas and steam in presence of catalyst is called water gas shift reaction.
$CO\left(g\right)+H_{2}O\left(g\right)\underset{Catalyst}{\overset{673K}{\to }}C{O}_2\left(g\right)+H_2\left(g\right)$
This reaction increases the yield of hydrogen obtained from coal gasification reaction as shown below.
$C\left(s\right)+H_{2}O\left(g\right)\to CO\left(g\right)+H_2\left(g\right)$
(v) The galvanic cells in which the energy of combustion of fuels is directly converted into electrical energy are called fuel-cells.
In fuel cells, electricity is produced from fuel in presence of an electrolyte. Usually, hydrogen is used as a fuel as it is eco friendly and releases greater energy per unit mass than other fuels and gasoline. An example of fuel cell is hydrogen oxygen fuel cell.