Question

(a) What is meant by an addition reaction? Give an example (with equation) of an addition reaction of an alkene.
(b) What is added to groundnut oil when it is to be converted to vanaspati ghee?
(c) Which of the two is better for our health : butter or vegetable oil? Why?

Answer 1

(a) When an unsaturated hydrocarbon combines with another substance to form a single product, the reaction is termed as an addition reaction. Addition reactions are undergone by all alkenes and alkynes containing either a double bond or a triple bond.

Example: When ethene (C₂H₄) reacts with hydrogen in the presence of a nickel catalyst, ethane is formed. Addition of hydrogen converts the unsaturated hydrocarbon having a double bond to a saturated hydrocarbon comprising a single bond.

Let us look at the chemical equation of the addition reaction:
${\mathrm{CH}}_2={\mathrm{CH}}_2+{\mathrm{H}}_2\stackrel{}{\to {\mathrm{CH}}_3-{\mathrm{CH}}_3}$

(b) Hydrogen is added to groundnut oil when the latter is to be converted to vanaspati ghee. The process of adding hydrogen to an unsaturated hydrocarbon, to produce a saturated hydrocarbon in the presence of a catalyst, is called hydrogenation.

(c) Vegetable oil is good for our health as it contains unsaturated fatty acids (liquid form). Butter is not good for our health as it comprises saturated fatty acids (solid fat).