Question

Explain the given reactions with the examples (a) Hydrogenation reaction (b) Oxidation reaction (c) Substitution reaction (d) Saponification reaction (e) Combustion reaction.

Answer 1

(a) Hydrogenation reaction:

In hydrogenation reaction is defined as a reaction in which the addition of hydrogen takes place in the presence of a catalyst.

Example of hydrogenation reaction:

$$\begin{gathered} {\mathrm{CH}}_2={\mathrm{CH}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)\to {\mathrm{CH}}_3-{\mathrm{CH}}_3\left(\mathrm{g}\right) \\ \left(\mathrm{Ethene}\right)\left(\mathrm{Hydrogen}\right)\left(\mathrm{Ethane}\right) \end{gathered}$$

In the above reaction, hydrogen is added to the Ethene molecule, and it gets converted to ethane by breaking a double bond.

(b) Oxidation reaction:

Oxidation reaction can be defined as the addition of oxygen to a compound, loss of electrons, and removal of hydrogen.

1. Example of addition of oxygen :

$$\begin{gathered} 2\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{MgO}\left(\mathrm{s}\right) \\ \mathrm{Magnesium}\mathrm{Oxygen}\mathrm{Magnesium}\mathrm{oxide} \end{gathered}$$

The addition of oxygen to Magnesium forms Magnesium oxide.

2. Example of loss of electrons:

$$\begin{gathered} \mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+\mathrm{Cu}\left(\mathrm{s}\right) \\ \mathrm{Zinc}\mathrm{Copper}\mathrm{sulphate}\mathrm{Zinc}\mathrm{sulphate}\mathrm{Copper} \end{gathered}$$

In the above reaction, zinc loses electrons to form Zinc sulphate.

The oxidation state of Zinc is changed from 0 to +2.

3. Example of removal of hydrogen:

$$\begin{gathered} 2{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)+2{\mathrm{SO}}_2\left(\mathrm{g}\right) \\ \mathrm{Hydrogen}\mathrm{sulphide}\mathrm{Oxygen}\mathrm{Water}\mathrm{Sulphur}\mathrm{dioxide} \end{gathered}$$

Hydrogen sulphide gas reacts with oxygen to form water and Sulphur dioxide. In the above reaction, hydrogen is removed from Hydrogen sulphide to give sulphur dioxide.

(c) Substitution reaction: In this reaction, one functional group in a chemical compound is replaced by another functional group

Example:

:$$\begin{gathered} {\mathrm{CH}}_4\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)\stackrel{}{\to {\mathrm{CH}}_3\mathrm{Cl}\left(\mathrm{g}\right)+\mathrm{HCl}\left(\mathrm{g}\right)} \\ \mathrm{Methane}\mathrm{chlorine}\mathrm{Methyl}\mathrm{chloride}\mathrm{Hydrogen}\mathrm{chloride} \end{gathered}$$

In the above reaction hydrogen is substituted by chlorine.

(d) Saponification reaction: Saponification is the process of converting ester into alcohol and soap by the action of alkali.

In saponification reaction hydrolysis of an ester takes place with a base to give alcohol and sodium or potassium salt of carboxylic acid.

Example:

$$\begin{gathered} {\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5\left(\mathrm{l}\right)+\mathrm{NaOH}{\left(\mathrm{l}\right)}_{}\to {\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}{\left(\mathrm{l}\right)}_{}+{\mathrm{CH}}_3\mathrm{COONa}\left(\mathrm{s}\right) \\ \mathrm{Ethyl}\mathrm{ethanoate}\mathrm{sodium}\mathrm{hydroxide}\mathrm{Ethanol}\mathrm{Sodium}\mathrm{ethanoate} \end{gathered}$$

In the above reaction, ester reacts with a base to form alcohol and salt of carboxylic acid.

(e) Combustion reaction: In combustion reaction substance reacts with oxygen, to form carbon dioxide and water. It is an exothermic reaction.

Example:

$$\begin{gathered} {\mathrm{CH}}_4\left(\mathrm{g}\right)+2{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right) \\ \mathrm{Methane}\mathrm{oxygen}\mathrm{water}\mathrm{carbon}\mathrm{dioxide} \end{gathered}$$

In the above reaction combustion of methane takes place in the presence of oxygen to form carbon dioxide and water.

Hence,

(a)Hydrogenation reaction: It involves the addition of hydrogen.

(b) Oxidation reaction: It involves the addition of oxygen.

(c) Substitution reaction: It involves the substitution of one functional group over another.

(d) Saponification reaction: It involves the formation of soap.

(e) Combustion reaction: It involves a reaction with oxygen releasing energy in the form of heat and light.