Q12.47P - Chemistry: Molecular Nature Of Matter And Change

Question

Which member in each pair of liquids has the higher vapour pressure at a given temperature? Explain. 

(a) ${\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{6}}$ or   ${\mathbf{C}}_{\mathbf{4}}{\mathbf{H}}_{\mathbf{10}}$      (b)  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}$or ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{F}$    (c) ${\mathbf{NH}}_{\mathbf{3}}$ or  _{${\mathbf{PH}}_{\mathbf{3}}$}            

 

Step-by-Step Solution

Answer

1.  ${\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{6}}$ or  ${\mathbf{C}}_{\mathbf{4}}{\mathbf{H}}_{\mathbf{10}}$: The molecule   ${\mathbf{C}}_{\mathbf{4}}{\mathbf{H}}_{\mathbf{10}}$shows more polarizability than${\mathbf{C}}_{\mathbf{4}}{\mathbf{H}}_{\mathbf{10}}$  molecule.
2.  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}$ or  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{F}$:${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{F}$  : The molecule   shows more polarizability than ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{F}$ .
3.  ${\mathbf{NH}}_{\mathbf{3}}$ or  ${\mathbf{PH}}_{\mathbf{3}}$: The molecule  ${\mathbf{PH}}_{\mathbf{3}}$ shows more polarizability than ${\mathbf{NH}}_{\mathbf{3}}$ .

Step 1: Intermolecular Forces

Intermolecular forces are the interaction which are formed by the attraction of the two having opposite charges (partial positive and partial negative charge). The opposite charge are formed by the presence of the electron-negative atom in the molecule. Due to the presence of an electron-negative atom, there is and induced partial positive charge is generated on the electron-positive charge (or less electron-negative charge) atom. There will be an attraction between the both oppositely charges to form a bond.

 

Polarizability can be defined as the ability of the atom which distort the electron cloud of other molecules by the electron of the molecule. 

 

Step 2: Inter-particle interaction Explanation

The inter-particle interaction is a type of attraction between the atoms in the molecule. 

 

(a) ${\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{6}}$ or  ${\mathbf{C}}_{\mathbf{4}}{\mathbf{H}}_{\mathbf{10}}$: The molecule  ${\mathbf{C}}_{\mathbf{4}}{\mathbf{H}}_{\mathbf{10}}$shows more polarizability than ${\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{6}}$ molecule.

The reason behind this is that the size of the cation is smaller as the electron cloud is near to the nucleus whereas the Ca is large in size.

 

(b) ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}$or${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{F}$  : The molecule  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}$ shows more polarizability than${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{F}$  . The reason behind this is that   is larger in size which is proportional to than${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{F}$  . The electron cloud is away from the nucleus which is capable of polarising the electron cloud of the molecule.

 

(c)${\mathbf{NH}}_{\mathbf{3}}$ or  ${\mathbf{PH}}_{\mathbf{3}}$: The molecule ${\mathbf{PH}}_{\mathbf{3}}$  shows more polarizability than ${\mathbf{NH}}_{\mathbf{3}}$ . The reason behind this is that P-atom is larger in size which is proportional to than N-atom. The electron cloud of the P-atom is away from the nucleus which is capable of polarising the electron cloud of the molecule.