Q12.52P - Chemistry: Molecular Nature Of Matter And Change

Question

Which substance has the higher boiling point? Explain.

a.${\mathbf{CH}}_3\mathbf{OH}$ OR ${\mathbf{CH}}_3{\mathbf{CH}}_3$

b.$\mathbf{FNO}$  OR $\mathbf{ClNO}$

c.

Step-by-Step Solution

Answer

The following substance have higher boiling point:

1. ${\mathbf{CH}}_3\mathbf{OH}$
   
2. $\mathbf{FNO}$
   
3. 
   

Step 1: Intermolecular interactions

The intermolecular interactions include the weak London dispersive forces, ion –dipole, dipole-dipole, H-bonding interactions, etc. Depending on these interactions and their strength, the boiling point of the compound differs.

Step 2: Effect of interactions on the boiling point

1. Ethane has weak intermolecular London dispersive forces whereas methanol has H-bonding interactions in between the molecules. Thus, ethane has low boiling point than methanol.
2. Because, F is more electronegative than Cl, the $\mathbf{FNO}$bond is more polar in comparison to the $\mathbf{ClNO}$. This ensures stronger dipole-dipole interactions in $\mathbf{FNO}$than  $\mathbf{ClNO}$ , thus suggesting high boiling point of $\mathbf{FNO}$ in comparison to $\mathbf{ClNO}$.
3. Because of the electronegativity difference between H and F atom, the -trans compound will ensure more H-bonding interactions than the -cis compound. Thus, the -trans compound have higher boiling point than the -cis compound.