How many of following pair/s present below in which first species has lower boiling point than second species. (i) C 2 H 5 Cl , C 2 H 5 OH (ii) HCl , HF (iii) NH 3 , H 2 O (iv) He , H 2

Question

How many of following pair/s present below in which first species has lower boiling point than second species.

(i) $C_{2} H_{5} Cl, C_{2} H_{5} OH$

(ii) $HCl, HF$

(iii) $NH_{3}, H_{2} O$

(iv) $He, H_{2}$

(v) 1,3,5-trichlorobenzene, 1,2,3-trichlorobenzene

(vi) o-nitrophenol,p-nitrophenol

(vii) $BF_{3}, BMe_{3}$

TestHub · Accepted Answer

The boiling point depends on intermolecular forces.

(i) $C_{2} H_{5} Cl$ (dipole-dipole) < $C_{2} H_{5} O H$ (hydrogen bonding).

(ii) $H Cl$ (dipole-dipole) < $H F$ (hydrogen bonding).

(iii) $N H_{3}$ (hydrogen bonding) < $H_{2} O$ (stronger hydrogen bonding).

(iv) $He$ (smaller dispersion forces) < $H_{2}$ (larger dispersion forces).

(v) 1,3,5-trichlorobenzene (nonpolar, less efficient packing) < 1,2,3-trichlorobenzene (polar, better packing).

(vi) o-nitrophenol (intramolecular H-bonding) < p-nitrophenol (intermolecular H-bonding).

(vii) $B F_{3}$ (smaller, weaker dispersion forces) < $BM e_{3}$ (larger, stronger dispersion forces).

All seven pairs satisfy the condition.

Chemistry - CHEMICAL BONDING Question with Solution | TestHub