Chapter 2: Problem 175

Directions: Each question contains Statement-1 and Statement-2 and has the following choices (a), (b), (c) and (d), out of which ONLY ONE is correct. (a) Statement- 1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement-1 (b) Statement- 1 is True, Statement- 2 is True; Statement- 2 is NOT a correct explanation for Statement-1 (c) Statement-1 is True, Statement- 2 is False (d) Statement- 1 is False, Statement- 2 is True Statement 1 Boiling point of n-pentane is higher than that of neopentane while the melting point of \(n\) -pentane is lower than that of neopentane. and Statement 2 Boiling point of alkanes depend upon the surface area while melting point depends upon the packing of molecules in the solid state. Neopentane fits into the crystal lattice more readily and it has minimum surface area compared to n-pentane.

Short Answer

Expert verified

(a) Statement- 1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement-1 (b) Statement- 1 is True, Statement- 2 is True; Statement- 2 is not a correct explanation for Statement- 1 (c) Statement- 1 is True, Statement- 2 is False (d) Statement- 1 is False, Statement- 2 is True Answer: (a) Statement- 1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement-1

Step by step solution

To begin with, let's confirm the properties of n-pentane and neopentane. n-Pentane is a straight-chain alkane, while neopentane is a branched alkane. Straight-chain alkanes generally have a larger surface area compared to their branched counterparts. #step2#: Examine the effect of surface area on boiling point

As per Statement 2, the boiling point of alkanes depends upon the surface area. Generally, alkanes with larger surface area have a higher boiling point due to increased van der Waals forces. Since n-pentane has a greater surface area than neopentane, its boiling point should be higher than neopentane. This is in agreement with Statement 1. #step3#: Examine the effect of molecular packing on melting point

Statement 2 also states that the melting point depends on the packing of molecules in the solid state. Branched alkanes typically fit into the crystal lattice more readily because of their more symmetrical structure, and hence, have higher melting points. In this case, neopentane, being a branched alkane, fits into the crystal lattice better than n-pentane and thus should have a higher melting point. This also agrees with the Statement 1. #step4#: Determine the correct option

Since both Statement 1 and Statement 2 are true, and Statement 2 provides a correct explanation for Statement 1, the correct option is: (a) Statement- 1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement-1