Given below are two statements:
Statement I : The boiling point of three isomeric pentanes follows the order
n-pentane > isopentane > neopentane
Statement II : When branching increases, the molecule attains a shape of sphere. This results in smaller surface area for contact, due to which the intermolecular forces between the spherical molecules are weak, thereby lowering the boiling point.
In the light of the above statements, choose the most appropriate answer from the options given below:
- ABoth Statement I and Statement II are correct
- BBoth Statement I and Statement II are incorrect
- CStatement I is correct but Statement II is incorrect
- DStatement I is incorrect but Statement II is correct
View written solutionFree
Correct answer: A
The two statements provided deal with molecular structure and boiling points of isomers of pentane. Let's analyze both statements:
Statement I: This statement lists the boiling point order of the three isomers of pentane as n-pentane > isopentane > neopentane. To verify this statement, let's consider the molecular structure and boiling points of each isomer:
- n-pentane: It is a straight-chain alkane with the formula $C_5H_{12}$, and it has the highest boiling point among the isomers because of its larger surface area which allows for greater van der Waals forces (dispersion forces).
- isopentane (also known as methylbutane): It has one branch in its carbon chain. The branching reduces the surface area slightly, which slightly weakens the van der Waals forces compared to n-pentane.
- neopentane (also known as dimethylpropane): It has a highly branched structure making it almost spherical. This shape minimizes the surface area significantly, thereby reducing the van der Waals forces drastically compared to the other two isomers.
Thus, the boiling point order correctly reflects the influence of molecular structure and intermolecular forces. Hence, Statement I is correct.
Statement II: This statement elaborates on why branching leads to lower boiling points. The assertion is that increased branching gives the molecule a more spherical shape, which then results in a smaller surface area, and thus weaker intermolecular forces (primarily van der Waals forces). Weaker intermolecular forces correspond with a lower energy requirement for the liquid to gas phase transition, thereby lowering the boiling point. This explanation is coherent with concepts in physical chemistry regarding molecular interactions and phase change. Therefore, Statement II is also correct.
In summary, both Statement I and Statement II are correct, reflecting the accurate relationship between molecular structure, intermolecular forces, and physical properties like boiling points. Therefore, the correct answer is:
Option A: Both Statement I and Statement II are correct.
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