Question
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:
Options
Solution
Sol. [Key Concept: Branching and boiling point of alkanes]
Both statements are correct. The approximate boiling points are n-pentane 309 K, isopentane 301 K and neopentane 282.5 K. Increased branching makes these isomers more compact and reduces effective intermolecular contact, weakening London dispersion attractions. Their boiling points therefore decrease in the stated order. Hence, option (3).
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