. Both neopentane and n-pentane have a C5H12 formula. a. Which compound has a higher boiling point? b. Which compound has stronger London forces? c. What conclusion can be drawn about straight chain and branched chain hydrocarbons from this example?
Please help answer question 4 and 5
The Correct Answer and Explanation is:
4.
a. n-Pentane has a higher boiling point than neopentane.
b. n-Pentane has stronger London dispersion forces than neopentane.
5. Explanation
Although n-pentane and neopentane have the same molecular formula (C₅H₁₂), their structures differ significantly. n-Pentane is a straight-chain hydrocarbon, while neopentane (also called 2,2-dimethylpropane) is a highly branched isomer.
The boiling point of a substance is influenced by the strength of intermolecular forces between its molecules. The dominant intermolecular forces in alkanes like n-pentane and neopentane are London dispersion forces, which are weak but increase with molecular surface area and molecular contact.
n-Pentane has a more extended, linear shape that allows its molecules to come into closer contact with each other. This results in more surface area for intermolecular interactions, leading to stronger London dispersion forces. In contrast, neopentane is compact and spherical in shape. This reduces the surface area available for molecular interactions, resulting in weaker London forces.
As a result of these differences:
- n-Pentane has a higher boiling point (approximately 36 °C) than neopentane (approximately 9.5 °C).
- n-Pentane also exhibits stronger London dispersion forces because its molecules can interact more extensively.
Conclusion:
From this comparison, we can conclude that straight-chain hydrocarbons generally have higher boiling points and stronger intermolecular forces than their branched-chain isomers. This is due to the greater surface area that allows for more effective intermolecular contact in straight-chain molecules. Branched-chain hydrocarbons, being more compact, have reduced surface interactions and thus lower boiling points.
This principle is important in physical chemistry and organic chemistry, as it helps explain trends in physical properties like boiling and melting points across isomers and is relevant in applications such as fuel formulation and separation processes
