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Chapter 15: Problem 13

Normal butane and isobutane have boiling temperatures of -0.5 and \(-12.3^{\circ} \mathrm{C}(31.1\) and \(\left.9.9^{\circ} \mathrm{F}\right),\) respectively. Briefly explain this behavior on the basis of their molecular structures, as presented in Section 14.2.

Short Answer

Expert verified
Question: Explain the boiling temperature difference between normal butane and isobutane using their molecular structures. Answer: The difference in boiling points between normal butane and isobutane is due to the variations in their molecular structures, which influence the London dispersion forces acting between the molecules. Normal butane has a linear structure, allowing stronger intermolecular attraction and resulting in a higher boiling point. In contrast, isobutane has a branched structure that leads to weaker intermolecular attraction, resulting in a lower boiling point.

Step by step solution

01

Understand the molecular structure of normal butane and isobutane

Normal butane (C4H10) has a linear structure with a continuous carbon chain: H H H H | | | | H-C-C-C-C-H | | | | H H H H Isobutane (C4H10) has a branched structure with one of the carbons connected to three other carbons: H | H H-C-H | | H-C-C-H | | H H
02

Explain the effect of molecular structure on boiling point based on London dispersion forces

Boiling points are majorly influenced by the intermolecular forces between the molecules. In the case of normal butane and isobutane, the main force involved is the London dispersion force, which is a weak, temporary attractive force between the electron clouds of adjacent molecules.
03

Compare the molecular structures of normal butane and isobutane

While both normal butane and isobutane have the same molecular formula (C4H10), they have different molecular structures. The main difference between these structures is that normal butane has a linear structure, making it more elongated, while isobutane has a more compact, branched structure.
04

Relate the structures to their respective boiling points

In the normal butane molecule, since it has a longer and more elongated structure, the London dispersion forces can act more effectively over the larger surface area available. This makes the intermolecular attraction between normal butane molecules relatively strong, resulting in a higher boiling point. Conversely, isobutane's more compact and branched structure provides a less surface area for the London dispersion forces to act upon, leading to weaker intermolecular attraction between isobutane molecules. This results in a lower boiling point for isobutane.
05

Conclusion

The difference in boiling points between normal butane and isobutane can be attributed to the differences in their molecular structures, which affect the way London dispersion forces act between their molecules. Normal butane has a higher boiling point due to its linear structure, which allows stronger intermolecular attraction, while isobutane has a lower boiling point because of its branched structure that results in weaker intermolecular attraction.

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Most popular questions from this chapter

For each of the following pairs of polymers, do the following: (1) state whether or not it is possible to decide whether one polymer has a higher tensile strength than the other; (2) if this is possible, note which has the higher tensile strength and then cite the reason(s) for your choice; and (3) if it is not possible to decide, then state why. (a) Linear and isotactic poly(vinyl chloride) with a weight-average molecular weight of \(100,000 \mathrm{g} / \mathrm{mol} ;\) branched and atactic poly \((\) vinyl chloride) having a weight-average molecular weight of \(75,000 \mathrm{g} / \mathrm{mol}\) (b) Graft acrylonitrile-butadiene copolymer with \(10 \%\) of possible sites crosslinked; alternating acrylonitrile-butadiene copolymer with \(5 \%\) of possible sites crosslinked (c) Network polyester; lightly branched polytetrafluoroethylene

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