Explain in terms of particles what happens when methane boils and why the boiling point of methane is lower than that of butane.
The Correct Answer and Explanation is:
When methane (CH₄) boils, the process involves the transition of methane molecules from the liquid phase to the gas phase. In the liquid state, methane molecules are held together by weak intermolecular forces, primarily London dispersion forces. These forces are the result of temporary fluctuations in electron density that create momentary dipoles, which induce similar dipoles in neighboring molecules. As heat is applied, the kinetic energy of the methane molecules increases. Once the molecules acquire enough energy to overcome the weak London dispersion forces between them, they escape into the air as a gas. This process is known as boiling.
The boiling point of a substance depends on the strength of the intermolecular forces between its molecules. In the case of methane, these London dispersion forces are relatively weak due to the small size and low mass of methane molecules. Methane’s boiling point is −161.5°C, which is very low because the forces holding the molecules together are not strong enough to require much energy to break.
In contrast, butane (C₄H₁₀) has a higher boiling point of −0.5°C. This is because butane molecules are larger and more complex than methane molecules, with more electrons and a larger surface area. Larger molecules have stronger London dispersion forces because the temporary dipoles generated are stronger and can interact more significantly with neighboring molecules. As a result, more energy is required to overcome the intermolecular forces and transition butane from liquid to gas. This higher energy requirement results in a higher boiling point for butane compared to methane.
In summary, methane boils at a lower temperature than butane because the weak intermolecular forces in methane require less energy to overcome, while butane’s larger, more complex molecules experience stronger forces, leading to a higher boiling point.