Explain why C6H14 is liquid whereas C2H6 is a gas?
The Correct Answer and Explanation is:
The difference in the physical states of C6H14 (hexane) and C2H6 (ethane) at room temperature is primarily due to differences in molecular size, intermolecular forces, and boiling points.
Correct Answer:
C6H14 is a liquid at room temperature because it has a larger molecular structure, which leads to stronger van der Waals (dispersion) forces between the molecules. In contrast, C2H6 is a gas at room temperature because it is smaller and has weaker intermolecular forces.
Detailed Explanation:
- Molecular Size and Surface Area:
- C6H14 (hexane) is a larger molecule with six carbon atoms and fourteen hydrogen atoms. The greater size of hexane means it has a larger surface area for intermolecular interactions.
- C2H6 (ethane), on the other hand, is much smaller with only two carbon atoms and six hydrogen atoms. This small size results in a smaller surface area for intermolecular forces to act.
- Intermolecular Forces:
Both C6H14 and C2H6 are nonpolar molecules, and the primary type of intermolecular force between their molecules is London dispersion forces (a type of van der Waals force). These forces arise from temporary dipoles created as electrons move within molecules.
- In larger molecules like C6H14, the number of electrons is higher, leading to stronger temporary dipoles and thus stronger dispersion forces. These forces require more energy to overcome, which results in a higher boiling point and causes the substance to be a liquid at room temperature.
- In smaller molecules like C2H6, the dispersion forces are weaker due to fewer electrons and a smaller surface area for interaction. Consequently, less energy is needed to overcome these forces, and C2H6 remains a gas at room temperature.
- Boiling Points:
- The boiling point of C6H14 is around 68.7°C, which is significantly higher than the boiling point of C2H6, which is around -88.6°C. This difference indicates that C6H14 requires more heat to transition from liquid to gas, making it a liquid at standard conditions.
In summary, the larger molecular size of C6H14 leads to stronger intermolecular forces, causing it to be a liquid, while the smaller size and weaker intermolecular forces of C2H6 cause it to remain a gas at room temperature.