Lena Savoie
The boiling point of a substance is influenced by its molecular structure and the presence of intermolecular forces. Hexane (C6H14) and methyl alcohol (or methanol) have different molecular structures and exhibit varying strengths of intermolecular forces, which lead to a difference in their boiling points. Hexane has a linear structure composed of carbon and hydrogen atoms, while methanol has a smaller yet more complex structure due to the presence of the polar hydroxyl group. This difference in molecular structure and polarity results in distinct intermolecular forces, with hexane exhibiting weaker London dispersion forces (or van der Waals forces) compared to the stronger hydrogen bonding in methanol. As a result, methanol has a higher boiling point than hexane.
| Characteristics | Values |
|---|---|
| Boiling point of hexane | 68.0 °C |
| Boiling point of methyl alcohol | 64.7 °C |
| Molecular structure of hexane | Larger molecule with a simple linear structure composed of carbon and hydrogen atoms |
| Molecular structure of methyl alcohol | Smaller molecule with a more complex structure due to the presence of the polar hydroxyl group |
| Intermolecular forces in hexane | London dispersion forces (van der Waals forces) |
| Intermolecular forces in methyl alcohol | Hydrogen bonding and London dispersion forces |
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What You'll Learn
Boiling point of hexane vs methyl alcohol
The boiling point of a substance is the temperature at which its vapour pressure equals the atmospheric pressure. It reflects the amount of energy needed to overcome intermolecular forces and allow molecules to escape from the liquid phase into the gaseous phase.
The normal boiling point of methyl alcohol is 64.7 °C. On the other hand, the normal boiling point of hexane is 68.0 °C. Ordinarily, we would assume that the smaller hydrocarbon would be more volatile. However, this is not the case in this situation.
Hexane is a nonpolar molecule composed of only carbon and hydrogen atoms, bonded together by nonpolar covalent bonds. The molecule is larger with a relatively simple linear structure. The only intermolecular force present in hexane is London dispersion forces (van der Waals forces), which are relatively weak. These forces arise from temporary fluctuations in electron density, leading to induced dipoles in neighbouring hexane molecules.
Methanol, on the other hand, is a polar molecule with a hydroxyl (-OH) group. It exhibits hydrogen bonding in addition to London dispersion forces. Hydrogen bonding is a stronger intermolecular force compared to London dispersion forces. The presence of hydrogen bonds in methanol leads to stronger intermolecular attractions, increasing its boiling point. The hydroxyl group in methanol is more exposed, allowing it to hydrogen bond more easily with its neighbouring molecules. This results in stronger attractions between methanol molecules, requiring more energy to break these interactions and thus resulting in a higher boiling point compared to hexane.
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Intermolecular forces
The boiling point of a substance is the temperature at which its vapour pressure equals the atmospheric pressure. It reflects the amount of energy required to overcome intermolecular forces and allow molecules to escape from the liquid phase into the gaseous phase.
The difference in the boiling points of hexane and methyl alcohol (methanol) can be attributed to the presence of hydrogen bonding and the polar nature of methyl alcohol molecules, leading to stronger intermolecular forces of attraction between methyl alcohol molecules.
Hexane is a nonpolar molecule composed of only carbon and hydrogen atoms, bonded together by nonpolar covalent bonds. The molecule has a relatively simple linear structure. The only intermolecular force present in hexane is London dispersion forces (van der Waals forces), which are relatively weak and arise from temporary fluctuations in electron density, leading to induced dipoles in neighbouring hexane molecules.
On the other hand, methyl alcohol is a polar molecule with a hydroxyl (-OH) group. It exhibits hydrogen bonding in addition to London dispersion forces. Hydrogen bonding is a stronger intermolecular force compared to London dispersion forces. The presence of hydrogen bonds in methyl alcohol leads to stronger intermolecular attractions, increasing its boiling point. Methyl alcohol molecules can pack more closely together due to hydrogen bonding, resulting in stronger intermolecular attractions. This also means that more energy is required to break these interactions, resulting in a higher boiling point compared to hexane.
In summary, the difference in the boiling points of hexane and methyl alcohol can be attributed to the different types of intermolecular forces present in each substance.
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Molecular structure
The boiling point of a substance is the temperature at which its vapour pressure equals the atmospheric pressure. It depends on the molecular structure of the substance and the intermolecular forces between the molecules.
Hexane (C6H14) is a nonpolar molecule composed of carbon and hydrogen atoms bonded together by nonpolar covalent bonds. It has a simple linear structure. The only intermolecular force present in hexane is the London dispersion force (van der Waals force), which is relatively weak. These forces arise from temporary fluctuations in electron density, leading to induced dipoles in neighbouring hexane molecules.
On the other hand, methanol (methyl alcohol) is a polar molecule with a hydroxyl (-OH) group. It has a more complex structure than hexane due to the presence of this polar group. The hydroxyl group allows methanol to exhibit hydrogen bonding, a stronger type of intermolecular force compared to London dispersion forces.
The presence of hydrogen bonding in methanol results in stronger attractions between methanol molecules. This leads to a higher boiling point compared to hexane. More energy is required to break these strong hydrogen bonds in methanol, allowing it to remain in the liquid phase at higher temperatures.
The difference in molecular size and complexity between hexane and methanol also influences the strength of their intermolecular forces. Methanol molecules, despite being smaller, can pack more closely together due to hydrogen bonding. This results in stronger intermolecular attractions and contributes to methanol's higher boiling point.
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Hydrogen bonding
The boiling point of a substance is the temperature at which its vapour pressure equals the atmospheric pressure. It reflects the amount of energy required to overcome intermolecular forces and allow molecules to escape from the liquid phase into the gaseous phase.
Hexane and methyl alcohol (methanol) differ in their intermolecular forces and molecular structures, which leads to a difference in their boiling points. Hexane is a nonpolar molecule composed of carbon and hydrogen atoms bonded by nonpolar covalent bonds. The only intermolecular force present in hexane is the relatively weak London dispersion force (van der Waals force). On the other hand, methanol is a polar molecule with a hydroxyl (-OH) group, which exhibits hydrogen bonding in addition to London dispersion forces.
The difference in molecular size and complexity between hexane and methanol also influences the strength of their intermolecular forces. Despite having a smaller molar mass, methanol molecules can pack more closely together due to hydrogen bonding, resulting in a higher boiling point compared to hexane.
In summary, the higher boiling point of methanol compared to hexane can be attributed to the presence of hydrogen bonding, which leads to stronger intermolecular forces of attraction between methanol molecules.
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Van Der Waals forces
The boiling point of a substance is the temperature at which its vapour pressure equals the atmospheric pressure. It indicates the amount of energy required to overcome intermolecular forces and enable molecules to transition from the liquid phase to the gaseous phase.
Hexane has a higher boiling point than methanol due to differences in intermolecular forces and molecular structure. The higher boiling point of methanol can be attributed to the presence of hydrogen bonding and the polar nature of methanol molecules, leading to stronger intermolecular forces of attraction between methanol molecules.
Hexane is a nonpolar molecule composed of only carbon and hydrogen atoms bonded by nonpolar covalent bonds. The only intermolecular force present in hexane is Van Der Waals forces, also known as London dispersion forces, which arise from temporary fluctuations in electron density. These forces are relatively weak and can be easily overcome with a relatively low amount of energy, resulting in a lower boiling point for hexane.
On the other hand, methanol, being a polar molecule with a hydroxyl (-OH) group, exhibits hydrogen bonding in addition to Van Der Waals forces. Hydrogen bonding is a stronger intermolecular force compared to London dispersion forces. The presence of hydrogen bonds in methanol results in stronger intermolecular attractions, requiring more energy to break these interactions, which leads to a higher boiling point.
The difference in molecular size and complexity between hexane and methanol also influences the strength of their intermolecular forces. Methanol molecules, despite being smaller, can pack more closely together due to hydrogen bonding, resulting in stronger intermolecular attractions and a higher boiling point.
In summary, the higher boiling point of methanol compared to hexane is primarily due to the presence of hydrogen bonding in methanol, which results in stronger intermolecular forces of attraction. Hexane, being a nonpolar molecule, exhibits only the weaker Van Der Waals forces, which require less energy to break, resulting in a lower boiling point.
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Frequently asked questions
The normal boiling point of n-hexane is 68.0 °C, whereas the boiling point of methyl alcohol is 64.7 °C.
Hexane is a nonpolar molecule composed of carbon and hydrogen atoms, with weak London dispersion forces (also known as van der Waals forces) as the predominant intermolecular force. On the other hand, methyl alcohol (methanol) is a polar molecule with a hydroxyl (-OH) group, allowing it to exhibit stronger intermolecular forces through hydrogen bonding. The presence of hydrogen bonding in methanol results in stronger attractions between its molecules, requiring more energy to break these interactions and thus leading to a higher boiling point compared to hexane.
Although hexane is a larger molecule, methyl alcohol's smaller size and complex structure due to the presence of the polar hydroxyl group allow its molecules to pack more closely together through hydrogen bonding. This results in stronger intermolecular attractions, contributing to its higher boiling point.
The difference in boiling points between hexane and methyl alcohol is primarily due to the varying strengths of intermolecular forces present in each substance. The boiling point of a substance reflects the amount of energy required to overcome these intermolecular forces and transition from a liquid to a gas phase. Understanding these differences can provide insights into the behaviour of substances under different conditions and is essential in fields such as chemistry and materials science.
