Why does acetic acid have a higher boiling point than 1-bromoethane if the molar mass for 1-bromoethane is higher?
I think so
Acetic acid has hydrogen bonding. Bromoethane does not have H bonding.
Acetic acid (CH3COOH) has a higher boiling point than 1-bromoethane (C2H5Br) despite having a lower molar mass. This is because boiling points are not solely dependent on molar mass but also influenced by the intermolecular forces present in a compound.
Intermolecular forces are the attractive forces between molecules that determine their physical properties. Acetic acid contains hydrogen bonding, which is a particularly strong intermolecular force. Hydrogen bonding occurs when the hydrogen atom in one molecule is attracted to a more electronegative atom in another molecule, such as oxygen or nitrogen.
1-bromoethane, on the other hand, does not exhibit hydrogen bonding. It has weaker intermolecular forces, such as dipole-dipole interactions and London dispersion forces. These forces are weaker than hydrogen bonding and do not require highly polar or charged atoms.
Due to the presence of hydrogen bonding in acetic acid, more energy is required to break these stronger intermolecular forces compared to the forces present in 1-bromoethane. Thus, acetic acid has a higher boiling point despite having a lower molar mass.
The boiling point of a substance depends on various factors including intermolecular forces, molecular size, and molecular shape. In this case, acetic acid (CH3COOH) has a higher boiling point compared to 1-bromoethane (CH3CH2CH2Br) even though its molar mass is lower.
To understand this, we need to look at the intermolecular forces present in each compound. Acetic acid is capable of forming strong hydrogen bonds, which are attractive forces between the slightly positive hydrogen atom in one molecule and the slightly negative oxygen atom in another molecule. These hydrogen bonds are stronger than the intermolecular forces present in 1-bromoethane, which are primarily London dispersion forces.
Hydrogen bonds are generally stronger than London dispersion forces because they involve the attraction between a positively charged hydrogen atom and an electronegative atom (such as oxygen or nitrogen) in another molecule. In the case of acetic acid, the hydrogen bonds between adjacent molecules are more significant than the London dispersion forces holding 1-bromoethane molecules together.
These stronger hydrogen bonds require more energy to break, which leads to a higher boiling point for acetic acid compared to 1-bromoethane. Therefore, even though the molar mass of 1-bromoethane is higher, the presence of stronger intermolecular forces (hydrogen bonding) in acetic acid results in a higher boiling point.
In summary, the boiling point of a substance is not solely determined by its molar mass, but also by the types and strengths of the intermolecular forces present.