Although water and ammonia differ in molar mass by only one unit, the boiling point of water is over 100 degrees C higher than that of ammonia. What forces in liquid water that do not exist in liquid ammonia could account for this observation?
I think the major difference is the electronegativity of N versus that of O. Both NH3 and H2O have hydrogen bonding but the strength of that bond is more in H2O than in NH3. That may not answer your question since the questions asks for DIFFERENT forces present in water and not present in NH3. I wonder what the surface tension is for NH3 and could that account for over 100 C
they both have hydrogen bonding yet; H20 has a stronger Hydrogen bonding ;)
The difference in boiling points between water and ammonia can be attributed to the intermolecular forces present in each liquid. In water, the main intermolecular forces are hydrogen bonding, whereas ammonia primarily exhibits weaker dipole-dipole interactions.
1. Hydrogen Bonding in Water: Water molecules can form hydrogen bonds due to the presence of hydrogen atoms bonded to highly electronegative oxygen atoms. These hydrogen bonds are stronger than typical dipole-dipole interactions. The hydrogen bonding results in a more extensive network of intermolecular attractions in water, leading to higher boiling points. These bonds make it more difficult for water molecules to separate from one another and transition into the gas phase.
2. Dipole-Dipole Interactions in Ammonia: Ammonia molecules possess a polar covalent bond, with the more electronegative nitrogen atom exerting a stronger pull on the shared electrons. This molecular polarity leads to dipole-dipole interactions between ammonia molecules. However, these interactions are relatively weaker compared to hydrogen bonding in water. Consequently, ammonia has a lower boiling point due to the ease with which its molecules can overcome the intermolecular forces and transition into the gas phase.
In summary, the presence of hydrogen bonding in water, absent in ammonia, accounts for the significant difference in boiling points between the two substances.
The difference in boiling points between water and ammonia can be attributed to the presence of hydrogen bonding in water, which is absent in ammonia. Hydrogen bonding is a special type of intermolecular force that occurs when a hydrogen atom is bonded to an electronegative atom (such as oxygen in water).
To explain this phenomenon, we can look at the intermolecular forces present in both substances. In liquid water, the water molecules are held together by hydrogen bonds. These bonds are significantly stronger than the intermolecular forces in liquid ammonia, which are primarily London dispersion forces or Van der Waals forces.
Hydrogen bonding is a result of the large difference in electronegativity between hydrogen and oxygen atoms. Oxygen is more electronegative, meaning it has a greater affinity for electrons. As a result, the oxygen atom in one water molecule attracts the hydrogen atoms of neighboring water molecules, creating a strong dipole-dipole interaction. This hydrogen bonding gives water its unique properties such as a high boiling point, unusually high surface tension, and heat capacity.
In contrast, ammonia molecules lack a highly electronegative atom like oxygen to form hydrogen bonds. The intermolecular forces between ammonia molecules are primarily London dispersion forces, which occur due to temporary partial charges that arise from the constant fluctuation of electrons. London dispersion forces are weaker than hydrogen bonds, resulting in a lower boiling point for ammonia compared to water.
Therefore, the absence of hydrogen bonding in liquid ammonia and the presence of hydrogen bonding in liquid water can account for the significant difference in their boiling points, with water having a boiling point more than 100 degrees Celsius higher than that of ammonia.