Question

The false statement among the following is (1) Bond energy of covalent \(0-H\) bond in water is greater than bond energy of hydrogen bond. (2) The intermolecular attractive forces vary in the order: water \(>\) ether \(>\) alcohol. (3) The high heat of vapourisation of water is due to hydrogen bonding. (4) Acetic acid exists as a dimer in benzene due to hydrogen bonding.

Short answer

The false statement is (2), as alcohol typically has stronger intermolecular forces than ether.

Step-by-step solution

- Understanding bond energies

Compare the bond energy of covalent bonds and hydrogen bonds. The bond energy of the covalent O-H bond in water is quite high compared to hydrogen bonds. Determine if option (1) is true.

- Intermolecular attractive forces

Examine the intermolecular forces between different molecules. Water has strong hydrogen bonds, ethers have weaker dipole-dipole interactions, and alcohols have hydrogen bonding but weaker than water. Evaluate if option (2) is accurate.

- Evaluate high heat of vaporization

Assess whether the high heat of vaporization of water is attributable to hydrogen bonding. Validate option (3) based on this property.

- Acetic acid dimer formation

Analyze the behavior of acetic acid in non-polar solvents like benzene. Hydrogen bonding can cause acetic acid to form dimers. Check if option (4) holds true.

- Identifying the false statement

Based on the analysis of the previous steps, identify which statement is incorrect.

Key concepts

bond energy

Bond energy refers to the amount of energy required to break one mole of bonds in a molecule, separating it into individual atoms. The bond energy of the covalent O-H bond in water is considerably high. This energy is much greater than the energy involved in breaking a hydrogen bond. In general, covalent bonds, like the O-H bond, are much stronger than hydrogen bonds. For instance, the bond energy of the O-H bond in water is about 463 kJ/mol, whereas hydrogen bonds are typically weaker, with bond energies around 20 kJ/mol. Understanding the difference in bond energies is critical in comparing the strength and stability of different types of bonds.

hydrogen bonding

Hydrogen bonding is a special type of intermolecular force that occurs when a hydrogen atom, which is covalently bonded to an electronegative atom like oxygen, nitrogen, or fluorine, interacts with another electronegative atom. This bond is relatively strong compared to other intermolecular forces such as Van der Waals forces but is weaker than covalent bonds. Hydrogen bonds are responsible for many of the unique properties of water, such as its high boiling point and heat of vaporization. Water molecules, thanks to hydrogen bonding, exhibit significant cohesion and surface tension, which impacts various biological and chemical processes.

intermolecular forces

Intermolecular forces are forces of attraction or repulsion between molecules. Different types of intermolecular forces include:

• **Van der Waals forces**: Weak attractive forces that occur due to temporary dipoles induced in atoms or molecules.
• **Dipole-dipole interactions**: Present between molecules with permanent dipole moments. Ether molecules, for example, exhibit these forces.
• **Hydrogen bonding**: This occurs in molecules like water and alcohols where hydrogen is covalently bonded to electronegative atoms.

These forces play a crucial role in determining the physical properties of substances, such as their boiling and melting points. For example, in the given exercise, water exhibits stronger hydrogen bonding compared to ether and alcohol, resulting in it having higher boiling and melting points.

heat of vaporization

Heat of vaporization is the amount of energy needed to convert one mole of a liquid into a gas at its boiling point. This value is notably high for water due to hydrogen bonding. Because water molecules form extensive hydrogen bonds, a large amount of energy is needed to break these bonds during vaporization. For water, the heat of vaporization is 40.79 kJ/mol at 100°C. This high value has significant implications for temperature regulation and energy transfer in natural and biological systems. It also explains why sweat, which is mainly water, is effective in cooling the body as it evaporates.