Which of the following has the highest heat of vaporization ?

Options

A. HF
B. HCl
C. HBr
D. Hl

Answer

To determine which of the following substances has the highest heat of vaporization among HF, HCl, HBr, and HI, we need to analyze the intermolecular forces present in each substance.

### Step-by-Step Solution:

1. **Understanding Heat of Vaporization**:
- Heat of vaporization is the amount of energy required to convert a liquid into a gas at constant temperature and pressure. It is influenced by the strength of intermolecular forces present in the liquid.

2. **Identifying Intermolecular Forces**:
- The primary intermolecular forces to consider are hydrogen bonding, dipole-dipole interactions, and London dispersion forces.
- HF (hydrogen fluoride) exhibits strong hydrogen bonding due to the highly electronegative fluorine atom, which creates a significant dipole.

3. **Comparing the Substances**:
- **HF**: Strong hydrogen bonding due to the presence of fluorine.
- **HCl**: Weaker dipole-dipole interactions compared to HF.
- **HBr**: Even weaker dipole-dipole interactions than HCl.
- **HI**: Weakest interactions among the four, primarily London dispersion forces.

4. **Conclusion**:
- Since HF has strong hydrogen bonds, it requires more energy to break these bonds compared to the other molecules, which have weaker intermolecular forces. Therefore, HF will have the highest heat of vaporization.

5. **Final Answer**:
- The substance with the highest heat of vaporization is **HF**.