The letent heat of vaporisation of a substance is always

Options

A. greater than its latents heat of fusions
B. greater than its latent heat of sublimation
C. equal to its latent heat of sublimation
D. less than its latent heat of fusion

Answer

To solve the question regarding the latent heat of vaporization of a substance, we will follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Latent Heat**:
- Latent heat is the heat energy required to change the phase of a substance without changing its temperature. There are different types of latent heat, including latent heat of fusion (solid to liquid) and latent heat of vaporization (liquid to gas).

2. **Identify the Phases**:
- Consider water as an example. At 0°C, ice (solid) can be converted to water (liquid) at the same temperature, which requires latent heat of fusion.
- At 100°C, water (liquid) can be converted to steam (gas) at the same temperature, which requires latent heat of vaporization.

3. **Compare the Energy Required**:
- The latent heat of vaporization involves breaking the intermolecular forces between water molecules to convert them into vapor. This requires more energy compared to the latent heat of fusion, which only needs to overcome the forces holding the molecules in a solid structure.

4. **Conclusion**:
- Since the energy required to convert a liquid to a gas (latent heat of vaporization) is greater than that required to convert a solid to a liquid (latent heat of fusion), we conclude that:
\[ \text{Latent heat of vaporization} > \text{Latent heat of fusion} \]

5. **Final Answer**:
- Therefore, the correct answer to the question is that the latent heat of vaporization of a substance is always greater than its latent heat of fusion.