Why is the latent heat of vaporization higher than the latent heat of fusion of a substance?
The Correct Answer and Explanation is:
The latent heat of vaporization is higher than the latent heat of fusion for a substance because of the differences in the energy required to break intermolecular forces during phase transitions.
- Phase Transitions:
- Fusion (melting) occurs when a solid turns into a liquid. In this process, the substance’s particles (atoms, molecules, or ions) break some of the attractive forces holding them together in the solid state. However, in the liquid state, the particles still remain relatively close, and they can move around one another.
- Vaporization (boiling or evaporation) occurs when a liquid turns into a gas. This process requires more energy because it involves breaking almost all of the intermolecular forces, allowing the particles to spread out significantly and move freely in all directions.
- Energy Requirement:
- During fusion, the substance only needs enough energy to overcome the forces that maintain the structure of the solid. These forces are significant, but not as strong as those holding the particles in the liquid state. Therefore, the energy needed to convert a solid to a liquid is lower compared to vaporization.
- Vaporization requires more energy because it must break the relatively strong intermolecular forces between liquid molecules. In the liquid state, molecules are close enough to exert significant attraction, and overcoming these forces to turn the liquid into a gas requires significantly more energy.
- Distance Between Particles:
- In the solid phase, particles are packed in a fixed, orderly arrangement. In the liquid phase, particles are still relatively close, but they can move past each other. In the gas phase, particles are far apart, and the attraction between them is minimal. The transition from liquid to gas requires a complete separation of particles, which is energetically more demanding.
In summary, the latent heat of vaporization is higher than the latent heat of fusion because more energy is required to completely overcome the intermolecular forces during vaporization than during fusion.
