Latent Heat and Kinetic Theory Phenomena

Latent Heat of Fusion and Vaporization  

Latent Heat of Fusion  

- The word latent means hidden or invisible.  

- When heat is applied to a solid (e.g., ice), it does not melt until the temperature reaches 0°C.  

- The heat supplied at this point is used for bond breaking rather than raising temperature.  

- Since this heat is not detectable by a thermometer, it is called latent heat of fusion.  

Latent Heat of Vaporization  

- Applies to liquids.  

- Water boils at 100°C, but the thermometer does not rise further even though heating continues.  

- The hidden heat is used to break intermolecular bonds, converting liquid into vapor.  

- This invisible energy is called latent heat of vaporization.  

Phenomena Supporting the Kinetic Theory of Matter  

The kinetic theory states that matter consists of tiny particles in continuous motion. Several natural phenomena support this idea:  

Brownian Motion  

- Discovered by Scottish botanist Robert Brown (1827).  

- Refers to the zig‑zag, haphazard movement of pollen grains observed under a microscope.  

- Later proven to be caused by continuous bombardment of pollen grains by mobile particles in the liquid.  

Diffusion  

- Occurs when particles in gases, liquids, or solids move from a region of high concentration to a region of low concentration.  

- Explains how substances naturally spread out to occupy available space.  

Osmosis  

- The movement of water molecules from a region of higher water concentration** to a region of lower water concentration.  

- Takes place through a semi‑permeable membrane.  

- Essential in biological processes such as nutrient absorption in plants.