1. Melting (Solid to Liquid):
* Energy Input: Heat energy is absorbed by the ice, causing the molecules to vibrate faster.
* Molecular Change: The bonds holding the ice molecules in a rigid, crystalline structure weaken and break. The molecules gain enough energy to move around more freely, resulting in a liquid state.
* Temperature: The temperature remains at 0°C (32°F) during the melting process, as all the energy is used to break the bonds.
2. Boiling/Evaporation (Liquid to Vapor):
* Energy Input: More heat energy is absorbed by the liquid water.
* Molecular Change: Water molecules gain even more kinetic energy and break free from the surface of the liquid. They enter the gaseous phase, forming water vapor.
* Temperature: The temperature remains at 100°C (212°F) during boiling at standard atmospheric pressure, as the energy is used to overcome the forces holding the molecules together in the liquid state. Evaporation can occur at temperatures below boiling, but the rate is slower.
Key Points:
* Phase Change: These processes are phase changes, where the state of matter changes but the chemical composition (H₂O) remains the same.
* Energy Transfer: Both melting and boiling require energy input to break the bonds holding the molecules together.
* Reversibility: These processes are reversible: vapor can condense to liquid, and liquid can freeze to solid.
Let me know if you want more details about any of these stages!
