1. Solid to Liquid (Melting):
- The substance absorbs energy in the form of heat.
- The particles of the substance gain kinetic energy and begin to vibrate more vigorously.
- The attractive forces between the particles weaken, allowing them to move more freely.
- The substance changes from a rigid and well-defined shape (solid) to a fluid and non-rigid shape (liquid).
- The volume of the substance usually expands slightly due to increased molecular movement.
- The melting point is the specific temperature at which a substance changes from a solid to a liquid state.
2. Liquid to Gas (Vaporization):
- The substance continuously absorbs energy in the form of heat.
- The particles of the substance gain even more kinetic energy, increasing their speed and vibrational motion.
- The attractive forces between the particles become negligible, allowing them to move independently.
- The substance changes from a liquid with a definite volume to a gas that expands to fill its container.
- The volume of the substance increases significantly as the particles move further apart.
- The boiling point is the specific temperature at which a liquid changes into a gaseous state under a given pressure.
3. Gas to Liquid (Condensation):
- The substance loses energy in the form of heat to the surroundings.
- The gas particles slow down and lose kinetic energy, resulting in decreased molecular motion.
- Attractive forces between the particles become stronger, causing them to come closer together.
- The gas transforms into a liquid as the particles condense into a more compact form.
- The volume of the substance decreases significantly compared to its gaseous state.
- The condensation point is the temperature at which a gas converts into a liquid under a specific pressure.
4. Solid to Gas (Sublimation):
- This occurs when a solid directly transforms into a gas without passing through the liquid state.
- The solid particles absorb energy, gain kinetic energy, and overcome the attractive forces between them.
- Sublimation occurs at temperatures and pressures below a substance's triple point, where the three phases (solid, liquid, and gas) can coexist.
- Substances that sublime easily are called volatile, such as dry ice (solid carbon dioxide).
5. Liquid to Solid (Freezing):
- The reverse of melting, where a liquid loses energy in the form of heat to the surroundings.
- The liquid particles slow down, lose kinetic energy, and become more ordered.
- Attractive forces between the particles strengthen, causing them to form a rigid structure.
- The substance transitions from a liquid with a definite shape to a solid with a fixed shape and volume.
- The freezing point is the temperature at which a liquid transforms into a solid under specific pressure.
It's important to note that these phase changes can be influenced by factors such as temperature, pressure, and intermolecular forces within the substance. Different substances have different phase change temperatures, and some may undergo these transitions at different rates.
