Energy of Phase Changes and Phase Diagrams
When substances change phase, energy is either absorbed or released while the temperature remains constant. Endothermic phase changes (solid→liquid and liquid→gas) absorb energy, while exothermic phase changes (liquid→solid and gas→liquid) release energy. The energy absorbed in one direction equals the energy released in the reverse direction.
Phase diagrams show how substances exist at different temperatures and pressures. The triple point represents where a substance can exist simultaneously in all three phases. The critical point marks the highest combination of temperature and pressure at which a substance can exist between gas and liquid states.
Special phase transitions include sublimation (solid directly to gas) and deposition (gas directly to solid). These transitions bypass the liquid phase entirely and can be seen in everyday examples like dry ice.
Did you know? While most substances expand when melting, water is unique - it actually expands when freezing, which is why ice floats!
