Phase changes, such as melting, boiling, freezing, or condensation, are closely related to thermochemistry because they involve the absorption or release of heat without changing the chemical composition of a substance.
Key points:
- Energy transfer without temperature change:
- During a phase change, heat energy is absorbed or released, but the temperature remains constant until the change is complete.
- For example, when ice melts, it absorbs heat to break the bonds between water molecules, but the temperature stays at 0°C until all ice becomes water.
- Endothermic and exothermic processes:
- Melting and boiling are endothermic, meaning they absorb heat.
- Freezing and condensation are exothermic, meaning they release heat to the surroundings.
- Latent heat:
- The amount of heat involved in a phase change is called latent heat, which is a key concept in thermochemistry.
- It shows how energy is stored or released even without a temperature change.
- Real-world applications:
- Thermochemistry of phase changes is essential in designing refrigerators, air conditioners, steam engines, and even understanding weather patterns.
In short, phase changes demonstrate how heat energy can be absorbed or released without altering the chemical identity of a substance, which is a central idea in thermochemistry.