During a change of state, the energy of a substance is either absorbed or released as heat.
When a substance changes from one physical state (solid, liquid, gas) to another, its internal energy changes. This energy change doesn't result in a temperature change during the phase transition itself, but rather is used to overcome the forces holding the substance together in its original state or is released as the substance settles into a more ordered state.
Energy Absorption: Endothermic Processes
Processes that absorb energy from the surroundings are called endothermic. This energy input is needed to overcome the intermolecular forces holding the particles together, allowing them to move more freely.
- Melting: Changing from solid to liquid. Energy is absorbed to break down the rigid structure of the solid. As per the reference, during melting, energy is absorbed as heat.
- Vaporization (Boiling/Evaporation): Changing from liquid to gas. Energy is absorbed to overcome the liquid's intermolecular forces and allow particles to move independently as a gas.
- Sublimation: Changing directly from solid to gas. This requires significant energy absorption.
Energy Release: Exothermic Processes
Processes that release energy into the surroundings are called exothermic. This occurs as particles settle into a more ordered state, forming stronger intermolecular bonds or attractions, and excess energy is given off.
- Freezing: Changing from liquid to solid. Energy is released as particles arrange into a more ordered structure.
- Condensation: Changing from gas to liquid. Energy is released as gaseous particles come together and form weaker liquid bonds. As per the reference, during condensation, energy is released as heat.
- Deposition: Changing directly from gas to solid. This releases energy.
Summary of Energy Changes
Here's a quick look at how energy changes during common phase transitions:
| Change of State | Initial State | Final State | Energy Change | Process Type | Example Cited? |
|---|---|---|---|---|---|
| Melting | Solid | Liquid | Absorbed (as heat) | Endothermic | Yes |
| Freezing | Liquid | Solid | Released (as heat) | Exothermic | No |
| Vaporization/Boiling | Liquid | Gas | Absorbed (as heat) | Endothermic | No |
| Condensation | Gas | Liquid | Released (as heat) | Exothermic | Yes |
| Sublimation | Solid | Gas | Absorbed (as heat) | Endothermic | No |
| Deposition | Gas | Solid | Released (as heat) | Exothermic | No |
In essence, energy is a crucial component that facilitates the transition between states, either being taken in to increase the kinetic energy and overcome forces, or given out as particles settle into a lower energy configuration.
