An energy transfer does not always result in a phase change because the energy added or removed can go into changing the temperature or kinetic energy of the substance's particles rather than overcoming the potential energy barriers needed for a phase change. Phase changes specifically require energy to break or form the bonds between particles, which is called latent heat, and during this process, the temperature remains constant. If the energy transfer is not sufficient to break these bonds or if it is transferred as sensible heat (increasing particle kinetic energy), the phase of the substance does not change.
Explanation of Phase Change and Energy Transfer
- When energy is transferred to a substance, it can either increase the particles' kinetic energy (raising temperature) or be used to alter the potential energy to change the phase (solid, liquid, gas).
- During a phase change, added energy (latent heat) is used to overcome intermolecular forces to transition between phases, without changing temperature.
- If the energy transfer is less than required latent heat, or if it raises the temperature within a phase range, no phase change occurs.
Latent Heat vs. Sensible Heat
- Latent heat is energy absorbed or released during phase change without temperature change.
- Sensible heat is energy that changes the temperature but not the phase.
- Before a phase change can occur, the substance must reach a specific temperature (phase change point) where latent heat can then act to change phases.
Summary
Energy transfer alone is not enough for a phase change; the type and amount of energy, and whether it is used to break intermolecular bonds or increase temperature, determine if a phase change occurs. Only when enough energy is provided as latent heat at a phase change temperature will the substance change its phase. These concepts are supported by the explanations on phase changes and latent heat from physics and chemistry sources.
