Phase Changes: Particle Behavior and Energy Transfer
What Happens to Particles During Phase Changes?
- During a phase change, a substance transitions between solid, liquid, and gas states.
- These changes occur at a constant temperature, where energy is used to alter the arrangement of particles rather than their speed.
Temperature measures the average kinetic energy of particles, while phase changes involve changes in potential energy.
Melting and Freezing
- Melting occurs when a solid becomes a liquid.
- As energy is added, particles vibrate more vigorously until they overcome the forces holding them in fixed positions.
- Conversely, freezing is the process where a liquid becomes a solid.
- Energy is removed, causing particles to slow down and settle into a structured arrangement.
- When ice melts, the temperature remains at 0°C until all the ice has turned into water.
- During this time, the energy added increases the potential energy of the particles, not their kinetic energy.
Boiling and Condensation
- Boiling is the transition from liquid to gas.
- At the boiling point, energy is used to break the intermolecular forces, allowing particles to move freely.
- Condensation is the reverse process, where gas particles lose energy and form a liquid.
Boiling occurs throughout the liquid at a specific temperature, while evaporation happens only at the surface and can occur at any temperature.
Evaporation
- Evaporation is a surface phenomenon where the fastest-moving particles escape into the gas phase.
- This process cools the remaining liquid because the average kinetic energy of the particles decreases.
- Evaporation is why sweating cools you down.
- As sweat evaporates, it absorbs energy from your skin, reducing your body temperature.
Quantitative Analysis of Heat Transfer
Specific Heat Capacity
Definition
Specific heat capacity
The specific heat capacity $c$ of a substance is the energy required to raise the temperature of 1 kg of the substance by 1 K.
The formula for calculating the energy transferred is:
$$Q = mc\Delta T$$
