Question

part b: understanding concepts

1. fill in the table below with what happens to temperature, particle motion, and energy transfer when matter changes state.

change of state
solid -- liquid (melting)
liquid -- gas (evaporation)
gas -- liquid (condensation)
liquid -- solid (freezing)

1. explain why during a phase change the temperature may not increase even though heat is still being added.
2. in the simulation you can toggle show energy or show temperature (if available).

Explanation:

• Solid - Liquid (melting):
• Temperature Change: Remains constant (at melting point).
• Particle Motion Change: Particles gain enough energy to break some intermolecular forces, start to move more freely (less restricted than in solid).
• Energy Flow: Heat is added.
• Liquid - Gas (evaporation):
• Temperature Change: Can remain constant (at boiling point for full - scale boiling, or decrease for evaporation as it can occur at lower temperatures and is a cooling process).
• Particle Motion Change: Particles gain sufficient energy to overcome most intermolecular forces and move freely in all directions.
• Energy Flow: Heat is added.
• Gas - Liquid (condensation):
• Temperature Change: Remains constant (at condensation point).
• Particle Motion Change: Particles lose energy, move more slowly as intermolecular forces become stronger and restrict their motion more.
• Energy Flow: Heat is removed.
• Liquid - Solid (freezing):
• Temperature Change: Remains constant (at freezing point).
• Particle Motion Change: Particles lose energy, move less freely as they form a more ordered (solid) structure due to stronger intermolecular forces.
• Energy Flow: Heat is removed.

For the question of why during a phase change the temperature may not increase even though heat is still being added:

• During a phase change, the added heat energy is used to break or form intermolecular forces (for example, in melting, it is used to break the forces that hold particles in a solid lattice). This is called latent heat. The energy is not used to increase the kinetic energy of the particles (which is what causes a temperature increase in non - phase change heating).

Answer:

Change of State	Temperature Change	Particle Motion Change	Energy Flow (heat added or removed?)
Liquid - Gas (evaporation)	Constant (at boiling point) or decrease (for evaporation)	Particles move freely in all directions	Heat added
Gas - Liquid (condensation)	Constant (at condensation point)	Particles move more slowly (more restricted)	Heat removed
Liquid - Solid (freezing)	Constant (at freezing point)	Particles move less freely (form more ordered structure)	Heat removed

During a phase change, the added heat is used for latent heat (breaking/forming intermolecular forces), not for increasing particle kinetic energy (which causes temperature increase).