Question

(solids, liquids, gases)
most substances go through a phase change when heated or cooled. molecules/atoms of a substance are held together in either the solid, liquid, or gas phase by attractive forces and these forces are affected by the addition or removal of heat.
model 1: representations of molecules in three phases

1. the phase change represented by the arrow labeled d is ______________
2. the phase change represented by the arrow labeled e is ______________
3. the phase change represented by the arrow labeled f is ______________
4. the phase change represented by the arrow labeled g is ______________
5. which arrows indicate the addition of heat?
6. how do you know that these phase changes require heat to be added?
7. which arrows indicate the removal of heat?
8. how do you know that these phase changes require removal of heat?

Explanation:

Step1: Identify phase changes

• Arrow D: From liquid (B) to solid (A). This is freezing.
• Arrow E: From solid (A) to liquid (B). This is melting.
• Arrow F: From liquid (B) to gas (C). This is vaporization.
• Arrow G: From gas (C) to liquid (B). This is condensation.

Step2: Determine heat addition/removal

• Heat addition: Melting (E) and vaporization (F). As temperature increases from solid to liquid (E: \(0^{\circ}C\) to \(0 - 100^{\circ}C\)) and from liquid to gas (F: \(0 - 100^{\circ}C\) to \(100^{\circ}C\)), heat is added to overcome attractive forces between molecules.
• Heat removal: Freezing (D) and condensation (G). As temperature decreases (D: \(0 - 100^{\circ}C\) to \(0^{\circ}C\); G: \(100^{\circ}C\) to \(0 - 100^{\circ}C\)), heat is removed and attractive forces become more dominant.

Answer:

1. Freezing
2. Melting
3. Vaporization
4. Condensation
5. E and F
6. Temperature increases (from solid to liquid for E: \(0^{\circ}C\) to \(0 - 100^{\circ}C\); from liquid to gas for F: \(0 - 100^{\circ}C\) to \(100^{\circ}C\)) and heat is needed to break molecular - level attractive forces.
7. D and G
8. Temperature decreases (D: \(0 - 100^{\circ}C\) to \(0^{\circ}C\); G: \(100^{\circ}C\) to \(0 - 100^{\circ}C\)) and heat is released as molecular - level attractive forces become more significant.