Educational worksheet on states of matter and phase changes, illustrating solid, liquid, and gas with molecular diagrams and phase change examples.

Let's go through the worksheet and solve each phase change problem, explaining the reasoning behind each answer. The goal is to identify the phase change occurring and whether energy is increasing or decreasing.

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🔹 Background: States of Matter & Phase Changes

- Solid: Particles are tightly packed, fixed shape and volume.
- Liquid: Particles are close but can move; takes container shape, definite volume.
- Gas: Particles are far apart, high motion, no fixed shape or volume.

Phase changes involve energy transfer:
- Adding energy → particles gain kinetic energy → phase changes like melting, vaporization, sublimation.
- Removing energy → particles lose kinetic energy → phase changes like freezing, condensation, deposition.

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✔ Problem 1:

Left image: Particles are loosely packed (liquid state).
Right image: Particles are tightly packed in a regular pattern (solid state).

➡️ This is a change from liquid to solid.

🔹 Phase Change: Freezing
🔹 Energy: Decrease — Energy is removed to form a solid.

✔ Answer:
- Phase Change: Freezing
- Energy: decrease

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✔ Problem 2:

Left image: Particles are widely spaced and moving freely (gas state).
Right image: Particles are closer together, still fluid but not as spread out (liquid state).

➡️ This is a change from gas to liquid.

🔹 Phase Change: Condensation
🔹 Energy: Decrease — Energy is removed to allow particles to come closer together.

✔ Answer:
- Phase Change: Condensation
- Energy: decrease

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✔ Problem 3:

Left image: Particles are tightly packed in a regular pattern (solid state).
Right image: Particles are more loosely arranged and able to flow (liquid state).

➡️ This is a change from solid to liquid.

🔹 Phase Change: Melting
🔹 Energy: Increase — Energy is added to break the rigid structure of the solid.

✔ Answer:
- Phase Change: Melting
- Energy: increase

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✔ Final Answers Summary:

| # | Phase Change | Energy |
|---|------------------|--------------|
| 1 | Freezing | decrease |
| 2 | Condensation | decrease |
| 3 | Melting | increase |

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🧠 Key Takeaway:

- When matter gains energy, it moves toward higher disorder (e.g., solid → liquid → gas).
- When matter loses energy, it becomes more ordered (e.g., gas → liquid → solid).

So:
- Melting, Vaporization, Sublimation = Energy increases
- Freezing, Condensation, Deposition = Energy decreases

This worksheet correctly identifies all three phase changes with the correct energy trend! ✔️