Phase Change Worksheet featuring a temperature-time graph that demonstrates the heating of a substance, highlighting key points and phase changes.

Let's solve the Phase Change Worksheet step by step, using the provided graph and information.

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🔍 Understanding the Graph

The graph shows temperature (°C) vs. time (minutes) for a substance being heated at a constant rate. Key features:

- Flat horizontal lines indicate phase changes (melting or boiling), where temperature stays constant while energy is used to change state.
- Sloped lines show temperature increasing in a single phase (solid, liquid, or gas).
- The melting point is the temperature where solid → liquid (flat line around 70°C).
- The boiling point is the temperature where liquid → gas (flat line around 140°C).

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✔ Answering Questions 1–22

> 1–22. At point A, the beginning of observations, the substance exists in a solid state. Material in this phase has _________ volume and _________ shape. With each passing minute, _________ is added to the substance. This causes the molecules of the substance to _________ more rapidly which we detect by a _________ rise in the substance. At point B, the temperature of the substance is _______ °C. The solid begins to _________. At point C, the substance is completely _________ or in a _________ state. Material in this phase has _________ volume and _________ shape. The energy put to the substance between minutes 5 and 9 was used to convert the substance from a _________ to a _________. Between 9 and 13 minutes, the added energy increases the _________ of the substance. During the time from point D to point E, the liquid is _________. By point E, the substance is completely in the _________ phase. Material in this phase has _________ volume and _________ shape. The energy put to the substance between minutes 13 and 18 converted the substance from a _________ to a _________ state. Beyond point E, the substance is still in the _________ phase, but the molecules are moving _________ as indicated by the increasing temperature.

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Now fill in the blanks based on the graph and concepts:

1. At point A, the substance is solid:
- Definite volume
- Definite shape

2. Energy is added: Heat (or thermal energy)

3. Molecules vibrate more rapidly

4. We detect a temperature rise

5. At point B: temperature = 70°C (from graph — flat line starts at ~70°C)

6. Solid begins to melt

7. At point C: substance is completely liquid or in a liquid state

8. Liquid has definite volume and no definite shape (takes container shape)

9. Energy between 5–9 min converts solid → liquid (melting)

10. Between 9–13 min: energy increases the temperature of the liquid

11. From D to E: liquid is boiling (phase change from liquid to gas)

12. By point E: substance is completely in the gas phase

13. Gas has no definite volume and no definite shape

14. Energy between 13–18 min converts liquid → gas (vaporization)

15. Beyond point E: substance is in gas phase, molecules are moving faster (as temperature rises)

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✔ Final Answer for 1–22:

> At point A, the beginning of observations, the substance exists in a solid state. Material in this phase has definite volume and definite shape. With each passing minute, heat is added to the substance. This causes the molecules of the substance to vibrate more rapidly which we detect by a temperature rise in the substance. At point B, the temperature of the substance is 70 °C. The solid begins to melt. At point C, the substance is completely liquid or in a liquid state. Material in this phase has definite volume and no definite shape. The energy put to the substance between minutes 5 and 9 was used to convert the substance from a solid to a liquid. Between 9 and 13 minutes, the added energy increases the temperature of the substance. During the time from point D to point E, the liquid is boiling. By point E, the substance is completely in the gas phase. Material in this phase has no definite volume and no definite shape. The energy put to the substance between minutes 13 and 18 converted the substance from a liquid to a gas state. Beyond point E, the substance is still in the gas phase, but the molecules are moving faster as indicated by the increasing temperature.

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✔ Question 23: Which substance was likely used?

Given table:

| Substance | Melting Point | Boiling Point |
|---------------|----------------|----------------|
| Bolognium | 20°C | 100°C |
| Unobtainium | 40°C | 140°C |
| Foosium | 70°C | 140°C |

From the graph:
- Melting occurs at 70°C
- Boiling occurs at 140°C

So, the substance must have:
- Melting point = 70°C
- Boiling point = 140°C

That matches Foosium.

✔ Answer: Foosium

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✔ Final Answer for 23:

> Foosium

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📌 Summary

- Melting point: 70°C → corresponds to Foosium
- Boiling point: 140°C → also matches Foosium
- Therefore, the substance used is Foosium

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✔ Complete Answers:

1–22:
definite, definite, heat, vibrate, temperature, 70, melt, liquid, liquid, definite, no definite, solid, liquid, temperature, boiling, gas, no definite, no definite, liquid, gas, gas, faster

23: Foosium

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