Heating Curve Worksheet: Understanding Phase Changes and Energy Absorption During Heating.

Let’s go step by step through the heating curve.

The graph shows temperature vs. time as a substance is heated at a constant rate, starting from -10°C.

We know:
- When temperature is rising (sloped lines), the substance is in one phase and gaining kinetic energy → particles move faster.
- When temperature stays flat (horizontal lines), the substance is changing phase → energy goes into breaking bonds (potential energy), not raising temperature.

Looking at the graph:

Segment ①: Flat line at 0°C → this is melting (solid to liquid). Temperature doesn’t change during phase change.

Segment ②: Sloping up from below 0°C to 0°C → solid warming up.

Wait — let’s label the segments correctly based on standard heating curves:

Actually, looking again:

Starts at -10°C → rises to 0°C (segment ) → then flat at 0°C (segment ①? Wait, numbering might be off.)

Hold on — the diagram labels the segments with numbers inside circles:

From left to right:

- Segment ②: sloping upward from -10°C to 0°C → solid heating up
- Segment ①: horizontal at 0°C → melting (solid ⇌ liquid)
- Segment ③: sloping upward from 0°C to 100°C → liquid heating up
- Segment ④: horizontal at 100°C → boiling (liquid ⇌ gas)
- Segment : sloping upward above 100°C → gas heating up

But wait — the question asks about segment (1) first.

In the diagram, segment labeled “①” is the first horizontal part — that’s at 0°C.

So:

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Question 1a: What phase or phases are present during segment (1)?

Segment ① is horizontal at 0°C → this is the melting point. During melting, both solid and liquid coexist.

→ Answer: Solid and liquid

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Question 1b: What is happening to the energy being absorbed... in terms of potential and/or kinetic energy?

During phase change (melting), temperature doesn’t rise → so kinetic energy isn’t increasing. The energy is used to break intermolecular forces → that increases potential energy.

→ Answer: Potential energy is increasing; kinetic energy is not changing.

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Question 1c: What phase change, if any, is taking place?

At 0°C, going from solid to liquid → melting.

→ Answer: Melting (or fusion)

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Now Question 2:

Question 2a: What phase or phases are present during segment (2)?

Segment is the sloped line BEFORE segment — it goes from -10°C up to 0°C. So this is still solid, just getting warmer.

→ Answer: Solid only

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Question 2b: What is happening to the energy...?

Temperature is rising → particles moving faster → kinetic energy increasing. No phase change → potential energy not changing significantly.

→ Answer: Kinetic energy is increasing; potential energy is not changing.

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Question 2c: What phase change, if any, is taking place?

No flat line here — temperature is changing → no phase change occurring.

→ Answer: None

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Final check: All answers match standard heating curve behavior.

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Final Answer:
1a) Solid and liquid
1b) Potential energy is increasing; kinetic energy is not changing
1c) Melting
2a) Solid
2b) Kinetic energy is increasing; potential energy is not changing
2c) None