Worksheet on the heating curve of water, detailing phase changes and temperature variations during heating.

Final Answer:
1. Stage 1: s
 Stage 2: s + l (melting)
 Stage 3: l
 Stage 4: l + g (boiling)
 Stage 5: g

2.
 ① = Temp Change
 ② = Phase Change
 ③ = Temp Change
 ④ = Phase Change
 ⑤ = Temp Change

3. a) At the end of stage 2 (just before stage 3 begins), all ice is gone — temperature ≈ 0°C
 b) At the end of stage 4 (just before stage 5 begins), all liquid is gone — temperature ≈ 100°C

4. Yes, for most pure substances with similar phase behavior (e.g., ethanol, iron), heating curves show flat plateaus during melting/boiling and rising slopes during temp changes — because energy goes into breaking bonds (phase change) or increasing kinetic energy (temp change).

5. The added heat energy is used to overcome intermolecular forces (e.g., hydrogen bonds in water) — this is called latent heat. It doesn’t raise temperature because molecules aren’t moving faster; they’re changing arrangement (solid → liquid or liquid → gas).

6. It takes more heat to boil water completely than to melt ice.
 Reason: Latent heat of vaporization (≈2260 J/g for water) > latent heat of fusion (≈334 J/g). So boiling needs ~6.8× more energy per gram than melting.

7.
 A = melting
 B = solid → liquid (solid & liquid present)
 C = condensation
 D = freezing
 E = gas
 F = liquid
 G = solid

8.
 A (melting): Endothermic
 C (condensation): Exothermic
 D (freezing): Exothermic