Worksheet on heating curves and phase diagrams for analyzing physical changes in substances.

Final Answer:
1. 5 °C
2. 15 °C
3. a
4. e
5. b
6. d
7. Liquid
8. Condensation (gas → liquid), then freezing (liquid → solid)
9. Decrease the pressure below 0.0060 atm (to enter the vapor region)
1) 0 °C and ~0.006 atm (triple point)
3) It will become a gas (vaporize)
4) Because at 200 °C, compound X is already a gas at all pressures below its critical pressure — there’s no liquid phase to boil; boiling requires liquid → gas at the boiling point, but above the critical temperature, liquid doesn’t exist.
5) No — because at room temperature and pressure, compound X is a gas (see phase diagram: at ~25 °C and 1 atm, it's in the gas region).