To sketch a heating-cooling curve for water that starts at 220°C and cools down to 120°C while applying heat at a constant rate, we need to break the process down into several key phases. Here’s how to visualize it:
- Initial Heating Phase: From 220°C, as heat is applied, the temperature will rise until it reaches the boiling point of water (100°C). This will be represented as a sloped line moving upwards.
- Phase Change – Boiling: Once the temperature reaches 100°C, water begins to boil. During this phase change, the temperature remains constant while the water transitions from liquid to gas. This will appear as a horizontal plateau on the curve.
- Heating of Steam: After all the water has boiled and turned into steam, applying further heat will increase the temperature of the steam until it reaches 120°C. This section will again show a sloped line moving upward.
In summary, the sketch should depict a warm-up phase leading to evaporation (boiling) where the curve flattens, followed by the steam heating up. To highlight the melting of a solid and boiling of the liquid, you would mark the horizontal segments on the curve as follows:
- Melting Point: If this process included ice melting, it would be marked during the temperature plateau at 0°C on the heating curve.
- Boiling Point: Clearly mark the boiling point at 100°C on the curve, indicating where water turns into steam.
This heating-cooling curve is a vital part of understanding thermodynamics and phase transitions in substances like water.