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Heating curves and phase changes

−20 °C Start with ice and add heat. The target calorific value is limited to 120 °C. The time is calculated based on target calories/output and plays at double speed for 10 seconds.

    C17 · Heating curves and phase changesReady
    −20 °C Start with ice and add heat. The target calorific value is limited to 120 °C. The time is calculated based on target calories/output and plays at double speed for 10 seconds. You can also experiment with the numbers and controls below.

    Chemistry / Thermochemistry / Principles and Exploration

    Heating curves and phase changes — principles and investigation

    Even if the temperature remains constant during heating, this does not mean that energy is not supplied. Change the mass of water, heating output, and amount of heat input to look at everything from the heating of the ice to changes in its state. This is a heating curve experiment that distinguishes between the heat used to increase temperature and the latent heat used for melting and vaporization.

    How does it work?

    The horizontal section is not a section where heat disappears, but a section used for state changes.

    Key relationship

    Q = mcΔT · Qmelting = mLf · Qvaporization = mLv

    Try this investigation

    1. −20 °C Start with ice and add heat. The target calorific value is limited to 120 °C. The time is calculated based on target calories/output and plays at double speed for 10 seconds.
    2. We record 309.4 kJ overall and 20 kJ during melting. Check the temperature and condition ratio.
    3. Change only the mass to 200 g or change the output to 1000 W. Output changes the time taken instead of the temperature reached for the same amount of heat.

    Interpreting your results

    What is the input heat used for in the 100 °C horizontal section of the heating curve?

    In the latent heat section, the state ratio changes and the temperature remains constant. After evaporation, the temperature of the water vapor rises again.

    Assumptions and limitations

    Source: Standard physical property values ​​(rounded values ​​for educational purposes). One type of water, constant pressure 1 atm, c ice = 2.09, c water = 4.18, c steam = 2.01 J/(g·K), heat of fusion 334 J/g, heat of vaporization 2260 J/g. The specific heat is constant, there is no heat loss, and water vapor remains in the system. Actual pressure changes, superheating, supercooling, and evaporation losses are omitted. The particle spacing is a schematic diagram.