A student heats 1 kg of water of 20 ^oC in an experiment to learn the phase change of water. Temperature needs to be recorded for each phase.

Assumptions:

• The pressure in the pan stays at 1 atm during the process and thus the saturated temperature is 100 ^oC.
• No water or vapor leaks from the pan. So the system is a closed system.

If the time when the water becomes saturated liquid and saturated vapor are known, then the recording time schedule can be determined.

Q_water is the energy needed to heat the water from subcooled liquid (room temperature) to saturated liquid (saturated temperature).

where
      ΔT_water = T _saturated - T_room
       = The power of the electric heater, is given
                as 2.0 kW

Q_vapor is the total energy needed to heat the room temperature water to saturated vapor.

Using known values,

      ΔT_water = 100 - 20 = 80 ^oC

      t_{saturated liquid} = (1.0) (4.184) (80)/2.0 = 167.36 s

      t_{saturated vapor} = 2257.0/2.0 + 167.36 = 1295.86 s

The time range for each phase is shown in the table.