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NOTES

Q: In the example of heating a gram of water, why there are two vertical lines where the temperature is not changing but the energy is; particularly take note of the large vertical line indicated by the arrow.

A:

• The first is a change of state from solid to liquid (ice to water - 80cals) - Click Animation.
• The second is a change of state from liquid to gas (water to steam - 540cals) - This is known as the heat of vaporization.

The conversion to steam requires as much energy as raising the same amount of liquid water from 0°C to 100°C 5.4 times.

Note there is no change in temperature, just a change in state and energy.