Energy of Phase Changes

AP Chemistry· difficulty 2/5

Plateau D is much longer than plateau B for water.

Heat added T B D

Why is plateau D longer than B?

  • A

    Vaporization requires more energy than fusion (greater enthalpy change)

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  • B

    Liquid water has a smaller heat capacity

  • C

    Steam absorbs less heat than ice

  • D

    Boiling occurs at a lower temperature

Explanation

The enthalpy of vaporization (<del>40.7 kJ/mol for water) is much larger than the enthalpy of fusion (</del>6.0 kJ/mol), so a longer plateau is required at the same heating rate.

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