Heat In Changes of State of Matter 17.3

What happens during a phase change: When heat energy is added, instead of increasing the temperature (increasing the kinetic energy of the molecules), the intermolecular bonds are broken, changing the phase of the substance.

PHASES OF WATER

Q = mHf Heat of Fusion (Hf) Amount of heat necessary to convert a given amount of a solid into a liquid Q = mHf

Fusion Heat that is absorbed for a solid becomes a liquid Melting, endothermic Reverse process is Solidification Heat is released, exothermic

Practice Problems Answer 21 and 22 in notes on page 521 Hint 21 is the reverse of 20 Look at the Table on pg.522

Heat of Vaporization (Hv) Amount of heat necessary to vaporize a given amount of liquid at its boiling point Q = mHv

Vaporization and Condensation When a liquid absorbs heat at its boiling point it will vaporize. The surroundings cool because the liquid is absorbing heat Heat of vaporization is 40.7 Kj/mol Condensation is opposite of vaporization

Vaporization and Condensation Heat of vaporization is endothermic Condensation is exothermic

Practice Problems Answer problems 23 and 24 in notes Hint you need the molar mass of chloroethane

Heat of Solution Heat changes occur when a solute dissolves in a solvent An example is a hot pack, which is exothermic An example of endothermic is ammonium nitrate dissolving in water, frost can form

Practice Problems Answer problems 25 and 26 in your notes

Activity Show on a piece of paper, the changes in states of matter for a piece of ice to go to water vapor and back to ice again. Use your vocab terms to describe steps in a diagram