Transcript Heat In Changes of State

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
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