The document discusses different types of phase changes:
1) Evaporation is when liquid changes to gas as molecules gain kinetic energy and leave the surface. Boiling is evaporation occurring within the liquid as bubbles form.
2) Condensation is the opposite, when gas changes to liquid as high energy gas molecules hit the liquid surface.
3) Melting is when a solid changes to a liquid as heat is absorbed and molecules vibrate more. Freezing is the reverse as energy is removed and molecules slow down.
4) Sublimation and deposition involve direct changes between solid and gas phases.
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Change of phase fall 2010
1. Agenda
Bell work
• Pass in Lab Reports
• Notes: Change of
Phase
• States of Matter Phet
Simulation
• Define Specific Heat
Capacity
• Distinguish between High
and Low Specific Heat.
• Give an example of each
• How does water’s Specific
heat control earth’s climate
• What is special about
Islands and Peninsula's?
5. Heat Transfer
When matter changes phase, a transfer of
thermal energy is involved
6. Evaporation
Liquid changes to gas
Molecules that gain
kinetic energy at the surface
get bumped free
Becomes gas phase above
the liquid
7. Evaporation
Molecules that leave the liquid have the
most energy
Energy of the liquid decreases
Temperature of the liquid goes down
EX. Perspiration
8.
9. Would evaporation be a cooling process if
there were no transfer of molecular energy
from water to the air above?
10. Boiling
Evaporation occurring within a liquid as
well as its surface
Bubbles of vapor form
in the liquid and are
buoyed to the surface,
where they escape
11. Boiling like evaporation is a cooling
process
Boiling water is in thermal equilibrium
It is being cooled by
boiling as fast as it
is being heated by
energy from the
heat source
12. Since boiling is a cooling process, would it
be a good idea to cool your hot, sticky
hands by dipping them into boiling water?
13. Condensation
Gas to a Liquid
High energy molecules close to the surface
become attracted to the liquid
Hit the surface with increased kinetic energy
Raising the temperature of the water
Gas has a lot of energy to give up
14.
15. If the water level in a dish of water remains
unchanged from one day to the next, can
you conclude that no evaporation or
condensation is taking place?
16. Melting and Freezing
Melting - solid to a liquid
heat is absorbed the molecules vibrate
more and more breaking the attractive
forces
17. Freezing - liquid to a solid
energy is taken from the liquid, molecular
motion slows down
attractive forces between
them bind them together
18. Sublimation
Molecules jump directly from
solid phase
to gaseous phase
Snow and ice melting on a hot sunny day
Dry ice in air