Sublimation and Deposition
Solid to
gaseous/vapor form
Vapor to solid
Describe what happens
to the particles during
this process. Explain
why this happens.
Dry Ice
The Iodine Test
Iodine test:
http://www.youtube.com/watch?v=4fAOI6BeMZY
Activity 1. Evaporation of Liquids
Evaporation happens
when atoms or
molecules escape
from the liquid and
turn into a vapor.
Describe what happens
to the particles during
this process. Explain
why this happens.
Activity 1. Evaporation of Liquids
Which liquid will evaporate fastest?
Water, Oil, Alcohol?
Hypothesis: ____________________
Design a simple test. Set-up your experiment.
Notes Next Slide
What factors can affect the rate
of evaporation?
The energy you can measure
with a thermometer is an
average of all the molecules
in the system.
There are always a few
molecules with a lot of
energy and some with barely
any energy at all.
NATURE OF THE SUBSTANCE
Alcohol
Water
Oil
Some liquids have __________ forces that hold
particles together allowing some particles to
escape.
What factors can affect the rate
of evaporation?
The molecules with a lot of energy are able to build
up enough power to become a gas. Once they
reach that energy level, they can leave the liquid
and thus, it has evaporated.
Force of air
pressing
down
Factors affecting the rate of evaporation
Image source: http://www.vtaide.com/png/evaporation.htm
Applying Understanding: Real-life situations
Why do you spread out
your wet clothes to dry?
Why do you feel cool
when you stand next to a
fan?
Why do you feel cold
when you immediately
step out of the shower?
Why is it important to “
rehydrate? Relate
“sweating” to evaporation
and our body’s ability to
regulate temperature.
Activity 2. Freezing Point of Liquids
Which liquid will freeze the fastest?
Water, Alcohol, Diet Soda, Regular Soda, Coolant?
Hypothesis: ____________________
Design a simple test. Set-up your experiment.
extra
Notes Next Slide
FREEZING POINT
Change in phase from
liquid to solid
Image source: http://www.factfrenzy.com/what-is-thefreezing-point-of-water/
Particles slow down
Particles of
a liquid
Particles fuse
Why?
When energy is taken
out from a liquid,
particles slow down
until forces of attraction
cause them to fuse and
form a solid.
Substance
Water
Diet Soda
Regular Soda
Freezing Point (degrees Celsius)
0
Slightly lower than 0
Lower than 0 (b/n -15 to -20)
Coolant
-37
Alcohol (Isopropyl)
- 88
Mineral Oil
-30
Why is salt added to a
snow-covered driveway?
Activity 2. Freezing Point of Liquids
Why add salt to a snow-covered driveway?
Hypothesis: ____________________
Design a simple test. Set-up your experiment.
Salt dissolves in water pretty fast. When you sprinkle salt on
ice, the salt lowers the freezing point of the water, keeping it
from re-freezing as easily and helping to melt the rest of the
ice. This is called lowering the freezing point.
When you add salt to water, the salt (called sodium chloride,
NaCl) dissolves into particles (actually called ions of sodium
and chloride). The freezing point of water becomes lower as
more particles are added until the point where the salt stops
dissolving. On a driveway or street, sodium chloride can melt
ice only down to about (-9°C).
http://www.stevespanglerscience.com/experi
ment/how-does-salt-melt-ice
BOILING POINT
Evaporation takes
place at surface
of liquids
Boiling takes
place beneath
surface of liquid
This animation shows how water molecules
are able to break the forces of attraction .
This is what is happening inside the gas bubble
as it is rising to the surface to break and
release the water gas molecules.
Image source: http://www.elmhurst.edu/~chm/vchembook/163boilingpt.html
Animated GIF "Boiling" - Courtesy of General Chemistry Help - Purdue University
In a liquid, molecules are
packed closely together. As
a liquid is heated, the
temperature is increased.
As the temperature
increases, the kinetic
energy increases which
causes increasing motion.
Eventually molecules break
free of liquid and become a
gas. At the temperature of
the boiling point, the liquid
turns into a gas.
Activity 2. Boiling Point of Liquids
How does a coolant help
prevent overheating?
Car Engine
Activity 2. Boiling Point of Liquids
Aim: How does a coolant help
prevent overheating?
Lab Demo:
Observations:
Explanation:
Water
Coolant
How does pressure affect the boiling point?
http://www.youtube.com/watch?v=9q5gEZGoBnk Vacuum Chamber
Physics in the Kitchen
How
does a
pressure
cooker
work?
Physics in the Kitchen
•It is the high temperature that
cooks the food.
• Pressure affects boiling.
Increased pressure raises the BP.
• Pressure cookers increase the
pressure inside and prevent
boiling.
• The increased temperature cooks
food faster.
Never boil water in a Microwave
Source: http://www.stevespangler.com/teaching-moments/warning-water-can-explode-in-the-microwave/
A man decided to have a cup of instant coffee, so he
heated a cup of water in the microwave. When the
timer went off, he removed the cup from the
microwave and noticed that the water had not boiled.
Just then, the water literally “blew up” in his face. His
whole face was blistered with first and second degree
burns, which left some permanent scaring and
damage to his left eye.
While at the hospital, the doctor attending him stated
that his is a fairly common occurrence. Water (alone)
should never be heated in a microwave oven.
Never boil water in a Microwave
Source: http://www.stevespangler.com/teaching-moments/warning-water-can-explode-in-the-microwave/
Why? This phenomenon is known as superheating. It can
occur anytime water is heated - especially if the cup or bowl
is new. What happens is that the water heats faster than the
vapor bubbles can form. If the cup is very new, then it is
unlikely to have small surface scratches in it that provide a
place for the bubbles to form (called nucleation sites).
Without bubbles, the water cannot release the heat that has
built up, the liquid does not boil, and it continues to heat up
past its boiling point. If the water is bumped or jarred, it's
enough of a shock to cause the bubbles to rapidly form and
the result is an exploding liquid that is scalding hot. One
solution is to place a wooden stir stick or something nonmetallic in the water to help spread the energy as it is
heating in the microwave.