Transcript Document
Phase Changes
Any time the state of matter changes,
intermolecular forces are “created or destroyed”
This requires energy (think temperature or
pressure).
Phase Changes
Evaporation
vs.
Boiling
Evaporation
occurs when
particles at the
surface of a
liquid become a
gas.
[http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_12/FG12_11.JPG]
Phase Changes
Boiling
occurs
when particles
throughout the
liquid become a
gas
[http://whatscookingamerica.net/Foto4/BoilingWater.bmp]
Boiling causes liquid to gas
conversion to occur faster.
[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter10/Text_Images/FG10_12.JPG]
Heating Curve
Graph that shows
temperature of a
substance over
time.
“Plateaus”
represent two
phases present.
Click here for an
animation
[http://dbhs.wvusd.k12.ca.us/webdocs/NChO/NChO-92-Local-30.GIF]
Heating Curve For H2O
or condensing
or freezing
[http://www.bbc.co.uk/schools/ks3bitesize/science/images/sci_dia_21.gif]
Phase Changes & Thermo
q = (m)(s)(ΔT)
But ΔT = 0
during a phase
change
Heat (q) is still
being added so
a different
equation is
needed….
Phase Changes & Thermo
q = (moles of substance)(ΔHphase change)
How much energy does it take to change
54.0 g of ice to liquid water?
Phase Changes & Thermo
• First, find the moles of water:
54.0 g H2O 1 mol H2O
18.0 g H2O
= 3.00 mol H2O
Phase Changes & Thermo
Then, plug into the equation to solve:
q = (3.00 moles)(6.01 kJ/mol)
q = 18.0 kJ of energy
Phase Changes & Thermo
What
if the temperature changes
and the phase changes?
Example:
How much energy does it take to
melt 108 g of ice an heat it to a
temperature of 50.0oC?
Phase Changes & Thermo
q = (moles)(ΔHfus) + (m)(s)(ΔT)
Find the moles of water…
108 g H2O 1 mol H2O
18.0 g H2O
= 6.00 mol H2O
Phase Changes & Thermo
J
kJ
q (6.00 mol)(6.01
) (108g)(4.1
(m) (s) (8T) o ) (50.0o C)
mol
gx C
Phase Changes & Thermo
q
= 36.1 kJ + 22600 J
Or…
q = 58.7 kJ
Phase Diagrams
Graph
that
shows how
pressure and
temperature
affect the
phases of
matter.
[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/me
dia_portfolio/text_images/CH11/FG11_10.JPG]
[http://library.thinkquest.org/C006669/media/Chem/img/Graphs/Phase.gif]
[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH11/FG11_06.JPG]
Phase Diagrams
The
triple point
is where all
three phases of
matter coexist.
Click here for a
video example
[http://tbn0.google.com/images?q=tbn:tA2QLC4fXbJWjM:http://img.sc
oop.co.nz/stories/images/0611/0c994da3e92a18f9a4cb.jpeg]
Dry Ice
CO2 Gas