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