Phase ChangesPhase Changes Any time the state of matter changes, Any time the state of matter changes,

intermolecular forces are “created or destroyed”intermolecular forces are “created or destroyed” This requires energy (think temperature or This requires energy (think temperature or

pressure).pressure).

Phase ChangesPhase Changes

Evaporation Evaporation vs. Boilingvs. Boiling

Evaporation Evaporation occurs when occurs when particles at particles at the the surfacesurface of of a liquid a liquid become a gas.become a gas.

[http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_12/FG12_11.JPG]

Phase ChangesPhase Changes

Boiling occurs Boiling occurs when when particles particles throughoutthroughout the liquid the liquid become a gasbecome a gas

[http://whatscookingamerica.net/Foto4/BoilingWater.bmp]

[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter10/Text_Images/FG10_12.JPG]

Boiling causes liquid to gas conversion to occur faster.

Heating CurveHeating Curve

Graph that Graph that shows shows temperature of temperature of a substance a substance over time.over time.

““Plateaus” Plateaus” represent two represent two phases present.phases present.

Click here for an animation

[http://dbhs.wvusd.k12.ca.us/webdocs/NChO/NChO-92-Local-30.GIF]

[http://www.bbc.co.uk/schools/ks3bitesize/science/images/sci_dia_21.gif]

or condensing

or freezing

Heating Curve For H2O

Phase Changes & ThermoPhase Changes & Thermo

q = (m)(s)(q = (m)(s)(ΔT)ΔT) But ΔT = 0 But ΔT = 0

during a during a phase changephase change

Heat (q) is still Heat (q) is still being added being added so a different so a different equation is equation is needed….needed….

Phase Changes & ThermoPhase Changes & Thermo q = (moles of substance)(q = (moles of substance)(ΔΔHHphase changephase change)) How much energy does it take to How much energy does it take to

change 54.0 g of ice to liquid water?change 54.0 g of ice to liquid water?

Phase Changes & ThermoPhase Changes & Thermo

54.0 g 54.0 g HH22OO 18.0 g 18.0 g

HH22OO

1 mol 1 mol HH22OO = 3.00 mol = 3.00 mol

HH22OO

• First, find the moles of water:First, find the moles of water:

Phase Changes & ThermoPhase Changes & Thermo Then, plug into the equation to solve:Then, plug into the equation to solve: q = (3.00 moles)(6.01 kJ/mol)q = (3.00 moles)(6.01 kJ/mol) q = 18.0 kJ of energyq = 18.0 kJ of energy

Phase Changes & ThermoPhase Changes & Thermo

What if the temperature What if the temperature changes changes andand the phase the phase changes?changes?

Example:Example: How much energy does it take How much energy does it take

to melt 108 g of ice an heat it to melt 108 g of ice an heat it to a temperature of 50.0to a temperature of 50.0ooC?C?

Phase Changes & ThermoPhase Changes & Thermo

q = (moles)q = (moles)((ΔHΔHfusfus))

+ (m)(s)(+ (m)(s)(ΔT)ΔT)

Find the moles of water…Find the moles of water…

108 g 108 g HH22OO 18.0 g 18.0 g

HH22OO

1 mol 1 mol HH22OO = 6.00 mol = 6.00 mol

HH22OO

Phase Changes & ThermoPhase Changes & Thermo

)molkJ

mol)(6.01 (6.00 q T)( (s) (m) C)(50.0 )Cgx

J8(108g)(4.1 o

o

Phase Changes & ThermoPhase Changes & Thermo

q = 36.1 kJ + 22600 Jq = 36.1 kJ + 22600 J Or…Or… q = 58.7 kJq = 58.7 kJ

Phase DiagramsPhase Diagrams

Graph that Graph that shows how shows how pressure and pressure and temperature temperature affect the affect the phases of phases of matter.matter.

[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_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 DiagramsPhase Diagrams

The The triple triple pointpoint is where is where all three all three phases of phases of matter matter coexist.coexist.Click here for a v

ideo example

[http://tbn0.google.com/images?q=tbn:tA2QLC4fXbJWjM:http://img.scoop.co.nz/stories/images/0611/0c994da3e92a18f9a4cb.jpeg]

Dry Ice CO2 Gas