Transcript Phases of Matter and Phase Changes

Phases of Matter and
Phase Changes
Phase

.
Depends on
strength of forces
of attraction
between particles.
Solids
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Definite shape and volume.
Most dense phase (exception is water!).
Difficult to compress.
Particles vibrate in fixed positions
Regular crystalline lattice structure.
Highest attraction between particles.
Note: Amorphous solids include
glass, plastic, wax, and silly putty
Liquids
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Definite volume
No definite shape
Hard to compress
Particles slide past each
other
Forces of attraction
between particles still high
Gases
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No definite shape or volume
Expands to fill container
Lowest density
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Density depends on pressure
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Little attraction between
particles
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“Vapor” = a gaseous state of
something that is normally liquid
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(Ex: water vapor)
Phases Applet
Short Summary video on phases:
 http://www.youtube.com/watch?v=sKvoVzukHo&safe=active
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http://www.harcourtschool.com/activity/stat
es_of_matter/
Changes in Phase
Gas
Condensation
Vaporization
(Boiling or Evaporating)
Liquid
Solidification
Melting (fusion)
Solid
Let’s Skip a Phase
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Sublimation
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Directly from the solid
phase to the gas phase.
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Happens with substances
with weak intermolecular
forces of attraction
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They separate easily!
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Ex: CO2(s) dry ice, Iodine
CO2(s) → CO2 (g)
http://www.youtube.com/watch?v=8tHOVVgGkp
k
Energy
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Energy = capacity to do work or produce heat.
It can be anything that causes matter to move or
change direction.
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Ex: electrical, atomic, mechanical, chemical
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Energy and the 4 states of matter:
http://www.youtube.com/watch?v=88tK5c0wgH4&safe=active
Law of Conservation of Energy
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Energy can’t be
created or
destroyed, just
transferred from
one form to another
PE vs. KE
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Potential Energy
stored energy
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Energy can be stored
in bonds between
atoms and released
during chemical rxns.
Kinetic Energy
energy of motion
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All atoms are moving
and vibrating unless at
absolute zero
Heat Energy
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A form of energy that increases the random
motion of particles
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Measured in Joules or calories.
http://www.youtube.com/watch?v=f1eAOygDP5s&safe=active
Heat Flow
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Heat energy
travels from an
object of higher
temp. to one of
lower temp. until
both reach the
same temp.
Temperature
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Measure of the average kinetic energy
(motion) of all the particles in a sample.
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Not a form of energy!!!
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But if you add heat energy or take it away, it
causes particles to move faster or slower and
thus changes the temp.
Temperature Scales Used in
Chemistry
Celsius
 Fixed points of scale based on the freezing
point and boiling point of water
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0 °C = water freezes, 100 °C = water boils
Kelvin
 Scale based on lowest temperature possible
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0 K = absolute zero
Temperature
Scales and
Conversions
K = ˚C + 273
Absolute Zero
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Temperature at which particles have
slowed down so much they no longer
possess any kinetic energy.
0 Kelvin
-273° Celsius
Heat vs. Temperature
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Teacup vs. Bathtub
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Both at 25˚C
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Which one contains
more heat energy?
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Which one has the
greater average KE?
Exothermic vs. Endothermic
Changes
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Exothermic Change:
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A + B → C + D + energy
Energy is released or “ex”its
Endothermic Change: A + B + energy → C + D
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Energy is absorbed or “en”ters
Energy During Phase Changes
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Endothermic: (s→l, or l→g)
Energy overcomes attractive forces between
particles
 PE increases
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Exothermic: (g→l, or l→s)
As particles come closer together energy is
released
 PE decreases
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Heating & Cooling Curves
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Graphically represents temp. changes as heat
energy is added or taken away.
Label This Graph
Interpreting the Graph
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The slanted portions =
temp is changing
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Single phase is heating
up or cooling down
KE is changing
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The flat portions =
temp not changing
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Substance undergoing
a phase change
PE is changing
Heating Curve for Water
What is Melting Pt? Boiling Pt?
Heat Equations
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Calculates the energy involved when a
substance changes in temperature or
undergoes a phase change.
Physical Constants for Water
Table B
Use these constants in Heat Equations
Hf = heat of fusion = 334J/g
Hv = heat of vaporization = 2260J/g
Specific Heat Capacity (“c”) = 4.18 J/g x K
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When temperature of substance changes
use this formula:
What is Specific Heat Capacity?
Specific Heat: “c”
Joules of heat needed to raise 1 gram of a
substance 1°C.
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Substances have different abilities to absorb
heat when energy is applied depending on
their composition.
Ex: Piece of Iron vs. Water.
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When Undergoing Phase Change use one of
these formulas: TEMPERATURE CONSTANT
Q
= mHf
Use when changing from
solid to liquid (melting) or
liquid to solid (freezing)
Q
= mHv
Use when changing from
liquid to gas (vaporization) or
gas to liquid (condensing)
Calorimeters
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Instrument used to determine amount of heat lost
or gained in a reaction by measuring changes in
the temp. of water surrounding the system.
Virtual Calorimetry
http://group.chem.iastate.edu/G
reenbowe/sections/projectfolder
/flashfiles/thermochem/heat_me
tal.html
Q = mcΔT
Try This!!
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Online App Demonstrates Specific Heat
and Calorimetry
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http://elearning.classof1.com/demo/2D_Lab/Chemistry/specificHeat/
specificHeat.html
Multi-step Heat Problems (Honors)
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Need to use more than one of the heat
equations and add up the total heat.
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Note: Specific Heat of different phases of water!
= 2.10 J/gx°C
 H2O (l) = 4.18 J/gx°C
 H2O(g) = 1.84 J/gx°C
 H2O(s)
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Ex: Calculate the heat energy to raise 10
grams of water at -25°C to 80°C.
Draw a heating curve. Figure out # of steps.
 1.) Heat ice from -25° to 0°
q = mcΔT
 2.) Melt ice to liquid at 0°
q = mHf
 3.) Heat liquid water from 0° to 80° q = mcΔT
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Heat Lost = Heat Gained (Honors)
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When two objects of different temperatures
are placed together in a closed system,
heat flows from hotter to colder object until
they reach same temperature.
mcΔT = mcΔT
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Total heat lost = total heat gained