solid liquid gas tightly packed, in a regular pattern vibrate, but do not move from place to place...
TRANSCRIPT
Phase Changes
Overcoming Intermolecular Forces
STATES OF MATTER
SOLID LIQUID GAS
Tightly packed, in a regular
patternVibrate, but do not move from place to place
Close together with no regular arrangement.Vibrate, move
about, and slide past each other
Well separated with no regular arrangement.Vibrate and
move freely at high speeds
What causes a substance to be in solid or liquid state? Attractive forces between particles.
STATES OF MATTER
SOLID LIQUID GAS
Tightly packed, in a regular
patternVibrate, but do not move from place to place
Close together with no regular arrangement.Vibrate, move
about, and slide past each other
Well separated with no regular arrangement.Vibrate and
move freely at high speeds
How do we overcome these attractive forces?
By adding energy (heat) to the particles.
Kinetic Energy & Temperature
Adding energy (heat) makes the particles vibrate or move faster.This kinetic energy (energy of motion) is the basis of temperature.More Kinetic Energy = Higher temperature
Kinetic Energy & Temperature
So why are substances gases at high temperature?The particles are moving faster… There is less opportunity for attractive forces (IMFs) to pull molecules together as solids or liquids.
Kinetic Energy & Temperature
If the substance is in a gaseous state, energy can be removed (it can be cooled down)
As soon particles are moving slowly enough for their kinetic energy to be overcome by attractive forces between them (IMFs), the substance will liquefy or solidify.
Overcoming IMFs with kinetic energy
Heating Curve (water)
Tem
pera
ture
Energy Added
solid
liqui
d
gas
100º C -
0º C -
melting point(s) (l)-
(s) (l)-freezing point
boiling point(l) (g)-
(l) (g)-condensation point
Heating Curve (water)
Tem
pera
ture
Energy Added
Heat of fusion
Heat of vaporization
“Fusion” means melting (fusing bits of solid into a liquid) when it is used to talk about phase changes.
∆Hfusion ∆Hvaporization
Where did the energy go?
Tem
pera
ture
Energy Added
Kinetic energy (T) does not increase during phase change.
The energy that overcomes attractive forces between particles is stored as potential energy.
0º C -
-25º C -
Heating solid(kinetic energy)
Latent heat (heat
of fusion)(potenti
al energy)
Heating liquid(kinetic energy)
Latent heat (heat of
vaporization)
(potential energy)
Phase change energy is often called a “latent” heat. (Latent = hidden)
Heating gas
(kinetic energy)
100º C -
165º C -
MeltingChange from Solid to Liquid
The melting point is the temperature at which a material changes phase from solid to liquid.
Melting occurs when the kinetic energy of individual atoms equals the attractive force between atoms.
Kinetic Energy =
temperature
BoilingChange from Liquid to Gas
The boiling point is the temperature at which a material changes phase from liquid to gas.
Boiling occurs when the kinetic energy of individual atoms causes a vapor pressure equal to atmospheric pressure.
BoilingChange from Liquid to Gas
VAPOR PRESSURE:The pressure exerted by gas molecules of a (specific) substance.
This is temperature dependent. (Vapor pressure increases with temperature.)
So boiling point = the temperature where vapor pressure = atmospheric pressure
Vapor Pressure:
Vapor Pressure:
At the boiling point, bubbles of gas form throughout the liquid.
The bubbles only form if their pressure matches surrounding pressure.
BoilingChange from Liquid to Gas
What’s the boiling temp of chloroform?
Ethanol?
Water?
Ethanoic acid?A substance cannot boil until its vapor pressure = atmospheric pressure.
Standard Pressure: 1 atm = 101.3 kPa = 760 mmHg
60 ºC
80 ºC
100 ºC
120 ºC
“Standard Pressure” = At sea level
We’re not at sea level.Higher altitude =
Thinner air = Lower air pressure.
Our air pressure is about 84.2 kPa.
BoilingChange from Liquid to Gas
What’s the boiling temp of water in Alpine?Air pressure ≈ 84.2 kPa
Boiling point ≈ 95 ºC
Does spaghetti take more time or less time to cook in Alpine, compared to San Diego?
MORE time– because we cook it at a slightly lower temperature.
Phase Diagram
One Graph to Rule them ALL!The phase diagram combines:Temperature/Energy information from a heating curve
Temperature/Pressure
information from a vapor pressure curve.
Temperature
Pre
ssure
Phase Diagram
All phase changes are shown on this graphWhich phase is likely
at low temp?At high temp?At high pressure?
High pressure favors the most dense phase.
Low pressure favors the least dense.
Temperature
Pre
ssure
SOLID
GAS
LIQ
UID
Phase Diagram
All the phase changes:
Temperature
Pre
ssure
SOLID
GAS
LIQ
UIDMelting = fusion
Freezing = crystallization = solidifying
Boiling = evaporation = vaporization
Condensing
Every point on this line is a MP & FP !
Every point on this line is a BP & CP !
Phase Diagram
All the phase changes:
Temperature
Pre
ssure
SOLID
GAS
LIQ
UIDSublimation
(solid to gas)Deposition
(gas to solid) Every point on this line is a SP & DP !
Sublimation From Solid Straight to Gas
Requires the input of energy
Sublimation of snow occurs more readily under at high altitudes with less air pressure, with dry winds.
Examples: dry ice, iodine and snow
Sublimation occurs (on a small scale) in your freezer– when things get freezer burn.
Deposition: from gas to solid (without liquefying)
(The opposite of sublimation)
Deposition of iodine
Requires the release of energy.
Deposition commonly occurs when water vapor freezes to form snow or frost.
(On your windshield, for example.)
This also occurs in your freezer with the freezer burn!
Phase Diagram
“Normal” phase change:
Temperature
Pre
ssure
SOLID
GAS
LIQ
UIDMeans:
Standard Pressure1 atm, 101.3 kPa, 760 mmHg
This graph (for CO2) doesn’t have mp or bp, because CO2 sublimes at 1 atm.
Phase Diagram
Can we force it to boil?
Temperature
Pre
ssure
SOLID
GAS
LIQ
UIDYes! If we raise
the pressure above 5.2 atm, will melt and boil.
If we raise the pressure to exactly 5.2 atm?
Triple point: all three phases coexist. (It boils and freezes!)
Phase Diagram
Critical point
Temperature
Pre
ssure
SOLID
GAS
LIQ
UIDAbove this
temperature, the particles have so much kinetic energy that they ONLY exist in the gas phase.
Even if the graph stops here, assume the line goes straight up.
Phase diagram for water:
The 1 atm line crosses all three phases, so we experience all phases of water.
To reach the triple point, you would need a vacuum chamber. (Or extreme high altitude.)
Boiling Point and Pressure As altitude increases, air
pressure decreases. As air pressure decreases
boiling point decreases.
At what altitude would your food cook most quickly? Hint: at what temperature would
it cook most quickly?
Phase diagram for water:
This is why boiling ramen doesn’t work well for (high altitude) High Adventure camps
The boiling water is not as hot as you hoped… so cooking takes forever.
Heating Curve: At High Altitude
Tem
pera
ture
Energy Added
solid
liqui
d
gas
85º C -
2º C -
melting point(s) (l)-
(s) (l)-freezing point
boiling point(l) (g)-
(l) (g)-freezing point
Even in a raging bonfire, your water will refuse to get any hotter once it’s boiling.
Phase diagram for water:
If only there was a way to increase the pressure…
They can boil water at a temp above 100 ºC, so food cooks faster.
Pressure cookers do that!
Evaporation
Molecules leaving the liquid take energy away from a liquid in order to convert to gas.
The average energy of the molecules left behind is lowered:the temp. of the fluid left behind is lower.
Evaporation can occur when molecules go from liquid to gas at temperatures below the boiling point.
Evaporation cools the surface of a liquid because the fastest molecules escape and carry energy away.
Condensation Condensation can occur when molecules
go from gas to liquid at temperatures below the boiling point. Molecules slow down and begin
to stick together. (Due to IMFs!) As they change from gas to
liquid, the molecules release latent heat to the surroundings Condensation is a heating
process!The release of energy from
condensation drives weather including wind, thunderstorms, hurricanes etc…
Energy and Phase Change