Things To Do Now: 1 Unit 3: Phases of Matter Lesson 1: Phases and Phase Change 2 Hot, Cold, &...
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Transcript of Things To Do Now: 1 Unit 3: Phases of Matter Lesson 1: Phases and Phase Change 2 Hot, Cold, &...
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Things To Do Now:
Unit 3: Phases of MatterLesson 1: Phases and Phase Change
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Hot, Cold, & Sublime
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It’s all about ChargesWe talk about “charges” in chemistry...a
lot!
Charges are electrical forces
Charges are either positive (+) or negative (-)
Opposite charges attract, like charges repel.
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Intermolecular Attractive ForcesIntermolecular Attractive Forces=
Any forces (charges) that work to hold particles of a substance together.
Stronger Intermolecular forces = The more energy needed to separate the particles of a substance.
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Phases of MatterThere are 3 phases of matter (on
Earth, normally):– Solids– Liquids–Gasses
These are arranged in order of distance between particles.
How do you move between phases of a substance?
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Solidsa) Particles are arranged into a regular,
geometric pattern (a crystal lattice).
b) Particles vibrate in place. c) Substance has a definite shape & a
definite volume.
Highly Scientific Particle Diagram of A Solid
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Liquidsa) Particles can flow past each other.b) Resistance to flow is called viscosity.c) Viscosity increases as temperature
decreases and IMAF strength increases.d) Evaporation- liquid particles escape into
the gas phase below the boiling point.e) Take the shape of the container, definite
volume.
Highly Scientific Particle Diagram of A liquid
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Gassesa) Gas particles are extremely far apart. b) Gas particles travel in a straight line until they
collide. c) Collisions are elastic which means they don’t lose
any energy or speed.d) Gas particles move faster when it’s hotter (higher
Kelvin temperature)e) The only phase that is affected by changes in
pressure. f) Takes the shape and volume of whatever container
they are put into.
Highly Scientific Particle Diagram of A Gas
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Phase Change Diagram (Learn It!)
S L GMelting Vaporization
Freezing Condensation
Sublimation
Deposition
Melting = “Fusion”Freezing = “Solidification”
Endothermic
Exothermic
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EquilibriumAny time the rates of opposing processes
are equal, those processes are said to be in equilibrium.
Phase Equilibrium:Exists at a substances melting point
(for solid and liquid phases), and boiling point (for liquid and gas phases).What’s in equilibrium at these temps?
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SublimationCan happen in a lot of substances.Most noticeable in substances that
have very weak Intermolecular Attractive Forces.
Highly Scientific Sublimation Particle Diagram
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Heating CurvesA characteristic graph that you get
when heating a substance from a solid to a gas.
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A Few QuestionsWhy isn’t the temperature increasing
during phase changes?
Why does it take longer to go from liquid to gas than from solid to liquid?
What would a cooling curve look like?
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Water’s Heating Curve
What is water’s melting point in Kelvin? What is its boiling point?
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Questions You Need To Answer• How many minutes pass from the
first appearance of the liquid phase until the substance is entirely in the gas phase?
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• How many minutes will it take for this substance to undergo melting?
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• For how many minutes is the water completely in a phase made of a crystal lattice?
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• What line segment represents when H2O is both in the liquid AND the gas phase?
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• For how many minutes is the water completely in a phase with no definite shape or volume?
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• How many minutes will it take for the water to boil, once the boiling point temperature has been reached?
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Things To Do Now:
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Unit 3: Phases of MatterLesson 2: Energy Required for Phase Change
Behold!
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Consider Melting & Boiling.• What happens during each?
• Endothermic or exothermic?
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Consider Freezing & Condensing.• What happens during each?
• Endothermic or exothermic?
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Heat of Fusion (Hf)The amount of heat needed to melt one
gram of a substance at its melting point.
ALSO...The amount of heat needed to be removed from one gram of a substance at its freezing point.
This is on Table B of your Reference Tables.Hf of H2O = 334 J/g
What is water’s melting point?
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Fun With HfWe can use Hf to calculate how much heat
is needed to melt any amount of a substance
AND how much heat is released when any amount of a substance freezes
This is on Table T of your Reference Tables.
q = m Hf
m = mass of substance in grams
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How many joules does it take to melt 100. grams of water at its melting point?
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How many joules does it take to freeze 50.0 grams of water at its freezing point?
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Heat of Vaporization (Hv)The amount of heat needed to boil one
gram of a substance at its boiling point.
ALSO The amount of heat needed to be removed from one gram of a substance to freeze it at its freezing point.
This is also on Table B of your Reference Tables.
Hv of H2O = 2260 J/g
What is water’s boiling point?
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Fun With HvWe can use Hv to calculate how much heat
is needed to melt any amount of a substance
AND how much heat is released when any amount of a substance condenses
This is also on Table T of your Reference Tables.
q = m Hv
m = mass of substance in grams
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How many joules are required to boil 100. grams of water at its boiling point?
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How many joules does it take to condense 50.0 grams of water at its boiling point?
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Putting It All TogetherHow many joules are required to heat
100.0 grams of H2O (s) from –20.00oC to 130.00oC?
Visualize What’s Happening:
PS- C(ice) & C(steam) ≅ 2.09 J/g°C
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Multiple Equations Are Required
1. 2. 3. 4. 5.
1. q = m C(ice) ΔT2. q = m Hf
3. q = m C(water) ΔT4. q = m Hv
5. q = m C(steam) ΔT
What do we do next?
Add It All Up!
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Things To Do Now:
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Unit 3: Phases of MatterLesson 3: Gasses and Pressure
Why Balloons Float(and why they don’t)
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How does a gas behave?
Kinetic Molecular Theory (KMT)-Describes an “ideal” gas.
We imagine how it would behave.It would have five properties:1. Be made of particles with negligible
volume2. Particles move in random, straight-lines3. Completely elastic collisions4. No intermolecular attractive forces5. Speed of particles is directly
proportional to Kelvin temperature
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Ideal is not RealReal gasses violate some/all of the KMT
But-Only when the particles are
moving slow and are squeezed together.
Low Temperature & High Pressure = Non-Ideal Behavior
When would this happen?
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They all contain equal numbers of molecules!!!
Amedeo Avogadro(1776 – 1856)
Avogadro’s Hypothesis
How can this be?!?
Equal numbers of gas particles occupy equal volumes of space under the same conditions of temperature and pressure.
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Standard Temperature and Pressure (STP)Because things happen differently at
different temperatures and pressures (particularly for gasses), we have to set a standard reference point.
Standard Temperature:0° C = 273 K
Standard Pressure:1.000 atm = 101.3 kPa = 760 mmHg
(torr)
These are in Reference Table A.
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What is this “Pressure” of which we speakPressure =
Force exerted over an area.
Anything with mass can exert a force.This includes the atmosphere.
Standard Pressure:1 atmosphere of pressure (at sea level)=
14.7 pounds per square inch (psi).
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Brief notes on Torr.Torr = millimeters of mercury (mmHg)
Refers to the column of
mercury in a barometer. 760 torr
= Standard pressureWhy do we
use mercury?
Evangelista Torricelli(1608 – 1647)
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Pressure conversions1.000 atm = 14.7 psi = 101.3 kPa =
760.0 mmHgConvert 2.35 atm to kPa:
Convert 1.234 kPa to atm:
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Vapor PressureWhen a liquid in a sealed container is at
vapor-liquid equilibrium, the vapor exerts a pressure (like any gas).
Stronger IMAF = Lower vapor pressure.
Higher vapor pressure = faster rate of evaporation.
Volatile=Substances that evaporate quickly.
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Why do things boil?Boiling happens when the vapor
pressure of a liquid is greater than the atmospheric pressure the liquid is under.
Boiling Point =Vapor pressure = atmospheric
pressure.How Can you
increase vapor pressure?
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Normal Boiling PointThe boiling point of a liquid at Standard
Atmospheric Pressure.
What happens to boiling point if atmospheric pressure increases? Decreases?
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Reference Table H
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Problem: What is the vapor pressure of ___ at ___°C?
Use Method A!
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Problem: What is the boiling point of ___ at a pressure of ___kPa?
Use Method B!
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Problem: What is the normal boiling point of ___?
Use Method C!
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What now?Amedeo Avogadro
(1776 – 1856)
Equal numbers of chemistry students, occupying equal volumes of classrooms do
not possess equal numbers of questions....You?
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Things To Do Now:
Unit 3: Phases of MatterLesson 4: Partial Pressure and Effusion
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Passing Gases
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Dalton’s Law of Partial Pressures
NOT in your Reference Tables (memorize!)
Ptotal = PgasA + PgasB + PgasC + ...
John Dalton(1766 – 1844)
The total pressure exerted by a mixture of gasses is equal to the sum of the pressures exerted by each gas in the mixture.
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Practice Helps Us Learn!1) What is the total pressure of a mixture of O2 (g), N2
(g) and NH3 (g) if the pressure of the O2 (g) is 20. kPa, N2 (g) is 60. kPa and the NH3 (g) is 15 kPa?
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2) A mixture of 1 mole of O2 and 2 moles of N2 exerts a pressure of 150. kPa. What is the partial pressure of each gas?
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3) A mixture of 30.0% He and 70.0% Ar exerts a pressure of 150 kPa at 25oC. What is the partial pressure of each gas?
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4) A sample of NH3 (g) is decomposed into its component elements. If the pressure of the nitrogen gas produced equals 40.0 kPa, what would the pressure of the hydrogen gas?
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Graham’s Law of Effusion
The heavier the gas molecules, The greater the gas density.
Table S – Densities (and boiling points) for most elements.
Thomas Graham(1805 – 1869)
Lighter gas molecules will spread out (effuse) faster than heavier gas molecules.
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Mathematical Form of Graham’s Law
ALSO NOT in your Reference Tables!
(ALSO MEMORIZE IT!)
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The Kind of Thing You Need To Do:A closed container of a mixture of
chlorine, fluorine, neon and helium gases is opened so the gases can escape. Place the gases in order of increasing rate of effusion.
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What now?
John Dalton(1766 – 1844)
The total questions asked by a class of chemistry students equals the sum of the questions asked by each student in the class. Any Questions?
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Things To Do Now:
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Unit 3: Phases of MatterLesson 5: The Gas Laws
Imagine a Piston...
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Gases Obey Physical LawsThis should not surprise you.
The behavior of gases can be predicted and expressed according to mathematical relationships.
We will look at relationships of Pressure, Volume, Temperature and the # of molecules (aka moles) of a gas.
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A Brief Note on UnitsWe will use the following units:
Pressure-Atmospheres(atm) & KiloPascals(kPa)
Volume-Liters(L) and milliliters(ml)
Temperature-Kelvin(K)
# of molecules-Moles(mol)
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The Beginning: Avogadro’s HypothesisAll of the gas laws stem from Avogadro’s
Hypothesis:
Amedeo Avogadro(1776 – 1856)
Equal numbers of gas particles occupy equal volumes of space under the same conditions of temperature and pressure.
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2 Illustrative Problems to Consider1. Consider two 4.00 L containers, each at 298
K and 1.00 atm. Container A holds nitrogen gas, Container B holds carbon dioxide gas. If container A holds 2.00 moles of nitrogen gas, how many moles of carbon dioxide must be present in container B?
2. Do equal volumes of gases under the same conditions of temperature and pressure have the same MASS? Why or why not?
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How To Solve Any Gas Law Problem1. Get rid of the words!
Read the problem and pick out the variables. Make a list of them.Make sure your units are acceptable and agree.
2. Write down the particular Gas Law you need.
3. Rearrange to isolate the variable you’re solving.
4. Plug in your numbers.5. Solve and Round to sig. figs.6. Rejoice.
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Boyle’s Law: Pressure & Volume
Temperature must be constant
Robert Boyle(1627 - 1691)
As Pressure Increases, Volume DecreasesP x V = k (a
constant)P1V1 = P2V2
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A sample of gas occupies a volume of 2.00 L at STP. If the pressure is increased to 2.00 atm at constant temperature, what is the new volume of the gas?
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Charles’ Law: Temperature & Volume
Jacques Charles(1746 - 1823)
As Temperature Increases, Volume IncreasesV/T = k (a constant)V1/T1 = V2/T2
Pressure must be constant
TEMP MUST BE KELVIN
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A sample of gas occupies a volume of 5.00 L at 300. K. If the temperature is doubled under constant pressure, what will the new volume of the gas be?
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Gay-Lussac’s Law: Temperature & Pressure
Joseph-Luis Gay-Lussac(1778 – 1850)
Volume must be constantTEMP MUST BE KELVIN
As Temperature Increases, Pressure IncreasesP/T = k (a constant)P1/T1 = P1/T2
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A 10.0 L sample of gas in a rigid container at 1.00 atm and 200. K is heated to 800. K. Assuming that the volume remains constant, what is the new pressure of the gas?
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The Combined Gas LawPuts all three gas laws together.Any variable being held constant, can be
ignored.
On Reference Table T!
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A 2.00 L sample of gas at STP is heated to 500. K and compressed to 200. kPa. What is the new volume of the gas?
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A 2.00 L sample of gas at 1.00 atm and 300. K is heated to 500.K and compressed to a volume of 1.00 L. What is the new pressure of the gas?
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A 2.00 L sample of gas at 300. K and a pressure of 80.0 kPa is placed into a 1.00 L container at a pressure of 240. kPa. What is the new temperature of the gas?
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The Ideal Gas LawRelates the number of moles of a gas to
it’s pressure, volume and temperature:
NOT on your Reference Tables (MEMORIZE!)
Comes from the observation that 1 mole of any gas occupies a volume of 22.4L at STP.
PV = nRTn = # of molesR = Gas constant
‘R’, You say?!?Don’t get too twisted up about R. Its value depends on its units.
R = 0.082 atm L/mol KelvinHow did I get that?
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What is the pressure exerted by 3.00 moles of gas at a temperature of 300. K in a 4.00 L container?
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What is the volume of a sample of gas if 5.00 moles if it exerts a pressure of 0.500 atm at 200. K?
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A sample of gas is contained in a cylinder with a volume of 10.0 L. At what temperature will 2.50 moles of contained gas exert 20.0 atm of pressure on the container?
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A sample of gas contained in a cylinder of 5.00 L exerts a pressure of 3.00 atm at 300. K. How many moles of gas are trapped in the cylinder?
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Other Versions of “R”• Use the knowledge that 1 mole of any
gas occupies a volume of 22.4L at STP to derive R, if necessary.
• Determine the value of R in atm-mL/mol-K.
• Determine the value of R in kPa-L/mol-K.
