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Phase Changes - Physical Science

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Mr. S. Soderholm

on 31 January 2014

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Transcript of Phase Changes - Physical Science

Your Cartoons
The assignment:
Colder than Solid?!
Bose-Einstein condensates form within about 100 nK of absolute zero. Yes, that's nanokelvins. Several atoms begin behaving in many ways as if they were only one particle. Here's a video on them...
Superconductors and superfluids exhibit strange behavior, but require quite low temperatures (under 100 K).
"Quark-gluon plasmas" are much more rare, and occur when the quarks that make up protons and neutrons actually come apart. This requires incredible amounts of energy. These guys say it's really a sort of liquid:
Hotter than Gas!
Plasmas are gases at high enough temperature that some electrons are free of the atoms. Plasmas conduct electricity and give off light as electrons are recaptured by ions. Fluorescent lights, lightning, and the spark you see when you close a car door in the winter are all plasmas.
Heating and Cooling Curves
Phase Changes
KMT Description:
The particles are vibrating in place (not motionless, and not moving past each other).
occurs at lower temperatures, but sometimes higher pressures can also produce solids.
Crystalline vs. Amorphous solids
The solid shown in the background is crystalline, with a regular ordered arrangement of particles. (ex: quartz)
Amorphous solids occur when the particles are disordered or jumbled (ex: glass)
KMT Description:
Particles remain close together, but are able to move past each other.
A liquid will therefore take the shape of its container.
strange liquids:
liquid crystals are liquids whose molecules are aligned in a crystalline way.
Some liquid crystal molecules can be controlled with electric current. They also happen to twist polarized light, and make LCD's possible.
Ideal Gases +
Gas Laws

proportionalities (gas laws)
Phase Diagrams
KMT Description:
Particles are far apart from each other, moving completely independently of each other.
Therefore, a gas will take the shape and volume of its container.
High temperatures and/or low pressures cause substances to be gaseous.

Supercritical Fluid
KMT description:
particles remain close together, but can move past each other and can expand to fill their container.
Properties of both a liquid and a gas - can't really say which it is.
Only occurs at high temperatures and pressures
SF6 being heated in a small container.
It starts boiling, but when the pressure gets too high, it becomes a supercritical fluid
(liquid-gas boundary disappears.)
When the temperature is reduced, the two phases return.
The motion of molecules explains many phenomena.
The molecules making up matter are always in motion.
Matter is made up of tiny individual particles (molecules) not continuous "stuff."
Kinetic Molecular

Ideal Gas:
molecules have zero volume (or are so far apart their volume is negligible)
molecules experience zero intermolecular forces (or have so much kinetic energy and such weak intermolecular forces they're negligible)
Graham's Law
distribution of KE
Water (H2O)
carbon dioxide (CO2)
Dalton's Law
Boyle's Law
of partial pressures
Charles's Law
Absolute Zero
All molecular motion ceases.
An ideal gas would have zero
volume and pressure.
Pressure is inversely proportional to volume.
Temperature is directly prportional to pressure.
Temperature is directly prportional to volume.
volume is directly proportional to moles of gas.
V n
P 1/V
Gay-Loussac's Law
Avogadro's Law
(Avogadro's Hypothesis)
Avogadro's experimental evidence:
Gases react in simple, whole-number volume ratios.
For ideal gases, the ratio(P*V)/(n*T) will be constant under all conditions. The constant value is called
the ideal gas constant!
which for some reason is abbreviated "R"
R = 0.0821 (L*atm)/(mol*K)
To make it easier on the eyes (and enjoyably pronouncable!) the relationship of P, V, n, and T to R is given as
KMT Cartoons Quiz
Fri. 3/11
12 items on molecules' actions and relationships among P, T, V, n
291 K or 18 C
a solid can change in temperature as its molecules vibrate in place faster or slower.
a liquid can change in temperature as its molecules move around each other faster or slower.
a gas can change in temperature as its molecules move independently from each other faster or slower.
In an equilibrium mixture of solid and liquid (melting or freezing) the (potential) energy absorbed by bond breaking or released by bond formation will keep the temperature constant even if it's different from the surroundings' temperature.
In an equilibrium mixture of liquid and gas (boiling, evaporating or condensing) the (potential) energy absorbed by bond breaking or released by bond formation will keep the temperature constant even if it's different from the surroundings' temperature.
calculating energy changes: beyond the Honors Chem. curriculum, but stay tuned next year for more!
Heating Curve
What's going on here -
Why does the temp. drop below freezing without freezing?
Why does the temp. increase suddenly when freezing starts?
Supercooling -
freezing may not happen without a "condensation nucleus" like a scratch in the container or a "seed crystal" of solid.
The temp. jumps up because of bond formation, which releases energy. PE decreases, but KE increases to the freezing point.
Dew Point
When you perspire, your body puts liquid water on your skin's surface so it can evaporate.
As the water evaporates, it absorbs energy and cools your body.
If the humidity is too high, the water doesn't evaporate effectively and you don't cool down.
Unless, of course, you "glisten"
The "dew point" on a weather forecast gives you a prediction of that night's lowest possible temperature.
At the dew point, water vapor will begin condensing as dew on the ground.
As the water condenses, it releases energy. This keeps the temperature from falling any lower than the dew point.
During cooling, thermal energy is always decreasing
(combination of PE and KE, or the total of the ordered and disordered collisions)
During heating, thermal energy is always increasing. (combination of PE and KE, or the total of the ordered and disordered collisions)
weighing by redox lab
Vacuum Pump
"Inflationary Pressure"
The air molecules inside and outside the balloon initially are colliding with tthe same force, so the balloon does not expand or contract.
When the outside air is removed, there is very little force of colliding molecules to oppose the molecules colliding on the inside
The imbalance of pressure causes the balloon to expand.
"The Amazing Expanding Peep
of Montgomery County"
when the surrounding air is removed, the molecular collisions with the insides of the air bubbles are able to push the walls back, making the marshmallow expand.
Many of the air bubbles pop, releasing the air inside, so when atmospheric pressure is returned outside, the peep is crushed
"More than one way to boil water"
We connected a flask of ice water to the vacuum pump and it boiled!
Removing the air pressure makes it much easier for liquid molecules to boil - now they only have to break their intermolecular forces, not also push against air pressure.
This video shows another way to get to the "triple point" of a substance. Boiling the liquid in a vacuum cools it as boiling absorbs energy from the liquid. Eventually, the temperature drops enough that the boiling liquid freezes!
Group A:
Phases of matter
Phase changes
Charles' Law
Group B:
Boyle's Law
Gay-Lussac's Law
Dalton's Law
Group C:
Ideal Gases
Graham's Law
Avogadro's Hypothesis
Molar volume of an ideal gas
Review Sheet
Investigate The effects of temperature and mass on average molecular speed in the PhET "gas properties" simulation...
Ice water
As ice melts, the temperature of the ice/water mixture remains constant.
at zero Celcius, the ice begins to melt.
as the water molecules separate, hydrogen bonds are partially broken.
the breaking of bonds absorbs energy, keeping the water molecules from speeding up. The mixture remains at zero Celcius until the ice is gone.
Steam at 100 celcius is more dangerous than liquid water at 100 celcius.
liquid water transfers energy to you as it cools. It hurts.
steam (gaseous water) releases more energy as it becomes a liquid. As the molecules form hydrogen bonds between them, a great deal of energy is released. That hurts more!
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