3: Unit Kinetic Theory, Gas Laws, Phases of Matter
Brent Royuk Sci-202 Concordia University
Kinetic Theory
If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms--little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied. Richard Feynman
Kinetic Theory
Some elements of the model 1.
Ideas of the Greek Atomists
Atomos: Greek for "uncuttable" The big three natural philosopher atomists Leucippus of Miletus ca 440 BC Democritus (ca 460-371 BC) of Abdera Epicurus (341-270 BC) of Samos Five chief points 1. All matter is composed of atoms, which are bits of matter too small to be seen. These atoms CANNOT be further split into smaller portions.
Epicurus: "Therefore, we must not only do away with division into smaller and smaller parts to infinity, in order that we may not make all things weak, and so in the composition of aggregate bodies be compelled to crush and squander the things that exist into the non-existent...."
Matter is made of tiny particles (atomic-molecular theory).
Is this a theory? Isn't it a law? The atoms of antiquity (see below)
2.
The particles are in constant motion.
How do we know this? Brownian Motion.
3. 4. 5.
In a gas, collisions with container walls produce pressure effects. Temperature depends on average speed of particles. Hotter = Faster All collisions are elastic.
2. 3. 4. 5.
There is a void, which is empty space between atoms. Atoms are completely solid. Atoms are homogeneous, with no internal structure. Atoms are different in size, shape, and weight. Philosophical atomism (materialism)
"Nothing exists except atoms and empty space; everything else is opinion." Diogenes Laertius
Matter Visualization
What does a gas look like, according to this model? The speed distribution curve
Matter Visualization
Gas in a Balloon applet What features of the model explain the distinguishing characteristics of liquids and solids? A classroom simulation?
1
Examples
1. 2. 3. Molecules in Motion applet Kinetic Simulation Theory applet The gas laws (hotter = more pressure; hotter = more volume) The Ideal Gas Law applet Heating closed containers can cause explosions Objects expand when heated sidewalk joints Gas Properties: Expansion, Diffusion Diffusion applet Diffusion-Limited Aggregation Fractal Some hot water faucets turn themselves off (only once) The valve on a bicycle tire gets hot when you pump it up, but not if you use a pressure hose.
Phase Changes
4. 5. 6.
7. 8.
Phase Changes
1.
1. To change from liquid to gas, particles take along some "extra" motion boiling temp maxes out 2. A gas-liquid equilibrium Evaporation applet 3. Boiling is pressure dependent: why? high altitude instructions pressure cookers boil test tube with ice cube 4. Moth Balls demo heating curve for water: 80/540 Fusion graph
Modeling Phase Changes
Observation: it takes a lot of "heat" to melt things or vaporize things- boiling temperature, mothballs freezing Law: Phase changes require heat. Models Particle model: "Red Rover", springs Energy model: it takes extra heat energy to effect a phase change What about melting and condensation?
2. 3.
The Caloric Model
What was it? What was wrong with it?
Count Rumford Munich, 1798
The Caloric Model
In 1798, Count Rumford published An Experimental Enquiry Concerning the Source of the Heat which is Excited by Friction, a report on his investigation of the heat produced while manufacturing cannons. He had found that boring a cannon repeated...