boyles law models

Looking at Boyle’s Law: 

Looking at Boyle’s Law Developing models that makes sense for the behavior of gas volume as pressure changes

Looking at Boyle’s Law: 

Looking at Boyle’s Law Developing model that makes sense for the behavior of gas volume as pressure changes “How is the gas pushing back?”

Objectives: 

Objectives Students will compare two possible models for the behavior of gases in the prior experiment. They will learn how to solve problems involving pressure and volume of a sealed gas at constant Temperature.

A Coincidence?: 

A Coincidence? Look at your experimental results Compare behavior of all gases at the same temperature, all of the gases we studied had the same behavior. If we started out with 25.0 ml of oxygen or 25.0 ml of methane, the addition of one, two, three or four books, within experimental uncertainty, gave us the same volumes and thus the same graph. Further studies would show that all gases, no matter their density, have the same compressibility!

Boyle's Law: 

Boyle's Law For all gases , as pressure increases, volume decreases in the same way!

Score in the Gas Density Contest: Bigger particles 1 More particles 0: 

Score in the Gas Density Contest: Bigger particles 1 More particles 0 More Particles More Mass

What is Happening?: 

What is Happening? We need to come up with a model of what is going on inside the syringe with these gases. Empirical (Experimental) model: an imagined system that would explain the empirical observations A really good model not only explains, it also predicts A good model comes with a formula. The math helps us understand how the system works. The math helps us make predictions, too.

An Infantile Model: 

An Infantile Model Even small children make models of their world, intuitively How does this TV work? “There are people inside the TV” Model makes sense of some data But when a landscape comes up. . . Baby begins to understand that the model does not explain all the data Cars & big animals don’t fit People are “scaled” to all sizes Model is revised. . . The cable brings pictures like a waterpipe !

Refining the model: 

Refining the model The TV waterpipe model The waterpipe model is an improvement It denies that there are people in the TV It explains how so much information gets into the TV It explains why the TV goes off when the cable is “down” But it doesn’t explain how the picture gets onto the viewing screen

Additional Refinements: 

Additional Refinements Raster imaging The child looks closely at the screen He notices that the image is made up of dots of various colors, laid down in horizontal lines He looks up the topic on the Internet or in a book and finds that electron “guns” fire electrons at the phosphorescent screen, moving rapidly across the screen to lay down the screen images This process is called raster imaging But the child still has more work to do before he can “build” a TV screen

Modeling P-V behavior: 

Modeling P-V behavior Can we construct a physical model that makes sense? Model 1: A model that explains how it is that an increase in pressure is accompanied by a reduction in volume of a gas A model that makes sense in terms of a common physical system, easily visualized A model that approximates the data mathematically, within certain limits

Yes, the one and only: 

Yes, the one and only A Viacom trademark

The Sponge Model: 

The Sponge Model Does it explain pressure-volume behavior? Within limits, it does

The Sponge Model: 

The Sponge Model Does it explain pressure-volume behavior? Within limits, it does As you increase pressure, the volume goes down

The Sponge Model: 

The Sponge Model Does it explain pressure-volume behavior? Within limits, it does As you increase pressure, the volume goes down When you reduce the pressure, the volume goes up

The Sponge Model: 

The Sponge Model Does it explain pressure-volume behavior? Within limits, it does As you increase pressure, the volume goes down When you reduce the pressure, the volume goes up As the volume gets very small, resistance to further compression gets very large It could explain density variations in gases However. . . A Viacom trademark

The Sponge Model: 

The Sponge Model Where it falls short Outside limits The sponge will not expand into any volume as a gas will when pressure gets really small The sponge takes up a finite volume beyond which it cannot be compressed After a period of time, the sponge collapses under pressure The sponge is visible; gases, unless they absorb light, cannot be seen

Disclaimer: 

Disclaimer CHICAGO — The cartoon character SpongeBob SquarePants is in hot water from a study suggesting that watching just nine minutes of that program can cause short-term attention and learning problems in 4-year-olds. The problems were seen in a study of 60 children randomly assigned to watch either “SpongeBob SquarePants” or the slower-paced PBS cartoon “Caillou” or assigned to draw pictures. Immediately after these nine-minute assignments, the children took mental function tests; those who had watched “SpongeBob” did measurably worse than the others.

Kinetic Molecular Theory: 

Kinetic Molecular Theory Let’s consider this as an improved model KMT Says that gases are made up of small particles, called molecules Quite invisible and in constant, rapid, random motion, never slowing down as long as the temperature stays the same They collide with the walls of the container, imparting force and thus showing a pressure

Change Pressure: 

Change Pressure Push in the plunger Molecules don’t move faster but collide more frequently as walls get closer together; pressure increases and volume decreases Frequency of collisions and pressure should double as volume is cut in half So if P 1 = 1 unit and V 1 = 1 unit, we would expect when P 2 = 2 units, that V 2 would be ½ unit

Assumptions: 

Assumptions Or it won’t work Assume in kinetic molecular theory Somehow the gas molecules on the whole are not slowing down Or else the piston would gradually collapse We suspect that the constant temperature has something to do with this, but will look at that in later experiments. If no energy is being lost in the collisions, the physicists tell us that these collisions are perfectly elastic. Like billiard balls clicking

One More Note: 

One More Note A practical application of Boyle’s Law When you breathe Your diaphragm muscles relax, pulling down on your chest cavity & reducing the pressure inside That makes the lungs expand (P↓makes V↑) so pressure in lungs is less than atmospheric Higher atmospheric pressure pushes air into the lungs When your diaphragm muscles push up, that increases pressure in the lungs to slightly above atmospheric, and “exhaust” air flows out

Can we “prove” that there are gas particles, and that differences in density are caused by different sized particles?: 

Can we “prove” that there are gas particles, and that differences in density are caused by different sized particles? Yes, and in 1811, using the work of other scientists, Amadeo Avogadro showed us how to count particles we can't see, using the chemical reactions of gases at the same temperature & pressure