Gas class #1 OBJECTIVE: understanding the nature of gases, the KMT, the 4 variables to measure gases, and the first demo diagram for gases.

3 rd Quarter !!! A Fresh Start. 15 minutes of hard work per day, doing problems, doing drills, or rewriting your notes. Active Studying - Reading is important, especially the BASICS, but DOING is really studying. Make a List of questions for your teacher. REALLY. Tomorrow I will hand out FLASH CARDS, which you must cut out and you must use. You are not a number in a box, but you can have any number you want. Just do the work you need to. Don’t look left and right, look within. Don’t compare yourselves to others, there will always be those greater or lesser than yourself. That does not matter. Being the best YOU is all that really counts. Never give up on yourselves, I never will. A fresh start can begin today.

During phases we covered gases a bit, but now we will truly examine them in more detail. The Kinetic Molecular Theory (KMT) explains them generally, and we need to be familiar with that. For review… The Kinetic Molecular Theory to explain gases 1Gases are in random, constant, straight line motion. This is TRUE, particles (atoms or molecules) only move straight, no curves or loops allowed. If gases slowed down, they’d clump up into liquids, which is not allowed if you want to be a gas.

The Kinetic Molecular Theory 2Gas particles are separated from each other by vast distances from each other, relative to their actual sizes. Imagine a small herd of bulls in a few acres of land. Although the bulls only take up a small amount of physical space, they control the whole area. Gas particles are crazy small, but their motion takes up a much larger space. Gases are in fact mostly empty space. Particle size is negligible compared to the real gas volume. 3 The particles of gas act as small hard spheres. They are not really hard (they are just surrounded by electrons, which are also mostly not there) but they do bang into each other a lot and bounce off each other too. They ACT like small, hard spheres, but they all have shape, and hardly any are actually spherical.

The Kinetic Molecular Theory 4 These gas particles (atoms or molecules) have no attraction or repulsion for each other. This is not really true, the gas atoms or molecules DO have some attraction for each other, and some repel each other, but this would lead to a decrease in the total kinetic energy of the gas, which would eventually slow the particles down enough that they would form into a liquid. This does not happen generally because the small loss of energy caused by the small but real attraction and repulsion is made up for by the Sun’s energy (for free, so to speak).

The Kinetic Molecular Theory 5 The collisions between the particles of a gas are ELASTIC. Gas particles transfer all of the energy back and forth, and they never losing their average Kinetic Energy This doesn’t really happen either, but it seems like it does. All of the gases that I know are gases and stay gases. If there was a loss of energy due to the collisions, the gases would literally slow down and turn into a liquid. There is some small, but measurable loss of energy, but that too is made up from the “free energy” provided by the Sun. Gas collisions result in PRESSURE being formed. More collisions or stronger collisions makes higher gas pressure. Less collisions or weaker collisions make for a lower gas pressure.

The Kinetic Molecular Theory 6Gases can be compressed indefinately but they remain gases and do NOT become liquids (or worse! Solids). This is also untrue. Real gases (all gases) can be compressed only so far before they become liquids. But gases in our real life appear to always remain gases. That’s because in our real life it doesn’t get so cold, or so high pressure that we see it happen. It happens, trust me. 7The average Kinetic Energy is directly proportional to the Kelvin Temperature of a gas. We never use any temperature scale other than Kelvin, no zeros or negative numbers are allowed into our formulas. Kinetic energy and temperature are like Michael Jackson’s Hand + Glove, they move together.

4 variables to measure gases… 1The pressure of a gas, using any units you know such as: kilo-Pascals kPa atmospheres atm millimeters of mercury mm Hg pounds per square inch psi 2The temperature of a gas, using only KELVIN Zero temperature means zero on only one scale. Normally chilly temperatures around here of 0°C or -5.5°C will create math problems with our formulas. Only Kelvin, OK (not absolute zero either!) 3The volume of a gas, using any units you know, probably though it will be in Liters, or milliliters. 4The number of moles of gas, (they’re back!)

Kinetic Energy + Temp. are DIRECTLY PROPORTIONAL Which means, as one changes, the other follows. If one variable here increases, so does the other. Kinetic Energy Temperature in Kelvin The line must be straight, the slope constant, but it does not have to be a 1:1 ratio (45 °angle).

Gas Demo Diagram #1 (on loose paper, to be collected with the rest of the diagrams) Title: Relationship between the Volume + Temperature of Gases HEAT water balloons ice

THINK, don’t write yet… Will the balloon in the cold water get Bigger or Smaller? Will the balloon in the hot water get Bigger or Smaller?

Cold will make the balloon smaller: why? The colder the gas particles, the lower their kinetic energy, making for weaker collisions and also fewer collisions. The balloon “collapses”. Lower temperature reduces volume. Hot will make the balloons expand, why? The hotter the gas particles, the greater their kinetic energy, the stronger the collisions and the more collisions will occur. The balloon expands. Higher temperature increases volume.

Volume + Temperature of a gas are DIRECTLY PROPORTIONAL Hotter temps mean bigger balloons. Lower temps mean smaller balloons. Temp as a Function of Volume Volume as a Function of Temp volume temp volume

Back to Notes… Draw small graphs in your notes. 1. Gas Temp as function of Volume 2.Gas volume as function of Temp 1 2 Finish this statement: Gas temperature + Volume are ___________ __________

Directly proportional DOES NOT MEAN that the graph has a slope of 1. ANY straight line graph is directly proportional (like all of these) Tonight… Gas HW #1 to be collected tomorrow.