Phase class #2OB: Describing gases with the kinetic molecular theory of gases, detailing

how barometers work, and then, lots of pressure unit conversion math

YouYour dog:

Pressure Unit Conversion

Math

AKA: PUC

This theory explains how gases “work”. How they exist as gases, how they stay gases, how the particles of gas act (atoms or molecules), and how we understand gases in our minds.

Depending how you count the concepts, there are seven points to ponder…

The kinetic molecular theory of gases states that gases

1. Are made up of small particles such as atoms or molecules

2. And that these particles will act as if they are small, hard spheres. They aren’t really, they do have shapes, and are not spheres, but they act as if this is true.

The kinetic molecular theory of gases states that gases

1. Are made up of small particles such as atoms or molecules

2. And that these particles will act as if they are small, hard spheres. They aren’t really, they do have shapes, and are not spheres, but they act as if this is true.

3. They have no attraction for or any repulsion for any other gas particles. This is not true either, but the attraction and repulsion they have for one another is small, and unless crazy cold, no real effect on gases.

4. The particles move very fast, and only in straight lines. It’s very geometric, no spiraling particles.

The kinetic molecular theory of gases states that gases 1. Are made up of small particles such as atoms or molecules

2. And that these particles will act as if they are small, hard spheres. They aren’t really, they do have shapes, and are not spheres, but they act as if this is true.

3. They have no attraction for or any repulsion for any other gas particles. This is not true either, but the attraction and repulsion they have for one another is small, and unless crazy cold, no real effect on gases.

4. The particles move very fast, and only in straight lines. It’s very geometric, no spiraling

particles.

5. All collisions are elastic: when the gas particles hit each other all of their energy is transferred, none is lost. This is not true, but the loss of energy is small, and the addition of energy all the time from the Sun, and the Earth more than makes up for it. Gases do stay gases usually.

6. Collisions result in pressures being exerted. The more collisions the higher the pressure. The stronger the collisions, the higher the gas pressure too.

The kinetic molecular theory of gases states that gases 1. Are made up of small particles such as atoms or molecules

2. And that these particles will act as if they are small, hard spheres. They aren’t really, they do have shapes, and are not spheres, but they act as if this is true.

3. They have no attraction for or any repulsion for any other gas particles. This is not true either, but the attraction and repulsion they have for one another is small, and unless crazy cold, no real effect on gases.

4. The particles move very fast, and only in straight lines. It’s very geometric, no spiraling particles.

5. All collisions are elastic: when the gas particles hit each other all of their energy is transferred, none is lost. This is not true, but the loss of energy is small, and the addition of energy all the time from the Sun, and the Earth more than makes up for it. Gases do stay gases usually.

6. Collisions result in pressures being exerted. The more collisions the higher the pressure. The stronger the collisions, the higher the gas pressure too.

7. Particles are separated by vast distances from each other relative to the size of the particles. Gases are mostly empty space, and particle size is insignificant. The particles do take up some space, but it’s tiny. In theory, the particles act as if they take up no space at all, but that’s silly.

Gas pressure was originally measured in pounds per square inch because a bunch of smart guys, who came from Europe, where they used pounds for measuring, and who happened to invent the barometer, decided things.

So a bunch of these science guys go on a long round the world road trip, with a barometer (so they could say they were working!), and they measured how high up the mercury went near the oceans, up the mountains, in the hills, in cities, towns, caves, etc.

They decided amongst themselves what “normal” was. The decision was that

When the mercury rose up to 760. mm in height in the vacuum tube, the air pushing it that much was “normal” pressure.

The rest is just math conversions, different instruments, and more math. Easy but we’ll practice some now.

Evangelista Torricelli, circa 1640, father of the Torricelli Tube, or the early mercury air barometer.

(1 Torr is about 1 mm Hg)

Gas pressure conversion practice problems…

Today it’s a higher pressure day (cold air is denser than warm), so the pressure outside is about 825 mm Hg. Convert that to atmospheres and then to kilopascals.

Gas pressure conversion practice problems…

Today it’s a higher pressure day (cold air is denser than warm), so the pressure outside is about 825 mm Hg. Convert that to atmospheres and then to kilopascals.

825 mm Hg1

X = 1.09 atm 1.0 atm760. mm

Hg

825 mm Hg1

X = 110. kPa 101.3 kPa760. mm Hg

In Boulder, Colorado, where my mean sister in law Donna lives, the air pressure is much lower than Vestal. That’s because she’s so high in the mountains, there is less air pressing on them than at lower altitudes like here.

Air pressure in Boulder the other day was just 644 mm Hg. You’d be light headed probably. Convert that to atm and to kPa.

In Boulder, Colorado, where my mean sister in law Donna lives, the air pressure is much lower than Vestal. That’s because she’s so high in the mountains, there is less air pressing on them than at lower altitudes like here.

Air pressure in Boulder the other day was just 644 mm Hg. You’d be light headed probably. Convert that to kPa and to atm.

644 mm Hg1

X = 85.8 kPa 101.3 kPa760. mm Hg

644 mm Hg1

X = 0.847 atm1.0 atm760. mm

Hg

Convert 40.0 kPa into mm Hg and then into atm.

Convert 40.0 kPa into mm Hg and then into atm.

40.0 kPa1 X = 300. mm Hg760 mm Hg

101.3 kPa

40.0 kPa1 X = 0.395 atm1.0 atm

101.3 kPa

Last set, convert 2.55 atm into kilopascals and then into mm Hg

Last set, convert 2.55 atm into kilopascals and then into mm Hg

2.55 atm1

X = 258 kPa 101.3 kPa1.0 atm

2.55 atm1

X = 1938 kPa 760 mm Hg

1.0 atm

1940 kPa with 3SF