Chemistry SM-1232Week 1 Lesson

Dr. Jesse ReichAssistant Professor of Chemistry

Massachusetts Maritime AcademyFall 2008

Class Today• Champs get praise chumps get called out• Practice Conversions• Assumptions and properties • Simulator• Pressure• Pressure Units• Boyle’s Law: Pressure and Volume• Charles’s Law: Volume and Temperature• Practice Problems

Champs and Chumps

• If you are new stand up!

Champs and Chumps

• If you are new and see your handle on the list remain standing

Champs

• If you are standing you are a champ

Chumps

• If you had to sit down you’re a chump

Chumps

• Look at the people standing up, seek them out, and politely ask them for help so that you can be a champ instead of a chump

4 Assumptions

• What are the 4 assumptions that we make in Kinetic Molecular Theory to describe how gas particles behave?

4 Assumptions

• 1. Gas is a collection of particles in constant motion

• 2. Gas particles don’t attract or repel each other.

• 3. There is a lot of space between gas particles• 4. Temp determines kinetic energy

3 Properties of Gases

• What are the three properties of gases that separate them from solids or liquids?

3 Properties

• 1. Compressible• 2. Assume the shape and volume of their

container• 3. have low densities

Simulator

• Open the wiki• Click on Week 1 where you found these

lectures notes• You’ll notice a link• Click on the link and go to the page

Simulator Questions

• Write the answers down to the questions on this page and the next. Do it in pairs or by yourself.

• 1. What are the different variables that you can play with?

• What happens when you increase n?• What happens when you increase t?• What happens when you increase P?• What does the blue bar at the top represent?

Simulator Questions

• There is a button that says “keep pressure constant.” Click it.

• What happens when you increase n?• What happens when you increase t?• What happens when you increase v?

Last Simulator Questions

• How are P and V related?• How are P and T related?• How are V and T related?• How are V and P related?

• For example when X increases Y decreases or when P decreases Q increases

Definitions

• Pressure: Force / Area• Volume the amount of space something takes

up• Temperature: the amount of stored heat• N= the number of atoms (moles) in the system

Pressure

• Pressure = Force area• The force increases as more atoms are

introduced. The force decreases as atoms leave the system.

• If the force increases what happens to the pressure?

Pressure you feel• Every day of your life the air above you pushes down

on top of you. There is always pressure. • If you fly in an airplane you’ll notice a lot of babies

crying during take off and landing. You’ll also notice your ears prolly hurt a little. As you go higher there are few molecules of air pushing down on you, the pressure drops, and the imbalance left in your ear for a bit hurts.

• Deep sea divers also experience pressure, but since water is more dense than air they feel a heck of a lot more pressure on them.

Pressure Values

• The amount of pressure you feel on a daily basis at sea level from the force of the atmosphere on you we call 1 atmosphere of pressure.

mmHg aka Torr• Now, if you take a giant test tube, and pull a perfect

vacuum in it. Then you put it in a dish of mercury (Hg, the stuff in old thermometers) what you’ll find is that no matter how long the test tube is, you can only ever bring it up 29.92 inches or 760 mm.

• Chemists treat 1 atm, 29.92 inches of Hg, and 760 mmHg all as different ways of saying the same thing. Chemists also refer to mmHg units as “Torr” after Evangelista Torricelli who invented the barometer.

Pressure and Physics

• Typically when physicists are working they like the unit called a Newton. It describes a force. If you divide that force by 1 meter squared you have a force divided by an area. The resulting pressure is called a Pascal (Pa) and it’s pretty small. It’s so small in fact that you need 101,325 Pa to make 1 atm of pressure.

Americans• Americans don’t typically use the metric aka SI unit

system. They like pounds instead of kg and inches instead of centimeters… So, Americans have their own system of measuring pressure called a psi or pound per square inch.

• The pound is a force downward, the per means divide by, and the square inch is an area. Remember, Pressure = Force /Area.

• 1 atm = 14.7 psi. These are the units I used in grad school when I was doing pressurized reactions.

Conversion table• 1 atm = • 101, 325 Pa• 101.325 kPa• 760 mm Hg• 760 Torr• 14.7 psi• 29.92 in. Hg• Convert 12.3 atm into each unit. Write the

conversion factor down as you solve these.

Boyle

• When you looked at the simulation you should have found that when you increase Pressure you decrease volume. When you increase volume you decrease pressure. The first person to recognize this relationship was Robert Boyle, and so the law get’s called Boyle’s Law. We call this an inverse relationship cause they move in opposite directions.

Force on the walls

• Pressure is the net force of all the little gas particles hitting the wall of the container. If you force all those particles into a smaller space you’d get more and more collisions against the wall. That’s why the pressure goes up!

Boyle’s Law

• Chemists typically refer to the following equation as Boyle’s Law

• P1V1=P.2V2• Let’s see how it works.

Algebra

• Solve Boyle’s law for P1, and then start over and solve it for V2.

Boyle’s Law

• Set P1 and P2 to 15 atm, and V1 to 3L. What’s V2?

Boyle’s Law

• Using Boyle’s Law P1V1=P2V2, set P1 to 15 atm, P2 to 10 atm, V1 to 3L, determine V2?

• Did the pressure increase or decrease from P1 to P2?

• What happened to the volume?• Does that make sense knowing what we do

from Boyle’s Law?

To Do

• Chumps need to sign up for the wiki• Read 373 – 381• Copy your notes over• Quiz on 11 in one week (this coming Friday).

10 bonus points.• HW problems due March 6. Complete 1 HW

set for up to 3 people. 15 bonus points.• HW problems listed on the syllabus.