Gas and Pressure

Review Kinetic Vs. Potential Energy

Kinetic Molecular Theory

Explains the behavior of gases

Real gases– do not follow all the assumptions of this theory.

Theoretical, applies to an ideal gas Gas following all the assumptions of the theory.

Kinetic Molecular Theory

1) Gases are made up of TONS of particles, constantly moving, and spread out.

2) Gas particles drive straight until they hit/collide with something (ex. Wall, particles).

3) Small particles, HUGE space for them to roam! Gas volume mainly empty space

Kinetic Molecular Theory (cont.)

4) No force of attraction! –gas particles randomly move around

5) When gas particles collide with each other or a container wall, no kinetic energy is lost when they collide.

6) Temperature determines average kinetic energy of gas particles.

-not all gas particles are moving at the same kinetic energy

Properties of Gases

1) Expandable No shape No defined volume Fills whatever container is available to it. Move quickly and no attraction

2) Fluid Gases move similar to liquids No attraction to worry about

3) Low Density Least dense state of matter for most substances Due to distance between particles

Properties of Gases (cont.)

4) Diffusion Gas particles mix with each other and disperse “Spontaneous mixing of gas particles from 2 substances

due to random motion” (ex. Perfume)

5) Effusion Describes gas movement through a small opening. (ex.

Tire puncture) Related to how fast gas particles can move.

6) Compressibility Gas particles are able to be packed close together. Decreased volume

Pressure

“force per unit area on a surface”

Gas particles colliding against container and creating force Force a gas exerts on its surroundings

Unit = Newton (N)

Amount of pressure dependent on Volume, Temperature, and particle/molecule number.

Ex. Atmospheric pressure

How do we measure pressure?

Barometer– atmospheric pressure

Evangelista Torricelli (1600s) Mercury falls to 760 mm Air pressure holds 760 mm mercury column.

Barometer The pressure of the

atmosphere at sea level will hold a column of mercury 760 mm Hg.

1 atm = 760 mm Hg1 atm Pressure

760 mm Hg

Vacuum

Pressure Units

Common: mmHg (millimeters of Hg)

Measurements done in “atmosphere units”

1 atmosphere of pressure (atm) = (sea level, 0° C) 760 mmHg 760 torr 1.01325 x 105 Pa 101.325 kPa

Example 1:

1.75 atm of pressure to mmHg

Example 2:

570 torr of pressure to atmospheres.

kPa?

Pressure Conversion Practice

1. The tire pressure for one tire on my car reads 0.9813 atm. Convert this pressure to mmHg.

2. 200 torr ---------------- kPa

3. The atmosphere supports a column of mercury at 670 mm in height. What is the atmospheric pressure in atm?

4. 15 Pa ------------------ atm

5. A weather report gives a current atmospheric pressure reading of 745.8 mmHg. Express this reading in kilopascals.

Homework

Post-Lab Questions

Study for Kinetics Quiz on Tuesday