1. Intro. to Chemistry:
Gas Laws 1

2. Mission Possible
The recent Odyssey probe to mars has sent back a sample of the Martian surface, called Oobleck. Your job is to determine if it is a solid, liquid or gas.
As a group, decide what criteria you’ll use to make the decision using Yes/No questions. Test the Oobleck and then report your results to me.
Your report must explain the tests you did, their results, and justification for your decision. . . 2

3. Thermal energy vs. Temperature
Temperature measures the speed of the particles. (kinetic energy)
Thermal energy measures the total energy in the substance. (includes vibrational and kinetic energy)
A boiling cup of tea at 100°C will have a higher temperature than a swimming pool at 25°C, but the tea has less thermal energy.
A pool has more matter with vibrational (unused) energy, but that matter is moving slower.
A slow moving train can hold more than a fast moving car. 3

4. Thermal Expansion and Kinetic Theory
Objects expand when heated.
Expansion joints, thermometers and hot air balloons.
When the temperature is increased molecules move / vibrate faster and vice versa.
Water is the exception to the rule.
Water molecules lock themselves together with empty spaces between them. 4

5. Amorphous Solids
Some materials do not have a distinct melting point, but melt over a range of temperatures.
Called Amorphous solids
Examples:
Butter
Glass 5

6. Pressure Amount of force per area.
Pressure = F/A
If you increase the area, you reduce the pressure.
Unit is Pascal (Pa)
1 Pascal is very small, so normally given as kilopascal (kPa)
Atmospheric Pressure is kPa 6

7. Pressure Examples 7

8. Air Pressure Kinetic Theory states particles are in constant motion.
At some point they’ll collide with the container’s edge.
Air pressure is due to gas particles colliding with container. 8

9. Boyle’s Law (1662) As volume decreases; the pressure increases.
Inverse (opposite) relationship.
Only valid if temperature is constant.
P1V1 = P2V2
Pressure increase due to more collisions per time.
Filling up a smaller balloon with the same amount of gas as a big balloon. 9

10. Boyle’s Law Practice #1
A balloon has a volume of 10.0 L at a pressure of 101 kPa. What will be the new volume when the pressure drops to 43 kPa?
Known:
Unknown:
Formula:
Solve: 10

11. Boyle’s Law Practice #2
A volume of helium occupies 11.0 L at 98.0 kPa. What is the new pressure if the volume is reduced to 5.0 L?
Known:
Unknown:
Formula:
Solve: 11

12. Charles’s Law (1787) As temperature increases; volume increase.
Proportional (same way) relationship.
Only valid if pressure is constant.
T1 / V1 =T2 / V2.
As temperature increases, the particles travel faster and can cover more ground.
Examples:
Basketball
Bread Dough 12

13. Absolute Zero
The lines for all gases seem to point to a common point when plotting Temperature vs. Volume.
Common y-intercept at -273°C.
Volume at would theoretically be zero on the graph which is not possible.
Temperature called absolute zero – nothing colder.
All particle motion stops! 13

14. Kelvin Scale Set -273°C equal to 0 Kelvin.
Add 273 to any Celsius temperature to get Kelvin.
To do Charles’s Law calculations, temperature must be in Kelvin.
Bonus Question: Which scale makes the most sense? Which one do we use? 14

15. Charles’s Law Practice #1
A gas at 300K has a volume of 2.0L what is the new volume if the gas is cooled to 273 K?
Known:
Unknown:
Formula:
Solve: 15

16. Charles’s Law Practice #2
A gas bubble in bread dough at 20°C has a volume of 20mL. What is the volume of the bubble when the dough is cooked in to bread at 125°C?
Known:
Unknown:
Formula:
Solve:

17. Temperature – Pressure Relationship
If the container’s volume is kept constant; the pressure will increase as the temperature increases.
Particles are traveling faster, so they hit the container with more force.
Examples:
Aerosol Can
Tire pressure in the winter

18. Now let’s do a Gas Laws Simulation…18