1. The Nature of Gases

2. Gases Occupy Space
All matter, including gases, have mass and occupy space
Balloon in a bottle demo
The first concept of gases that we are going to explore is that gases occupy space. Gases are a form of matter and all matter have mass and occupy space. Remember that a gas can expand to fill its container, unlike a solid or liquid. Gases can also be easily compressed or squeezed into a smaller volume under pressure. So why can gases be compressed more easily than liquids or solids? Because there is more space between particles in a gas. At ordinary pressures, the distance between individual particles is of the order of ten times the diameter of the particles. At that distance, any attractions between the particles are fairly negligible at ordinary temperatures and pressures.

3. Balloon in a Bottle Reasoning
The air/gas in the bottle is compressed.
The compressed air exerts more pressure on the balloon than you can blow into it.

4. Kinetic Theory
Tiny particles in all forms of matter are in constant motion
Kinetic Theory states that all particles of matter are in constant motion, and we can confirm this with gases because we know that odors travel. The average speed of an oxygen molecule at 20C is 1700 km/h. Using this fact, we can calculate that the odor of a cheese pizza could go from DC to Mexico City in 115 min, that is if there was no other matter interrupting the oxygen molecule’s travel.

5. Kinetic Theory
Particles in motion exert forces when they collide with other bodies
Gas pressure is the result of simultaneous collision of tons of gas particles with an object
Particles increase their motion with greater temperature
So we know that gas particles are in constant motion, so how does that relate to the behavior of gases? Well when gas particles move about they collide with other particles and objects. If one gas particle collides with another with enough energy
Explain the reason why some collisions are effective and some are ineffective. Identify the reactants and products.

7. Balloon Demonstration Part 2
Explain the process of blowing up the balloon in terms of gas particles?

8. Balloon Demonstration Part 2
Gas (Carbon Dioxide) from the lungs is blown into the balloon
You are increasing the number of gas particles in the balloon

9. Balloon Demonstration Part 3
Explain why the balloon blows up using the kinetic theory

10. Balloon Demonstration Part 3
The gas particles are in constant motion and exert a force or pressure on the inside wall of the balloon causing it to expand

11. After Mini Experiment Record your results on your notes sheet
Answer the 2 analysis questions

12. Mini Experiment
Add small drops of BTB (bromothymol blue) to the small circles in the pattern shown on the template. Be sure the drops do not touch one another.
Mix 2-3 drops of each HCl and NaHSO3 in the center, large circle of the pattern.
Quickly place the Petri dish over the grid to enclose the reaction (this means solid side up).
Observe and record what happens in the data table for the reaction.
Wipe the template with a paper towel and throw away in the garbage.

13. Atmospheric Pressure
Air exerts pressure on Earth because gravity holds air molecules in Earth’s atmosphere
Atmospheric pressure refers to the collision of air molecules with objects

14. The air around you exerts pressure on your body all the time.
Atmospheric Pressure
The air around you exerts pressure on your body all the time.
As you climb a mountain, atmospheric pressure decreases

15. Atmospheric Pressure
If you have the same pressure both inside and outside (atmospheric pressure) of an object then the forces created by those objects are equal
The object will not be crushed or expanded

16. Mauna Kea
Hawaii’s tallest dormant volcano – 33,500 ft (10,200 m) from Pacific floor. World’s highest mountain island
Pressure differences – crush or expand

17. Pop Can Demo Procedure Fill a can with 10-12 mL of water
Fill a pan with cold water
Heat the can until water is boiling and steam is visible
Invert the can in the cold water making sure that the opening is completely submersed

18. The Collapsing Can What happened?
When you heated the can you caused the water in it to boil. The vapor from the boiling water pushed air out of the can. When the can was filled with water vapor, you cooled it suddenly by inverting it in water. Cooling the can caused the water vapor in the can to condense, creating a partial vacuum. The extremely low pressure of the partial vacuum inside the can made it possible for the pressure of the air outside the can to crush it.

19. When you heated the can you caused the water in it to boil
When you heated the can you caused the water in it to boil. The vapor from the boiling water pushed air out of the can. When the can was filled with water vapor, you cooled it suddenly by inverting it in water. Cooling the can caused the water vapor in the can to condense, creating a partial vacuum. The extremely low pressure of the partial vacuum inside the can made it possible for the pressure of the air outside the can to crush it.

20. The Collapsing Can Demonstrates:
The effect of atmospheric pressure (pressure of the gases in the air) on an object
The effect of temperature on a gas

21. Effect of Increasing Temperature on Gases
Heating the water in the can
Increasing the temperature of the liquid water causing the liquid to become water vapor
Increasing the temperature speeds up the particles
Increasing the speed means more collisions against the object
Increasing the pressure inside the object

22. Effect of Decreasing Temperature on Gases
What was the effect of putting the can in cold water?
Seals the top of the can
Decreasing the temperature decreases the speed of the gas particles
Gas particles condense
Causes a pressure difference between the atmosphere and inside the can

23. Standard Temperature 0ºC or 273K Celsius to Kelvin Kelvin to Celsius
ºC = Kelvin
Kelvin to Celsius
Kelvin = ºC

24. Standard Pressure 101.3 kPa (kilopascals) or 1atm Convert atm to kPax
G atm
101.3 kPa
1 atm x
G kPa

25. Pressure Continued
1 atm = 760 mmHg

26. Variables used to describe a gas
Pressure (kPa)
Volume (L)
Temperature (K)
n (number of moles)
**Our goal is to be able to predict the behavior of a gas given specific conditions

27. Review
Take some time to answer the practice problems in your group