1. Homework: Pressure Worksheet (I need labs from some of you!!!)

2. Under pressure, the particles in a gas are forced closer together.
Compressibility
Gases are easily compressed because of the space between the particles in a gas.
The distance between particles in a gas is much greater than the distance between particles in a liquid or solid.
Under pressure, the particles in a gas are forced closer together.

3. Factors Affecting Gas Pressure
Aerosol Spray Paint
The pressure of the gas inside a new can of spray paint is greater than the air pressure outside the can. When gas rushes though an opening in the top of the can, it propels, or forces, paint out of the can. As the can is used, the pressure of the propellant decreases. Relating Cause and Effect What happens when the pressure of the propellant equals the air pressure outside the can?

4. Factors Affecting Gas Pressure
Three factors that affect gas pressure
amount of gas
volume
temperature

5. Factors Affecting Gas Pressure
Amount of Gas
As the amount of gas inside a container increases, the pressure inside of the container also increases

6. Factors Affecting Gas Pressure
If the gas pressure increases until it exceeds the strength of an enclosed, rigid container, the container will burst.
When a gas is pumped into a closed rigid container, the pressure increases as more particles are added. If the number of particles is doubled, the pressure will double. Predicting What would happen to the pressure in the container if the number of particles were tripled? If the number of particles were cut in half?

7. Factors Affecting Gas Pressure
Volume
By placing the same amount of gas in a smaller volume, you raise the pressure.
The more a gas is compressed, the greater is the pressure inside the container.
Volume down = pressure up

8. Factors Affecting Gas Pressure
When the volume of the container is halved, the pressure the gas exerts is doubled.
A piston can be used to force a gas in a cylinder into a smaller volume. When the volume is decreased, the pressure the gas exerts is increased. Interpreting Diagrams What happens to the gas pressure when the volume is reduced from 1 L to 0.5 L?

9. Factors Affecting Gas Pressure
Temperature
Heating a gas causes the pressure to increase.
Heating increases the kinetic energy, which makes the particles move with more energy
Temperature up = Pressure up

10. Factors Affecting Gas Pressure
When the Kelvin temperature of the enclosed gas doubles, the pressure of the enclosed gas doubles.
An increase in temperature causes an increase in the pressure of an enclosed gas. The container can explode if there is too great an increase in the pressure.

11. Manometer: a device used to determine vapor pressure of a liquid
13.2
Vapor Pressure
Manometer: a device used to determine vapor pressure of a liquid
The vapor pressure of a contained liquid can be measured in a manometer. The vapor pressure is equal to the difference in height of the mercury in the two arms of the U-tube. Calculating What is the difference in vapor pressure between ethanol at 0°C and ethanol at 20°C?

12. Pressure Conversions 1 atm = 760 mm Hg = 101325 Pa = 101
Pressure Conversions 1 atm = 760 mm Hg = Pa = kPa Use the ratio method.

13. How many mm Hg is 0.50 atm? 0.50 atm = 1 atm x mm Hg 760 mm HG

14. How many kPa is 0.50 atm?

15. How many atm is mm Hg?

16. How many kPa is 2.3 atm?

17. Ideal Gases and Real Gases
Under what conditions are real gases most likely to differ from ideal gases?

18. Ideal Gases and Real Gases
There are attractions between the particles in an ideal gas. Because of these attractions, a gas can condense,or even solidify, when it is compressed or cooled.
In this flask used to store liquid nitrogen, there are two walls with a vacuum in between.

19. Ideal Gases and Real Gases
Real gases differ most from an ideal gas at low temperatures and high pressures.

20. Ideal Gases and Real Gases
This graph shows how real gases deviate from the ideal gas law at high pressures. INTERPRETING GRAPHS a. Observing What are the values of (PV)/(nRT) for an ideal gas at 20,000 and 60,000 kPa? b. Comparing What variable is responsible for the differences between the two (CH4) curves? c. Making Generalizations How does an increase in pressure affect the (PV)/(nRT ) ratio for real gases?

21. 14.1 Section Quiz.
1. Compared to liquids and solids, gases are easily compressed because the particles in a gas
attract each other.
are spaced relatively far apart.
are very small.
repel each other.

22. 14.1 Section Quiz.
2. Gas pressure is affected by
temperature, volume, and the amount of the gas.
temperature, volume, and the molar mass of the gas.
phase diagram, volume, and the size of the container.
temperature, phase diagram, and the mass of the gas container.

23. 14.1 Section Quiz.
3. For gases, the SI units for volume (V), pressure (P), and temperature (T) are, respectively,
liters, kilopascals, and °C.
liters, kilopascals, and kelvins.
cm3, kilopascals, and kelvins.
liters, atmospheres, and °C.