1. What is Gas Pressure? What are the factors influencing Pressure? Gas Pressure Volume Temperature How do we measure each?

2. K-W-L :What is gas pressure? From the KMT, we know that gas particles are always in motion colliding with each other and other objects. These collisions exert a small individual force but collectively exert a large force, termed gas pressure. THINK! What is happening to the particles inside this balloon? Gas particles are bouncing around, hitting each other, hitting the edges of the balloon, and causing the balloon to inflate.

3. QUESTION 1 : If air is made up of a mixture of gases, does air exert a pressure on Earth? YES! Air molecules exert a pressure because the force of gravity is holding air particles in the Earth’s atmosphere. Atmospheric Pressure - results from collisions of atoms and molecules in air with objects

4. QUESTION 2 : Does atmospheric pressure change as we increase altitude? Or does it always stay the same? Atm pressure decreases as you increase in altitude because the density of the air also decreases. Not as many particles colliding way up there!

5. What about a vacuum of space? How does that work? Vacuum- a volume of space that is empty of matter, including air, so that gas pressure is much less than atmospheric pressure No Air » No Particles » No Collisions » No Pressure

6. How do we measure atmospheric pressure? Barometer- device used to measure atm pressure, created in 1643 by Italian scientist Evangelista Torricelli How it works: Mercury filled tube is inverted into a dish causing some of the mercury to exit the tube into the dish. The amount of mercury exiting the tube or left in the tube is dependent upon the air pressure outside the tube. Therefore, air pressure can be measured using a barometer. At std atm = 760 mm Hg BUT WAIT, THERE’S MORE!

7. What about a manometer? Manometer- used to measure the pressure of gas in a container How it works: the measured gas pressure is applied to one side of the tube while the reference pressure (atm pressure) is applied to the other Left = Gas Pressure less than Atm pressure Right = Gas Pressure greater than Atm pressure

8. What units do we use to measure pressure? LOTS! 1 standard atmosphere = 760 mm Hg 760 torr 101.325 kPa 101,325 Pa 29.92 inches 14.7 pounds/in 2 (psi) Also helpful when measuring….. 1 torr = 1 mm Hg

9. Let’s Practice converting between units! 1. What is 475 mm Hg expressed in atm? 475 mm Hg x 1 atm = 0.625 atm 760 mm Hg 2. The pressure of a tire is measured as 29.4 psi. What is the pressure in mm Hg? 29.4 psi x 760 mm Hg = 1.52 x 10 3 mm Hg 14.7 psi 3. What is 2 atm expressed in torr? 2 atm x 760 torr = 1520 torr 1 atm

10. Now, we know about gas pressure and how to measure it, what other factors influence pressure? TemperatureVolume Let’s start with Temperature!

11. Temperature Temperature- the measure of the average kinetic energy of the particles in a sample of matter... NOT HEAT! As Temp Measured using various scales including: 1. Celsius (°C) -- freezing point of water (O°C), boiling point of water (100 °C) 2. Fahrenheit (°F) -- freezing point of water (32 °F), boiling point of water (212 °F) 3. Kelvin (K) -- WHAT IS THIS!, energy & collisions

12. Comparisons of Temperature Scales

13. KELVIN (K): Known as absolute temperature scale-- as the zero point of the scale is considered the lowest possible temperature of anything in the universe! At freezing point of water = 273 K, the boiling point of water = 373 K K = °C+ 273 **NOTICE- no degree sign** °C = 5/9 (°F -32) °F = (9/5 °C) +32 Lord Kelvin

14. What is volume? How do we measure different types of matter? Volume = amount of space occupied by matter, As Volume mL cm 3 gallon, quarts, liter SI Unit of measurement for volume = m 3 Gases typically measured in terms of liters or m 3 !, particle collisions

15. SUMMARY Gas Pressure results from gas particle collisions with objects and other particles exerting a force upon contact. Atmospheric Pressure results from air particles colliding with each other and objects and is ALWAYS affecting us even though we don’t always notice it! Use manometer and barometer to measure gas and atm pressure, respectively in atm, torr, mm Hg, kPa, Pa, inches, bar. Temperature measured in Kelvin effects gas particle collisions. Volume measured in liters, m 3, mL (depending on the substance) also affects gas particle collisions.

16. Crush the Can Demo Let’s examine the effect of atmospheric pressure. BEFORE we get started: 1. What is inside the empty pop can ? 2. What is happening to the water in the can when it is heated? 3. What will happen to the can when I put it upside down in the cold water? AFTER we crush the can: 4. Why did the can collapse (using KMT)? 5. How could I make the can expand?

17. DON’T Answer the questions on your handout sheet to turn in at the end of class! Check out your concept map to visualize how it all relates!