1. Gas Notes

2. Physical Properties of all gases  Gases have mass  Gases are easily compressed –Air in you car tires, air in a basketball  Gases will expand to fill their container  Gases can easily travel through each other –wind  Gases exert pressure –The pressure is what makes a balloon blow up

3. The Kinetic-Molecular Theory 1.All gases have mass 2.Gas particles are widely spread apart 1.This is why you cannot see most gases 2.This is why gases can be easily compressed 3.Gas particles must be in constant, rapid motion 1.This is why gases completely fill their container.

4. Kinetic-Molecular Theory Continued 4.Gas particles exert pressure because they frequently collide with the walls of their container. 5.The average kinetic energy of the gas particles depends only on the temperature of the gas 1.Temp. is simply a measure of the kinetic energy of the particles 6.Gas particles are not attracted or repelled by one another.

5. 4 Variables for Gas 1.Amount of Gas Measured in moles Measured in moles Symbol used in equations  n Symbol used in equations  n How many moles of N 2 gas are in 4.72g of N 2 ?

6. 4 Variables for Gases 2.Volume –Gases fill their container completely and evenly –Volume of a gas is the same as the volume of the container it is in –Symbol used in equations  V –Units  Liters L

7. 3.Temperature –Usually measured in  C –Calculations usually use Kelvin (K) –K =  C + 273 Convert the following: a)25  C  K b)258 K   C c)100  C  K 4 Variables for Gases 25 + 273 = 298K  C 258 – 273 = -15  C 100 + 273 = 373K

8. 4 Variables for Gases 4.Pressure  A result of gas particles hitting the walls of the container it is enclosed in.  Symbol for pressure is P  Can be measured in –atm (atmospheric pressure) –Pa (Pascal) –mm Hg (millimeters of Mercury) –Lb/in 2 (pounds per square inch) –Torr –kPa (kilopascal)

9. Atmospheric Pressure  Atmospheric Pressure – pressure exerted by the weight of the air in the atmosphere  Units 1atm = 101,325 Pa = 760 mm Hg = 760 torr = 14.70 lb/in 2 = 101.325 kPa 1atm = 101,325 Pa = 760 mm Hg = 760 torr = 14.70 lb/in 2 = 101.325 kPa

10. Atmospheric Pressure  Pressure changes with altitude Pressure also changes with weather Water vapor (H 2 0) has a molar mass of 18g/mol and is lighter than normal air: 78% N 2 with a molar mass of 28g/mol and 21% O 2 with a molar mass of 32g/mol. Rain can be predicted: lowering atmospheric pressure = possible rain

11. Barometers  A barometer consists of a tube filled with mercury that is placed, upside-down, in an open dish of mercury.  The top of the tube is a vacuum.  The bottom of the tube is open to the atmosphere.

12. Measuring Atmospheric Pressure  Barometer – the mercury in the column will go down until the pressure from the atmosphere equals the pressure in the column of mercury  At sea level the column will measure 760 mm Hg

13. Manometers  A manometer is comprised of a bulb containing a gas and a U-shaped tube.  The U-shaped tube is partially filled with mercury.

14. Manometers  Depending on the pressure of the contained gas, the mercury shifts.  The difference between the heights of the mercury on each side of the tube is a measure of the difference in pressure of the gas compared to the atmospheric pressure.

15. Measuring Pressure of Enclosed Gases  Manometer –If the mercury levels are equal on both sides, the gas pressure is equal to the atmosphere –The gas pressure is greater than the atmospheric pressure

16. Calculating the gas pressure - difference between the 2 columns  Gas pressure is greater  you must add the two  760 + 44 = 804 mm Hg  Gas pressure is lower  you must subtract the two  760 – 22 = 738 mm Hg

17. Standard Temperature and Pressure  In problems you will see.... “STP” –This stands for “standard temperature and pressure”  Standard temperature = 273 K or 0  C  Standard pressure = 1atm or 760 mm Hg

18. Pressure Examples  Convert 456 mm Hg to Pa  Convert 324.3 kPa into atm

19. Manometer Examples  What is the pressure of an enclosed gas if the atmospheric pressure is 745 mm Hg and mercury column is 35 mm higher on the side open to the atmosphere?

20.  What is the atmospheric pressure (in units of atm) if the pressure of an enclosed gas is 0.987 atm and mercury is 33 mm higher on the side attached to the enclosed gas?