Gas Properties: Pressure, Volume, Temperature, and Amount (Chapter 6)

1. Chapter 6 Gases

2. Properties of Gases • Kinetic theory helps explain some of the characteristics of a gas. • - The molecules do not attract or repel one another and move randomly colliding with each other. • -   temperature  molecules move faster. • Gases are described in terms of a number of properties: 1.     Pressure (P) 2.     Volume (V) 3.     Temperature (T) 4.     Amount of Gas (n)

7. Changes in air pressure • At sea level (eg. Los Angeles) there are more air particles  atmospheric pressure = 1atm or 760 mmHg. • At the top of Whiteface mountain pressure is considerably less than 760 mmHg. In fact it is closer to 630 mmHg. (at the top of Everest = 270 mmHg). • Water is denser than air. Thus divers experience increased pressure under water……….at 100ft he/she will experience 4 atm and must adjust the breathing mixture to match the increase in pressure.

9. Blood pressure is measured as “mmHg”. Blood pressure is required to push the blood around the body. • Normal b.p = 120/80 mmHg. • ­             systolic diastolic (contraction) (relaxation)

10. Vapor Pressure • Remember liquid molecules can break away from the surface to become gas particles or vapor. In a closed container the molecules cannot evaporate………this creates a pressure called vapor pressure. • Boiling point = point when vapor pressure is equal to external pressure. • At higher altitudes the atmospheric pressure is lower so the boiling point is less. Eg.  • Vapor pressure at sea level = 760 mmHg…….boiling point = 100 oC • Vapor pressure at Whiteface = 630mmHg……..boiling point = 95 oC

11. Boyles Law • Describes the relationship between the pressure and volume of a gas. Law states: • If temperature and amount of gas are kept constant, then Volume of gas changes inversely with the pressure. P1V1 = P2V2 • For this to hold true the temp. and amount of gas must be unchanged.

15. Problem Time! • If there is no temperature change or change in the number of moles calculate the new pressure of helium gas if the initial volume and pressure were 250ml and 800 torr respectively and the final volume was 500 ml? P1V1 = P2V2 800 torr x 250mL = P2 x 500 mL 200 000/500 = P2 400 torr=P2

19. Charles’ Law • If pressure and the amount of gas remain unchanged, Then volume of gas is directly related to the temperature. V1 = V2 T1 T2 • Remember all temperatures must be converted to Kelvin (K) temperature! • Temp (K) = temp (oC) + 273 

25. Problem Time! • A 25.0 ml bubble is released from a diver’s air tank at a pressure of 4.00 atm and a temperature of 11oC. What is the volume of the bubble when it reaches the ocean surface where the pressure is 1.00 atm and the temperature is 18oC? P1V1 = P2V2 T1 T2 4.00 x 25 = 1.00 x V2 284 291 102.5 mL = V2

29. Avogadros Law • Until now the amount of gas (n) has always been constant. What if there is a change in the of moles of the gas?

39. Dalton’s Law • Many gas samples are a mixture of gases………..each gas in the mixture exerts a partial pressure. • The total gas pressure is the sum of the partial pressures of all the gases in the mixture…………….this is Dalton’s Law. P total = P1 + P2 + P3 + …………………..

48. Henry’s Law • “The amount of gas that will dissolve in a liquid at a particular temperature is directly related to the pressure of that gas above the liquid”. • Consider a can of soda………………………….carbon dioxide in the can “air space” is high to permit sufficient CO2 to be dissolved in the liquid to make it “fizzy”.