10 2 NOTES Gas Pressure C Gas Pressure

  • Slides: 10
Download presentation
10. 2 NOTES Gas Pressure

10. 2 NOTES Gas Pressure

 • C. Gas Pressure • 1. Pressure force per unit area • -

• C. Gas Pressure • 1. Pressure force per unit area • - air pressure at higher altitudes is slightly lower than at sea level (due to decreased mass in upper atmosphere) • - examples of force per area - snow and snow shoes; ax vs. hammer •

 • 2. Measuring air pressure - Torricelli was first to demonstrate air exerted

• 2. Measuring air pressure - Torricelli was first to demonstrate air exerted pressure • Barometer instrument used to measure atmospheric pressure • - height of mercury is a barometer is always about 760 mm • - actual height based on two factors: gravity and atmospheric pressure • - increase air pressure, causes Hg to rise, decrease AP, Hg will fall;

 • 3. Units of pressure SI unit of pressure is the Pascal (Pa)

• 3. Units of pressure SI unit of pressure is the Pascal (Pa) • - Pa = 1 N/m 2 (Newton = kg. Xm/s 2) • - At sea level (temp. of 0°C) – avg air pressure = 760 mm. Hg • – known as 1 atm; 1 atm = 101. 3 k. Pa = 760 mm. Hg (∞ sig figs); 760 torr (∞ sig figs); 14. 7 psi

 • 4. Dalton’s Law of Partial Pressures - each gas in a mixture

• 4. Dalton’s Law of Partial Pressures - each gas in a mixture exerts pressure independently of the other gases present; • Ptotal = PA + PB + PC

 • Partial pressure of any gas depends on the # of moles of

• Partial pressure of any gas depends on the # of moles of the gas, size of the container and temperature of the mixture • it does not depend on the identity of the gas! • At a given T and P, the partial pressure of one mole of any gas is the same • if the percentage of a mixture is known as well as the total pressure, it is possible to determine the partial pressure of each gas • multiply the % times the total pressure = partial pressure of gas b/c partial pressures of gases at the same temp. are related to their concentration;

 • Collecting over water certain gases must be collected over water (oxygen) •

• Collecting over water certain gases must be collected over water (oxygen) • when this happens, water vapor will also be collected; • • • vapor pressure – pressure exerted by a vapor in equilibrium with its liquid • liquid w/ strong attractive forces (glycerol) have a low VP; while those with weak attractive forces (ether) have high VP; water vapor exerts a pressure and must be accounted for; • water vapor pressure dependent on temperature of the system, can look it up;

 • Sample Problem – A sample of oxygen is collected over water at

• Sample Problem – A sample of oxygen is collected over water at a temperature of 22°C. The pressure of the system was 764. 2 mm. Hg. What is the pressure of the DRY oxygen? • Ptotal = P 1 + P 2 + P 3 + … • 764. 2 = PO 2 + 19. 8 PO 2 = 744. 4 mm. Hg