1. GASES

2. Identify the abundances of the naturally occurring gases in the atmosphere. Describe the historical development of the measurement of pressure. Describe the various units used to measure pressure.

3. Earth’s air is composed of two types of gases: PermanentVariable Nitrogen 78.1%Water vapor 0 - 4% Oxygen 20.9%Carbon Dioxide 0.035% Argon 0.9%Methane 0.0002% Neon 0.002%Ozone 0.000004% Helium 0.0005% Krypton 0.0001% Hydrogen 0.00005%

4. Torricelli (1608-1647) developed the first barometer - measures air pressure Height of mercury supported by atmospheric pressure at sea level is 760 mm.

5. Pascal (1623-1662) added to Torricelli’s “barometer.” Discovered height affects the pressure of the atmosphere. SI unit of pressure – ‘Pascal’ - kPa Gay-Lussac (1778-1850) observed the law of combining volumes in chemical reactions. Two volumes of hydrogen combined with one volume of oxygen to form two volumes of water.

6. Avogadro (1776-1856) Avogadro’s Hypothesis - any sample of any gas at the same temperature and pressure will contain the same number of particles.

7. UNITS

8. 1. atmosphere (atm): 1 atm is equal to 760 mmHg, or 101.325 kPa 2. Pascal (Pa) – standard international (SI) units. Defined as 1 Newton of force per m 2. Use kiloPascals. 3. Millimetres of mercury (mmHg) – not commonly used. 4. Pounds per square inch (psi) - Imperial unit (uncommon) 1 kPa is equal to 0.145 psi 1 atm is equal to 14.7 psi.

9. Manometer – measure gas pressure:

10. Vapour Pressure: P gas = P atm + h (greater than air) P gas = P atm – h (less than air) P gas = P atm + h P gas = 762 mm + 15 mm = 777 mm Hg Convert to SI units: If 760 mmHg = 101.3 kPa, then

11. Gas pressure is due to the force of gaseous particles colliding with their container. Torricelli invented the barometer to measure atmospheric pressure. Units used: mmHg, atm, kPa, psi Using a manometer: gas pressure > air pressure P gas = P atm + h gas pressure < air pressure P gas = P atm – h.