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GASES. Identify the abundances of the naturally occurring gases in the atmosphere. Describe the historical development of the measurement of pressure.

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Presentation on theme: "GASES. Identify the abundances of the naturally occurring gases in the atmosphere. Describe the historical development of the measurement of pressure."— Presentation transcript:

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.


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