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10.1 Characteristics of gases

10.1 Characteristics of gases. Gas is one of the three states of matter. It is characterized by it's low density. The other states of matter are liquid and solid. Only a few elements exist as gases under ordinary conditions: - The noble gases: He, Ne, Ar , Kr and Xe ( monoatomic )

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10.1 Characteristics of gases

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  1. 10.1 Characteristics of gases • Gas is one of the three states of matter. It is characterized by it's low density. The other states of matter are liquid and solid. • Only a few elements exist as gases under ordinary conditions: • - The noble gases: He, Ne, Ar, Kr and Xe (monoatomic) • - H2, N2, O2, F2 and Cl2 (diatomic gases) • Gas differ significantly from solids and liquids: • A gas expands spontaneously to fill its container • The volume of a gas equals the volume of the container in which it is held • Gases also are highly compressible

  2. 10.2 Pressure Pressure is a force exerted by the substance per unit area on another substance. Force F P = Pressure = A Area Gases exert a pressure on any surface with which they are in contact

  3. Atmospheric pressure and the barometer Atmospheric pressure is the pressure exerted by earth’s atmosphere Value of atmospheric pressure depends on location, temperature and weather condition 76 cm Standard atmospheric pressure (1 atm) is equal to the pressure that supports a column of mercury exactly 760 mm (or 76 cm) height at 0C at sea level. 1 atm = 760 mmHg = 760 torr A barometer measures atmospheric pressure by balance the weight of mercury in a glass tube against the weight of air in the atmosphere. = 76 cmHg = 101325 Pa = 101.325 kPa

  4. Example: The atmospheric pressure at a certain location is 732 mmHg. Convert the pressure in atm and Pa? 1 atm Pressure (in atm)= 732 mmHg  760 mmHg = 0.963 atm 101325 Pa Pressure (in Pa)= 732 mmHg  = 97591.9 Pa 760 mmHg = 97.5919 kPa

  5. A manometer is used to measure the pressure of an enclosed gas. Their operation is similar to the barometer, and they usually contain mercury A mercury manometer, used to measure gas pressures near atmospheric pressure.

  6. Example: The level of mercury in an open-end arm of the manometer has a height of 136.4 mm, and the mercury in the arm that is in contact with the gas has a height of 103.8 mm. What is the pressure of the gas (a) in atmospheres, (b) in kPa [atmospheric pressure is 764.7 torr] (a) Pressure of gas, Pgas = Patm + h = 764.7 torr + (136.4 torr – 103.8 torr) = 797.3 torr Pgas = = 1.049 atm 101.325 kPa 1 atm =(1.049 atm) (797.3 torr)  1 atm 760 torr (b) P in kPa = 106.3 kPa

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