GasGas

LawsLaws

ChemistryChemistrySemesterSemester IIII

NotesNotes

Characteristics of GasesCharacteristics of Gases

A.A. Properties of GasesProperties of Gases

Any amount of gas will expand and contract to occupy Any amount of gas will expand and contract to occupy the entire volume of its container. the entire volume of its container.

All gases with equal volumes will have equal numbers of All gases with equal volumes will have equal numbers of particlesparticles

Gases typically have low densities.Gases typically have low densities.

Gases are highly expandable and physically behave alike Gases are highly expandable and physically behave alike in response to pressure and temperature changes.in response to pressure and temperature changes.

Gases continuedGases continued

Temperature changes effect gases more Temperature changes effect gases more than liquids.than liquids.

Particles in gaseous phase are always Particles in gaseous phase are always moving in a constant random motion. They moving in a constant random motion. They are not in any fixed position.are not in any fixed position.

Size of the gas particles is extremely small Size of the gas particles is extremely small when compared to the space between them.when compared to the space between them.

B. Pressure and GasesB. Pressure and Gases

Gas pressure results from molecules colliding with Gas pressure results from molecules colliding with their container.their container.

Measure of pressure is in force/area.Measure of pressure is in force/area. Pressure in a closed system is equal in all Pressure in a closed system is equal in all

directions.directions.– Average air pressure at sea level is 101.325 kPa (kilopascals) Average air pressure at sea level is 101.325 kPa (kilopascals) – 1 pascal = 1 N/m1 pascal = 1 N/m2 2 (where N = Newton; a force)(where N = Newton; a force)– 1 kPa = 7.50 mm Hg1 kPa = 7.50 mm Hg

1 atm = 760 mm Hg = 101.325 kPa = 14.7 lb/in1 atm = 760 mm Hg = 101.325 kPa = 14.7 lb/in22

Pressure MeasurementPressure Measurement

Manometers are used to measure pressure in Manometers are used to measure pressure in open systems.open systems.

STP = Standard Temperature and PressureSTP = Standard Temperature and Pressure Gases are measured at STP, meaning Gases are measured at STP, meaning

101.325 kPa (also 760 mm of Hg or 1 atm) 101.325 kPa (also 760 mm of Hg or 1 atm)

and 273K (0and 273K (0o o C)C) Volumes are measured in Liters, mVolumes are measured in Liters, m3 3 or dmor dm33..