# TOPIC: Intro to Gases Do Now: Review Regents Q. What do you know about gases? He (g)

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TOPIC: Intro to Gases Do Now: Review Regents Q

What do you know about gases? He (g)

Properties of Gases 1.Gases have mass 2.Gases take shape & volume of container

Gases take the shape of their container

Properties of Gases 1.Gases have mass 2.Gases take shape & volume of container 3.Gases are compressible

Properties of Gases 1.Gases have mass 2.Gases take shape & volume of container 3.Gases are compressible 4.Gases easily move through each other (perfume, skunks!)  “Diffusion” 5.Gases exert pressure

Diffusion The movement of one material through another. Particles diffuse from high concentration to low concentration Rate of diffusion depends on size –Lighter particles diffuse more rapidly then heavier particles

Which gas will diffuse faster? Ammonia gas (NH 3 ) or Hydrogen Chloride (HCl) Ammonia gas (NH 3 ) N = 1 x 14 = 14 H = 3 x 1 = 3 Hydrogen Chloride (HCl) H= 1 x 1 = 1 Cl = 1 X 35 = 35 17 amu 36 amu

Properties of Gases 1.Gases have mass 2.Gases take shape & volume of container 3.Gases are compressible 4.Gases easily move through each other (perfume, skunks!)  “Diffusion” 5.Gases exert pressure

What is pressure? Pressure = force per unit areaPressure = force per unit area P = ForceP = Force Area Force = mass x acceleration

Why don’t the balloons keep expanding until they pop?

Atmospheric (air) Pressure

What is air pressure? pressure exerted on us by weight of gases above our heads (& all around our body)pressure exerted on us by weight of gases above our heads (& all around our body) At sea level (standard pressure) = 1 atmosphere (1 atm)At sea level (standard pressure) = 1 atmosphere (1 atm)

How does air pressure at top of Mt. Whitney (14,494 ft) compare to air pressure at John Jay? What about Death Valley (86 m below sea level)?

Torricelli Discovered air pressure & invented mercury barometer in 1643Discovered air pressure & invented mercury barometer in 1643 At 1 atm, the columns height is 760 mmHgAt 1 atm, the columns height is 760 mmHg So 1 atm – 7760 mmHg Or 1 atm = 760 Torr

Can we use H 2 O in a barometer? A water barometer has to be 13.6 times taller than a Hg barometer (D Hg = 13.6 g/ml) because … 13.6 times taller than a Hg barometer (D Hg = 13.6 g/ml) because … D water = 1.0 g/ml

Manometer Instrument used to measure atmospheric pressure Instrument used to measure pressure Wait, then what is a barometer?

Conversions 1 atm = 14.7 lb/in 2 U.S. pressure gauges1 atm = 14.7 lb/in 2 U.S. pressure gauges 1 atm = 101.3 kPa SI Units (Regents)1 atm = 101.3 kPa SI Units (Regents) (kPa = kilopascal) 1 atm = 760 Torr or 760 mm Hg CHEMISTRY1 atm = 760 Torr or 760 mm Hg CHEMISTRY

Given Conversion Factor

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