GASES

The weight of air causes atmospheric pressure. Atmospheric pressure is actually greater at shoulder level than at head level!

Does the Atmosphere Have Weight? Sea Level 1 m 3 has a mass of approximately 1.2 kg. 1 kg weighs 9.8 N. Weight of the atmosphere on one square meter is approximately 100,000 N or 100 kPa! More exactly, the average atmospheric pressure at sea level is kilopascals (101.3 kPa). The Atmosphere is about 50 miles “deep” exerting 14.7 psi at sea level.

How Do We Measure the Weight? Simple Mercury Barometer

How Do We Measure the Pressure? The greater the atmospheric pressure, the higher the liquid rises in the tube 760mm

Aneroid Barometer

How Do We Measure the Pressure? The stylish weatherglass

Just like drinking from a straw! Area of low pressure Area of high pressure The liquid is pushed up by atmospheric pressure.

Gases travel from high to low pressure areas. The classic water pumpThe vacuum pump

Pressure & Force P = defined as the force per unit area on a surface = force/area Force unit = Newton (N)

Misc. Info Pressure depends on area of contact; smaller area, greater pressure Ex.: high heels; ballerina Atmosphere exerts pressure - total of individual gas pressures (mostly N, then O) Measured using barometers Units: 1 torr = 1 mm Hg

Dalton’s Law of Partial Pressures Partial pressures are exerted by individual gases Law states that total pressure of a gas mixture is the sum of the component pressures P T = P 1 +P 2 +P 3 …

Boyle’s Law Inversely relates pressure and volume P 1 V 1 =P 2 V 2

Boyle’s Law When the density of a gas increases, the pressure increases.

Boyle’s Law When the volume of a gas decreases, the pressure increases. P 1 V 1 = P 2 V 2

Charles’s Law Directly relates volume and temperature V 1 /T 1 = V 2 /T 2

Gay-Lussac’s Law Directly relates pressure and temperature P 1 /T 1 =P 2 /T 2

Combined Gas Law Equation?

Do Now 1.The density of air is about 1.29 g/cm 3. If a balloon is filled with a gas that has a density of 1.28 g/cm 3, what will happen to it? 2.If the volume of a sample of gas is reduced by half (crushed down to half it’s size) what will happen to the pressure? 3.When air is compressed, what happens to its density? 4.The atmosphere of pluto is 3 times as dense as the atmosphere of earth (760 mm Hg). What would be, then, the pressure in mm Hg? 5.If the volume of a 4L sample of gas at a pressure of 5 atm is suddenly reduced to 1 L, what will the final pressure be? 6.At sea level, 1 cubic meter of air at 20 degrees Celsius has a mass of about 1.2 kg/m 3. About how many kilograms of air occupy a classroom that has a 200-square-meter floor area and a 4-meter-high ceiling?

Air Buoyancy An object surrounded by air is buoyed up by a force equal to the weight of the air displaced. Archimedes

Air Buoyancy An object surrounded by air is buoyed up by a force equal to the weight of the air displaced. Archimedes

Air Buoyancy 1937 Lakehurst. New Jersey. In 32 seconds the 804-foot long dirigible Hidenburg was destroyed as the 7 million cubic feet of hydrogen caught fire. 35 perish in this spectacular explosion.

When the speed of a fluid increases, pressure in the fluid decreases. Fluid flows more quickly through narrow sections and the pressure decreases. Conservation of energy: kinetic energy and pressure Bernoulli’s Principle Lift