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 m3 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 101.3 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 pump The 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

• PT = P1+P2+P3…

Boyle’s Law

• Inversely relates pressure and volume

• P1V1=P2V2

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.

P1V1 = P2V2

Charles’s Law

• Directly relates volume and temperature

• V1/T1 = V2/T2

Gay-Lussac’s Law

• Directly relates pressure and temperature

• P1/T1=P2/T2

Combined Gas Law

• Equation?

Do Now

1. The density of air is about 1.29 g/cm3. If a balloon is filled with a gas that has a density of 1.28 g/cm3, 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/m3. 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 forceequal to the weight of the air displaced.

Archimedes

Air Buoyancy

An object surrounded by air is buoyed up by a forceequal to the weight of the air displaced.

Archimedes

Air Buoyancy1937

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