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GASES. Chapter Thirteen: The Behavior of Gases. 13.1 Gases, Pressure, and the Atmosphere 13.2 The Gas Laws. Chapter 13.1 Learning Goals. Describe the composition of Earth’s atmosphere. Make comparisons between Earth’s atmosphere and the atmospheres of other planets. - PowerPoint PPT Presentation
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GASES
Chapter Thirteen: The Behavior of Gases
13.1 Gases, Pressure, and the Atmosphere
13.2 The Gas Laws
Chapter 13.1 Learning Goals
Describe the composition of Earth’s atmosphere.
Make comparisons between Earth’s atmosphere and the atmospheres of other planets.
Explain the meaning of atmospheric pressure and describe how it is measured.
Investigation 13A
Key Question:How are temperature
and pressure of a gas related?
Pressure Temperature Relationship
13.1 What’s in Earth’s atmosphere?
Nitrogen (N2) gas makes up about 78 percent of Earth’s atmosphere.
Nitrogen is released into the air by volcanoes and decaying organisms and is a vital element for living things.
13.1 Comparing atmospheresAn atmosphere is a layer of gases
surrounding a planet or other body in space.
13.1 Life changed Earth’s atmosphere
Over time, photosynthesis breaks down carbon dioxide, uses carbon to build the organism, and releases oxygen into the air.
13.1 Life changed Earth’s atmosphere
Earth stores carbon as calcium carbonate so it doesn’t return to the atmosphere.
“Fossil fuels” (oil, coal, and natural gas) are carbon from decaying plants and animals in the ground.
13.1 Atmospheric pressure
Atmospheric pressure is a measurement of the force of air molecules in the atmosphere at a given altitude.
Your ear drum is one way you can detect changes in pressure.
13.1 Pressure in the atmosphereAt sea level, the
weight of the column of air above a person is about 9,800 newtons (2,200 pounds)!
This is equal to the weight of a small car.
Why aren’t we crushed by this pressure?
13.1 Measuring Pressure
A barometer is an instrument that measures atmospheric pressure.
Mercury barometers were common until we discovered their vapors were harmful.
13.1 Measuring PressureToday we use
aneroid barometers.
They have an airtight cylinder made of thin metal.
The walls of the cylinder respond to changes in pressure.
13.1 Pressure in the
atmosphereThe gas molecules closest to Earth’s surface are packed together very closely.
This means pressure is lower the higher up you go into the atmosphere.
13.1 Pressure changes with altitude
13.1 Units of pressure
Chapter Thirteen: The Behavior of Gases
13.1 Gases, Pressure, and the Atmosphere
13.2 The Gas Laws
Chapter 13.2 Learning Goals
Explain how pressure, temperature, volume, and the number of molecules in a gas are related when one or more of these factors in held constant.
Apply the gas laws to solve problems.
Analyze graphs of data to explain how factors like pressure and volume are related.
Investigation 13B
Key Question:How are pressure and volume of a gas
related?
Boyle’s Law
13.2 Boyle’s Law When you
squeeze a fixed quantity of gas into a smaller volume the pressure goes up.
This rule is known as Boyle’s law.
Solving Problems
A kit used to fix flat tires consists of an aerosol can containing compressed air and a patch to seal the hole in the tire.
Suppose 5 liters of air at atmospheric pressure (1 atm) is compressed into a 0.5 liter aerosol can. What is the pressure of the compressed air in the can?
Assume no change in temperature or mass.
1. Looking for: …final pressure in atmospheres (P2)
2. Given …V1 = 5 L , P1= 1 atm, V2 = .5 L
3. Relationships: Boyle’s Law: P1V1 = P2V2
4. Solution Rearrange equation so P2 = P1V1 / V2
P2 = 1atm x 5.0 L/ 0.5 L = 10 atm.
Solving Problems
13.2 Pressure and TemperatureThe pressure of a gas is
affected by temperature changes.
If the mass and volume are kept constant, the pressure goes up when the temperature goes up, and down when the temperature goes down.
13.2 Gay-Lussac’s Law
13.2 Pressure and TemperatureAny time we apply gas laws, the the
temperature must be in Kelvins.
Only the Kelvin scale starts from absolute zero, when energy of particles is theoretically zero.
13.2 Charles’ LawAccording to Charles’ law, the volume of
a gas increases with increasing temperature.
Volume decreases with decreasing temperature.
13.2 Charles’ Law
A hot-air balloon floats because the air inside is less dense than the air outside.
Solving Problems
A can of hair spray has a pressure of 300 psi at room temperature 21°C.
The can is accidentally moved too close to a fire and its temperature increases to 295°C.
What is the final pressure in the can? (Round answer to nearest whole number.)
1. Looking for: …final pressure in atmospheres (P2)
2. Given …P1= 300 atm, T1 = 21 C , T2 = 295 C
3. Relationships: Convert temps using K = C + 273 Charles’ Law: P1/T1 = P2/T2
4. Solution Rearrange equation so P2 = P1xT2 / T1
P2 = 300 atm. x 568K / 294K = 580 atm.
Solving Problems
Investigation 13C
Key Question:What is the relationship between the volume
and temperature of a gas?
Charles’ Law
Up, Up and AwayAirplanes use air pressure in
many different ways. Air pressure is used to keep an aircraft in the air as well as to propel it forward. Flight instruments use air pressure to measure altitude, air speed, and vertical speed. Finally, a pressurized airplane uses air pressure to maintain appropriate pressure for human survival in its cabin.