The Gas Laws

Properties of Gases

• Occupy space• Have mass• No definite shape or volume• Unconfined gases expand

indefinitely• Have low density

Gas in a Balloon• Gas molecules inside

the balloon are constantly moving around freely.

• They collide with each other and with the surface of the balloon

• in a small balloon there are many billions of collisions each second!

What factors affect Gas Pressure?

• Temperature• Volume• Number of particles

•Temperature: a measure of how fast the particles in an object are moving.

•The faster the particles move, the more energy they must have.

Chapter 3

Temperature

Volume

• Volume: the amount of space that an object takes up.

• The volume of any gas depends on the container that the gas is in.

of Gases

Pressure

• Pressure: amount of force exerted on a given area of surface

•You can think of pressure as the number of times the particles of a gas hit the inside of their container.

Chapter 3

Robert Boyle investigated the relationship between the volume of a gas and its pressure

Volume and Pressure Relationship

• Volume and pressure are inversely related

• If I reduce the volume of the container, I increase the pressure of the gas

Volume vs Pressure• When he

changed the pressure the volume responded in the opposite direction.

Boyle’s Law

• Boyle’s Law states that the volume of a gas is inversely proportional to its pressure if the temperature and the number of particles are constant.

A practical application of Boyle’s Law: syringe

• When fluids are drawn into a syringe, the volume inside the syringe is increased.

• the pressure decreases on the inside

• the pressure on the outside of the syringe is greater

• Fluids are forced into the syringe.

• pushing the plunger in decreases the volume on the inside

• increases the pressure inside and makes it greater than outside

• fluids are forced out. • http://revver.com/video/821971/

imaginationland-creatures-in-a-vacuum-easter-demo/

• bubbles exhaled by a scuba diver grow as the approach the surface of the ocean.

• Deep sea fish explode when brought to the surface rapidly.

Other example of Boyle’s Law

Charles’ Law

• Doubling the temperature of a gas doubles its volume, as long as the pressure of the gas and the amount of gas isn't changed.

• http://education.jlab.org/frost/balloon.html

Temperature Pressure Relationship

• There is a direct relationship between the pressure of the gas and the temperature of the gas

• The pressure of a gas increases as the temperature increases.

• As the temperature decreases, the pressure decreases.

• The particles in a gas are moving. They bump into the walls creating a pressure. • When a gas is heated, its particles speed up.

Why does gas pressure increase when the temperature increases?

There are two ways that this increases the pressure:

•the faster particles bump into the container walls more often

•each collision is harder because the particles are moving faster.

• A football inflated inside and then taken outdoors on a winter day shrinks slightly.

• A slightly underinflated rubber life raft left in bright sunlight swells up

• The plunger on a turkey syringe thermometer pops out when the turkey is done

Examples of Charles’ Law

Gas Behavior Laws

• Boyle’s Law Boyle’s law states that for a fixed amount of gas at a constant temperature, the volume of the gas is inversely related to pressure.

P1V1 = P2V2

• Charles’s Law Charles’s law states that for a fixed amount of gas at a constant pressure, the volume of the gas changes in the same way that the temperature of the gas changes.

T1V2 = T2V1

Section 2 Behavior of GasesChapter 3

• http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/boyles_law_graph.html

• http://www.jersey.uoregon.edu/vlab/Piston

• http://www.grc.nasa.gov/WW/K-12/airplane/Animation/frglab2.html

The Combined Gas Law• Combination of Boyle’s and

Charles’ laws• The volume of gas is directly

proportional to the temperature and inversely proportional to the pressure. • P1V1 P2V2

T1 = T2

  How You Breathe• Your lungs are are

made of spongy, elastic tissue that stretches and constricts as you breathe.

• The airways that bring air into the lungs are made of smooth muscle and cartilage, allowing the airways to constrict and expand.

• What we need is a way to create air pressure to draw the air into our bodies.

• Atmospheric pressure is about 760 mm Hg. 

• Since the flow is always from an higher to lower, we have to be able to make our respiratory tract have a lower pressure than 760 mm Hg.

• How can we decrease the pressure within our respiratory tract?

This is the trick.

•   In order to decrease the pressure within our respiratory tract, we have to expand our container, our chest. If we can expand our chest, the air pressure within will fall, and air will rush into our respiratory tract.

Inhaling

• When you inhale, the diaphragm and the muscles between your ribs contract and expand the chest cavity.

• This expansion lowers the pressure in the chest cavity below the outside air pressure. Air then flows in through the airways (from high pressure to low pressure) and inflates the lungs.

Inhalation and exhalation

• When you exhale, the diaphragm and rib muscles relax and the chest cavity gets smaller.

• The decrease in volume of the cavity increases the pressure in the chest cavity above the outside air pressure.

• Air from the lungs (high pressure) then flows out of the airways to the outside air (low pressure). The cycle then repeats with each breath.

• http://www.youtube.com/watch?v=n5bsQ_YDYCI