The Gas Laws

Gases have properties which we can observe

with our senses

These properties include: pressure (p), temperature, mass, and the volume (V) which contains the gas.

Gas in a Balloon• Gas molecules inside a

volume (a balloon) are constantly moving around freely.

• During this molecular motion they frequently collide with each other and with the surface of any enclosure there may be (in a small balloon there are many billions of collisions each second).

Factors that Affect Gas Pressure

• What changes might affect the pressure of a gas in a container?

• Temperature• Volume• Number of particles

Section 2 Behavior of Gases

Describing Gas Behavior

• Temperature Temperature is a measure of how fast the particles in an object are moving.The faster the particles are moving, the more energy they have.

• Volume Volume is the amount of space that an object takes up. Because gas particles spread out, the volume of any gas depends on the container that the gas is in.

Chapter 3

Section 2 Behavior of Gases

Describing Gas Behavior, continued

• Pressure The amount of force exerted on a given area of surface is called pressure. 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

• Reducing the volume of a gas increases its pressure if the temperature of the gas and the number of particles are constant

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 is the action of a 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.

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

• Deep sea fish die when brought to the surface.

• Pushing in the plunger of a plugged-up syringe decreases the volume of air trapped under the plunger.

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.

Temperature Pressure Relationship

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

• • 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

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.smm.org/heart/lungs/breathing.htm