8th grade-ch. 2 sec. 3 behavior of gases

Ch. 2 Sec. 3Behavior of

Gases

3 propertiesof gas that

can be measured

volume temperature pressure

measure of average energy of

motion of particles of substance

force of its outwardpush divided by

area of wallsof its container

pressure = force

area

1. Boyle’s law• pressure increases volume decreases• pressure decreases volume increases

• variables – inversely proportional

Boyle's Law Interactive animation

As a balloon rises in the atmosphere, the air pressure decreases.

As the air pressure decreases, the helium inside the balloon expands, stretching the balloon to a greater volume.

IT’S A GAS ACTIVITY PG. 66DATA TABLE

Adding books Removing books

# of books Volume (cm3, cc,

mL)

# of books Volume (cm3, cc,

mL)

0 5

1 4

2 3

3 2

4 1

5 0

temp. increases pressure increases

temp. decreases pressure decreases

- applies to gas that cannot change volume (gas kept in closed, rigid container)- variables – directly proportional to each other

2. Ideal Gas Law

Crush soda can experiment• Before adding water to the soda can, the can is filled with

air. When water is added some of the air is displaced. • Heating the water causes it to boil and the resulting steam

expands inside the can, pushing most of the remaining air out of the can. When the can is cooled in the room temperature water, the steam changes to liquid water, which takes up much less space than steam.

• This change takes place while the opening of the can is under water, so no air is able to rush into the can to take up the extra space. The pressure inside the can is therefore much less than the pressure on the outside of the can, and so the can implodes.

2. Ideal Gas Lawtemp. increases pressure increasestemp. decreases pressure decreases

As the temperature increases so does the pressure.

• Pressure is not only a matter of altitude but also is dependent upon the temperature. As the temperature increases so does the pressure.

• The molecules and atoms that comprise the air we breath gain energy as they absorb heat. That increase in energy results in faster moving atoms which we observe as an increase in energy.

• The opposite occurs when the temperature decreases. As the molecules lose energy, their motion is decreased and we observe a decrease in pressure.

Procedure1. Place two cups of hot tap water into each two 2-liter bottle.

2. Place your thumb over each bottle opening and shake. This ensures the air inside the bottle is warmed.

3. Pour the water out of each bottle and screw a bottle cap on only one of the two bottles.

4. Stand both bottles side-by-side and observe over the next 5 minutes.

3. Charles’ Law• temp. increases volume increases• temp. decreases volume decreases

• variables - directly proportional to each other

Interactive Charles Law animation

Charles’ Law demo. blow dryer, 2L bottle, & balloon

1. Put balloon on 2L bottle

2. Point blow dryer at bottle

3. What happens?

4. Balloon inflates

5. Put bottle with balloon in cold tub of water

6. What happens?

7. Balloon deflates

Which law does this picture represent? Explain.

1. Boyle’s law

pressure increases volume decreases

pressure decreases volume increases

Crush soda can experiment• Before adding water to the soda can, the can is filled with

air. When water is added some of the air is displaced. • Heating the water causes it to boil and the resulting steam

expands inside the can, pushing most of the remaining air out of the can. When the can is cooled in the room temperature water, the steam changes to liquid water, which takes up much less space than steam.

• This change takes place while the opening of the can is under water, so no air is able to rush into the can to take up the extra space. The pressure inside the can is therefore much less than the pressure on the outside of the can, and so the can implodes.

2. Ideal Gas Lawtemp. increases pressure increasestemp. decreases pressure decreases

Can crush demonstration

Can Crush explanation

What happens when a balloon is cooled with liquid nitrogen?

For an "ideal gas" pressure x volume is proportional to the absolute temperature. (PV = nRT)

When the temperature, T, goes down PV decreases and the balloon collapses.

Which law does this picture represent? Explain.

3. Charles’s Law

temp. increases volume increases

temp. decreases volume decreases

Write a fairy tale, including examples of the 3 gas laws. Underline the gas

laws in your story.

Interactive Gas Laws animationGAS LAWS CENTER ACTIVITIES