Gases Behaviors of Gases

Gases… � Assume the SHAPE and VOLUME of

the container it occupies.

� Are easily compressed � Lots of free space between particles.

� Flow easily � Particles can move past one another.

(No attraction between particles)

3 Measurable Properties of Gases

� Volume � The amount of space a substance

takes up

� Temperature � Measure of average energy of motion

of gas particles

� Pressure � Force of the outward push

Gas Laws � 1. Boyle’s Law � Relationship between pressure and volume

� 2. Gay Lussac’s Law � Relationship between pressure and temperature

Boyle’s Law � Pressure increases à Volume

decreases � Pressure decreases à volume

increases � Variables are inversely

proportional (as one goes up the other goes down)

What does this graph show us?

Marshmallow Demo

Boyle’s Law Equation

P1 x V1 = P2 x V2

Where,

P = pressure (atm or equivalent)

V = volume (L or ml)

Example Problem �  V1= 2L

�  P1= 3 atm

�  P2= .5 atm

�  V2=?

Gay Lussac’s Law � Temp. increases à

pressure increases

� Temp. decreases à

pressure decreases

� Variables are directly proportional (both increase or decrease together)

Gay Lussac’s Law Equation

P1 P2 ___ = ___ T1 T2

Where,

P = pressure (atm)

T = temperature (K)

Gay Lussac’s Law Equation

P1 P2 ___ = ___ T1 T2

Where,

P = pressure (atm)

T = temperature (K)

Crush Soda Can Experiment 1.  Place one tablespoon of water into an empty soda

can..

2.  Heat the can on a hot plate to boil the water.

3.  What is happening to the air inside the can?

1.  Steam is created from the boiling water and expands inside of the can.

2.  The inside of the can was filled with air (gas) and water (liquid) and the liquid was heated until it changed states into a gas.

3.  The gas created (water vapor) pushed the original air outside of the can as the water vapor expanded to fill the space within the can.

Crush Soda Can Experiment 1.  Use tongs to lift the can off of the hot plate and turn it

upside down.

2.  Quickly, plunge the can mouth side down into a beaker of cold water.

3.  What happened to the gas inside the can? 1.  When the can was placed into the cold water, the gas

(water vapor), quickly condensed and turned back into water.

2.  The pressure that was being exerted on the walls of the can was removed when the gas turned back into a liquid.

3.  This experiment shows Gay Lussac’s Law in action. How? 1.  When the temperature was decreased, the pressure also

decreased. The decrease in pressure caused the can to implode.

So what does that mean? The pressure exerted on the sides of a soda can at about room temperature is 3.39 atm. That is equal to about 8 pounds of pressure on 1 square centimeter. That is a lot of pressure! Food for thought: It takes about 8 pounds of pressure to rip off a human ear.