1. Boyle’s Law Charles’ Law Gay-Lussac’s Law
The Gas Laws
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law

2. Behavior of Gases
16.3
Pressure
Pressure is the amount of force exerted per unit of area, or P = F/A.
A balloon and a bicycle tire are considered to be containers.
They remain inflated because of collisions the air particles have with the walls of their container.

3. Behavior of Gases
16.3
Pressure
This collection of forces, caused by the collisions of the particles, pushes the walls of the container outward.
If more air is pumped into the balloon, the number of air particles is increased.
This causes more collisions with the walls of the container, which causes it to expand.

4. Behavior of Gases
16.3
Pressure
Pressure is measured in a unit called Pascal (Pa), the SI unit of pressure, but we’ll use kPa, or kiloPascals.
At sea level, atmospheric pressure is kPa.
Unit for pressure = kPa

5. Behavior of Gases
16.3
Boyle’s Law
What happens to the gas pressure if you decrease the size (volume) of the container?
If you squeeze gas into a smaller space, its particles will strike the walls more often giving an increased pressure. The opposite is true, too.
Lower volume = higher pressure
Higher volume = lower pressure

6. Behavior of Gases
16.3
Boyle’s Law
Robert Boyle ( ), a British scientist, described this property of gases.
According to Boyle’s law, if you decrease the volume of a container of gas and hold the temperature constant, the pressure of the gas will increase.
An increase in the volume of the container causes the pressure to drop, if the temperature remains constant.

7. Behavior of Gases
16.3
Boyle’s Law
Boyle’s law states that as pressure is decreased the volume increases.
The opposite also is true, as shown by the graph.
As the pressure is increased, the volume will decrease.

8. Behavior of Gases
16.3
Boyle’s Law in Action
When Boyle’s law is applied to a real life situation, we can predict the new volume or new pressure of a gas mathematically.

9. Behavior of Gases
16.3
Boyle’s Law in Action
You can use the equation P1V1 = P2V2 to express this mathematically.
P1 = initial pressure (in kPa)
V1 = initial volume (in L)
P2 = new pressure (in kPa)
V2 = new volume (in L)

10. Example
15 L of gas has a pressure of 3 kPa. The pressure is increased to 5 kPa. What is the new volume of the gas?

11. Behavior of Gases
16.3
Charles’s Law
Jacques Charles ( ) was a French scientist who studied gases.
According to Charles’s law, the volume of a gas increases with increasing temperature, as long as pressure does not change.

12. Charles’s Law 16.3 As with Boyle’s law, the reverse is true, also.
Behavior of Gases
16.3
Charles’s Law
As with Boyle’s law, the reverse is true, also.

13. Behavior of Gases
16.3
Charles’s Law
Charles’s law can be explained using the kinetic theory of matter.
As a gas is heated, its particles move faster and faster and its temperature increases.
Because the gas particles move faster, they begin to strike the walls of their container more often and with more force.

14. Behavior of Gases
16.3
Using Charles’s Law
The formula that relates the variables of temperature to volume shows a direct relationship, V1/T1 = V2/T2, when temperature is given in Kelvin (pressure remains constant).
To convert from Celsius to Kelvin, simply add 273 to the Celsius temperature.
Example: 10̊C = 283 K

15. Behavior of Gases
16.3
Using Charles’s Law
What would be the resulting volume of a 2.0-L balloon at 25.0C that was placed in a container of ice water at 3.0C?

16. Behavior of Gases
16.3
Using Charles’s Law
As Charles’s law predicts, the volume decreased as the temperature of the trapped gas decreased.

17. The Pressure-Temperature Relationship
Behavior of Gases
16.3
The Pressure-Temperature Relationship
What happens if you heat an enclosed gas? The particles of gas will strike the walls of the canister more often. Why?
If the pressure becomes greater than the canister can hold, it will explode.
At a constant volume, an increase in temperature results in an increase in pressure.

18. Pressure and Temperature
Joseph Louis Gay-Lussac was a French professor who studied the behavior of gases with many scientists.
In the early 1800s, he observed a relationship between the pressure and temperature of gases.

19. Gay-Lussac’s Law
Just like Charles’ law, Gay-Lussac’s law describes a direct relationship between two variables (as one increases, so does the other).
According to the law, as the temperature of a gas increases, so does the pressure (as long as the volume remains constant). As the temperature decreases, so does the pressure (as long as the volume remains constant).

20. Mathematically speaking…
We can look at this law mathematically.
P1/T1 = P2/T2
P1 = initial pressure (in kPa)
T1 = initial temperature (in K)
P2 = new pressure (in kPa)
T2 = new temperature (in K)

21. Example
A gas in an aerosol can has a temperature of 30̊C and a pressure of 3 kPa. If the temperature is increased to 45̊C, what will the new pressure of the gas be?
Don’t forget to convert ̊C to K first. 

22. Section Check
16.3
Question 1
What would be the resulting volume of a 3.0-L balloon at 25.0º C that was placed in a container of ice water at 4.0º C, if pressure is constant?
A L
B L
C L
D L

23. Section Check
16.3
Answer
The answer is A. Use the formula that relates volume to temperature given in Kelvin, V1/T1 = V2/T2. In this case, V1 = 3.0 L, T1 = 25.0º C = 298º K, T2 = 4.0º C = 277º K. Solving for V2 gives 2.8 L.

24. Section Check
16.3
Question 2
The SI unit of pressure is the pascal, but we use the _________.
A. coulomb
B. tesla
C. Watt
D. kiloPascal

25. Section Check
16.3
Answer
The answer is D. The SI unit of pressure is the Pascal; we measure pressures in kiloPascals.