1. Gas Laws

2. The Gas Laws are mathematical
The gas laws will describe HOW gases behave.
Gas behavior can be predicted by the theory.
The amount of change can be calculated with mathematical equations.
You need to know both of these: the theory, and the math

3. Variables for Gas Laws P=pressure V=volume T=temperature
n=number of moles
R=gas constant

4. Units for Gas Laws P=pressure (mmHg, atm, torr, kPa)
V=volume (Liters or L)
T=temperature (Kelvin or K)
n=number of moles (mol)
R=gas constant (atm x L/mol x K)

5. Robert Boyle ( )

6. #1. Boyle’s Law
Gas pressure is inversely proportional to the volume, when temperature is held constant.
Pressure x Volume = a constant
Equation: P1V1 = P2V2 (T = constant)

7. Graph of Boyle’s Law
Boyle’s Law says the pressure is inverse to the volume.
Note that when the volume goes up, the pressure goes down

8. Jacques Charles ( )

9. #2. Charles’s Law
The volume of a fixed mass of gas is directly proportional to the Kelvin temperature, when pressure is held constant.
This extrapolates to zero volume at a temperature of zero Kelvin.

10. Graph of Charles’ Law
Charles’ Law says the volume is proportional to the temperature.
Note that when the volume goes up, the temp goes up

11. Converting Celsius to Kelvin
Gas law problems involving temperature will always require that the temperature be in Kelvin. (Remember that no degree sign is shown with the kelvin scale.)
Kelvin = C + 273
°C = Kelvin - 273
and

12. Converting pressure 1 atm = 760 mmHg 1 atm = 760 torr
1 atm = kPa

13. Converting grams to moles
1 mole = molar mass in grams

14. Joseph Louis Gay-Lussac (1778 – 1850)

15. #3. Gay-Lussac’s Law
The pressure and Kelvin temperature of a gas are directly proportional, provided that the volume remains constant.
How does a pressure cooker affect the time needed to cook food?

16. Graph of Gay-Lussac’s Law
Gay-Lussac’s Law says the pressure is proportional to the temperature.
Note that when the pressure goes up, the temp goes up

17. #4. The Combined Gas Law
The combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas.

18. The combined gas law contains all the other gas laws!
If the temperature remains constant... P1 x V1 P2 x V2 = T1 T2
Boyle’s Law

19. P1 x V1 P2 x V2 = T1 T2 Charles’s Law
The combined gas law contains all the other gas laws!
If the pressure remains constant... P1 x V1 P2 x V2 = T1 T2
Charles’s Law

20. P1 x V1 P2 x V2 = T1 T2 Gay-Lussac’s Law
The combined gas law contains all the other gas laws!
If the volume remains constant... P1 x V1 P2 x V2 = T1 T2
Gay-Lussac’s Law

21. 5. The Ideal Gas Law #1 R = 0.0802 (L x atm) / (mol x K)
Equation: PV = nRT
Pressure times Volume equals the number of moles (n) times the Ideal Gas Constant (R) times the Temperature in Kelvin.
R = (L x atm) / (mol x K)

22. The Ideal Gas Law
We now have a new way to count moles (the amount of matter), by measuring T, P, and V.
P x V
R x T
n =

23. Ideal Gases
We are going to assume the gases behave “ideally”- in other words, they obey the Gas Laws under all conditions of temperature and pressure
An ideal gas does not really exist, but it makes the math easier and is a close approximation.
Particles have no volume? Wrong!
No attractive forces? Wrong!

24. Ideal Gases
There are no gases for which this is true (acting “ideal”); however,
Real gases behave this way at a) high temperature, and b) low pressure.
Because at these conditions, a gas will stay a gas!