1. Gases
Gas Laws

2. Boyle’s Law
The pressure and volume of a gas are inversely related -at constant mass & temp P V
P1 × V1 = P2 × V2

3. Example Problems pg 335 # 10 &11
10. The pressure on 2.50 L of anesthetic gas changes from 105 kPa to 40.5 kPa. What will be the new volume if the temp remains constant?
P1 = 105 kPa P2 = 40.5 kPa
V1 = 2.5 L V2 = ?
P1 × V1 = P2 × V2
(105) (2.5) = (40.5)(V2)
262.5 = 40.5 (V2)
6.48 L = V2

4. Example Problems pg 335 # 10 &11
11. A gas with a volume of 4.00L at a pressure of 205 kPa is allowed to expand to a volume of 12.0L. What is the pressure in the container if the temp remains constant?
P1 = 205 kPa P2 = ?
V1 = 4.0 L V2 = 12.0 L
P1 × V1 = P2 × V2
(205) (4.0) = (P2)(12)
820 = (P2) 12
68.3 L = P2

5. Charles’ Law
The volume and temperature (in Kelvin) of a gas are directly related
at constant mass & pressure
V1 = V2 T T2 V T
***Temp must be in Kelvin
K = °C + 273

6. Example Problems pg. 337 # 12 & 13
12. If a sample of gas occupies 6.80 L at 325°C, what will be its volume at 25°C if the pressure does not change?
V1= 6.8L V2 = ?
T1 = 325°C = 598 K T2 = 25°C = 298 K
6.8 = V2
598 × V2 =
V2 = 3.39 L

7. Example Problems pg. 337 # 12 & 13
13. Exactly 5.00 L of air at -50.0°C is warmed to 100.0°C. What is the new volume if the pressure remains constant?
V1= 5.0L V2 = ?
T1 = -50°C = 223 K T2 = 100°C = 373 K
5 = V2
(223) V2 = 1865
V2 = 8.36 L

8. Gay-Lussac’s Law P1 = P2 T1 T2
The pressure and absolute temperature (K) of a gas are directly related
at constant mass & volume
P1 = P2
T T2 P T
***Temp must be in Kelvin
K = °C + 273

9. Example Problems
1. The gas left in a used aerosol can is at a pressure of 103 kPa at 25°C. If this can is thrown onto a fire, what is the pressure of the gas when its temperature reaches 928°C?
P1= 103 kPa P2 = ?
T1 = 25°C = 298 K T2 = 928°C = 1201 K
103 = P2
298 × P2 = 123,703
P2 = 415 kPa

10. Example Problem pg. 338 # 14
14. A gas has a pressure of 6.58 kPa at 539 K. What will be the pressure at 211 K if the volume does not change?
P1= 6.58 kPa P2 = ?
T1 = 539 K T2 = 211 K
= P2
539 × P2 = 1388
P2 = 2.58 kPa

11. P1V1 T1 P2V2 T2 = Combined Gas Law Combines the 3 gas laws as follows:
The other laws can be obtained from this law by holding one quantity (P,V or T) constant.
Use this law also when none of the variables are constant.

12. How to remember each Law!
Fizz Keepers
Gay-Lussac P T
Boyles
Charles
Balloon and flask Demo
Cartesian Divers V

13. P1V1 T1 n P2V2 T2 n = Ideal Gas Law
The 4th variable that considers the amount of gas in the system is
Equal volumes of gases contain equal numbers of moles (varies directly w/V).
Add moles to the combination gas law
P1V1
T1 n =
P2V2
T2 n

14. UNIVERSAL GAS CONSTANT
Ideal Gas Law
You can calculate the # of n of gas at standard values for P, V, and T PV Tn
= R
(1 atm)(22.4L)
(273K)(1 mol)
= R
UNIVERSAL GAS CONSTANT
R= atm∙L/mol∙K
R=8.315 kPa L/molK
You don’t need to memorize this value!

15. UNIVERSAL GAS CONSTANT
Ideal Gas Law
PV=nRT
UNIVERSAL GAS CONSTANT
R= atm∙L/mol∙K
R=8.315 kPa L/molK
You don’t need to memorize these values!

16. Example Problems
1. At what temperature will 5.00g of Cl2 exert a pressure of 900 mm Hg at a volume of 750 mL?
2. Find the number of grams of CO2 that exert a pressure of 785 mm Hg at a volume of 32.5 L and a temperature of 32 degrees Celsius.
3. What volume will 454 g of H2 occupy at 1.05 atm and 25°C.