1. Gas Laws

2. Main Points Behavior of Gases Charles’ Law Amontons’ Law
The General Gas Law

3. Objectives
State Charles’ Law, express it as a working formula and discuss it’s application to scuba.
State Amontons’ Law, express it as a working formula and discuss it’s application to scuba.
State The General Gas law, express it as a working formula and discuss it’s application to scuba.

4. Volume and Temperature
Charles’ Law
The volume of a gas at constant pressure is directly proportional to the absolute temperature
V1 = V2
T1 T2
Can be used to approximate changes in the volume of gas available from a cylinder as the temperature changes.

5. Absolute Temperatures
Absolute temperature scales must be used in gas law calculations
When working in Farenheit add 460
Rankine scale
When working in Centigrade add 273
Kelvin Scale
Gay Lussac found that over the temperature range of 0-100oC, for each degree rise in temperature, gases expanded approximately 1/270th of the volume at 0oC

6. Charles’ Law Problem (English)
If a scuba cylinder delivers 40 ft3 of air at 78o F, how much
air is available at 55o F?
40 FT3 = V2
78F F+460
40FT3 = V2
20600 =538V2
38.29FT3 = V2

7. Amonton’s Law
The pressure of a gas at constant volume is directly proportional to the absolute temperature
P1 = P2
T1 T2
Can be used to calculate the changes in pressure in a cylinder as temperature changes.

8. Amontons’ Problem (Imperial)
A scuba cylinder contains 3,014.7 psia at 78o F.
What will be the pressure in a car trunk at 115o F?
3014.7PSIA = P2
78F F+460
3014.7PSI = P2
= 538P2
/538 = P2
3222 PSI =P2

9. General Gas Law Combines Boyle’s law, Charles’ law and Amontons’ law.
Predicts the behavior of any quantity of gas in terms of pressure, volume and temperature.
P1V1 = P2V2
T T2
Absolute pressure and absolute must be used.

10. Example At the surface, a cylinder contains 95 ft3 of
air at a temperature of 84F.
What volume of gas is available to the diver
at a depth of 112ffw and a temperature of
40F?

11. Step 1 Determine Absolute Values
1ata
V1 =
95 ft3
T1 =
84F = 544R
P2 =
(112ffw / 34ffw) + 1atm = 4.29 ata
V2 =
Unknown T2
40F = 500R

12. Apply the General Gas Law
P1V1 = P2V2
T T2
1ata x 95 ft3 = 4.29 ata x V2
544R R
V2 = 1ATA x 95FT3 x 500R
4.29ata x 544R
V2= / = ft3

13. Have We Covered: Behavior of Gases Charles’ Law Amontons’ Law
The General Gas Law

14. Can you
State Charles’ Law, express it as a working formula and discuss it’s application to scuba?
State Amontons’ Law, express it as a working formula and discuss it’s application to scuba?
State The General Gas law, express it as a working formula and discuss it’s application to scuba?

15. Last Thoughts
Understanding the gas laws allows you to anticipate phenomena such as variation in cylinder temperature with a change in temperature.