Gas Laws

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

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.

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.

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

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+460 55F+460 40FT3 = V2 538 515 20600 =538V2 38.29FT3 = V2

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.

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+460 115F+460 3014.7PSI = P2 538 575 1733452.5 = 538P2 1733452.5/538 = P2 3222 PSI =P2

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 T1 T2 Absolute pressure and absolute must be used.

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?

Step 1 Determine Absolute Values 1ata V1 = 95 ft3 T1 = 84F + 460 = 544R P2 = (112ffw / 34ffw) + 1atm = 4.29 ata V2 = Unknown T2 40F + 460 = 500R

Apply the General Gas Law P1V1 = P2V2 T1 T2 1ata x 95 ft3 = 4.29 ata x V2 544R 500R V2 = 1ATA x 95FT3 x 500R 4.29ata x 544R V2= 47500 / 2333.76 = 20.35 ft3

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

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?

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