Chapter 5

Gas Laws

Scuba Diving

Dive Belize

Air…

• The atmosphere is

Diving Issues• Nitrogen Narcosis

– Nitrogen narcosis is a condition that occurs in divers breathing compressed air. When divers go below depths of approximately 100 ft, increase in the partial pressure of nitrogen produces an altered mental state similar to alcohol intoxication.

The Bends• Decompression sickness• nitrogen from the air will dissolve in the

water in his or her body. If the diver were to swim quickly to the surface, it is just like uncorking a bottle of soda -- the gas is released. This can cause a very painful condition, and it is sometimes fatal.

Increased pressure

• The pressure on divers increases by one atmosphere for every 33 feet of depth

• At 100 feet, some people say it is difficult to breathe

Decompression

• If divers do not decompress as they surface, they can develop the bends.

• Stops at various intervals as they rise to the surface, sometimes for 15 to 20 minutes or more.

Pressure

• Defined as the force per area

• Equation:

How is pressure measured?

• Barometers

• Manometers p 123, fig 5.2

• Units:

Gas Properties

•

• The physical volume of the molecules is negligible compared to the container

•

Gas Properties

•

• Average kinetic energy is related to the absolute temperature

The Gas Laws

• Boyle’s

• Charles’

• Guy-Lussac’s

• Avogadro’s

• Combined

• Ideal

• Molecular mass

• Dalton’s partial pressures

Boyle’s

• Relates pressure and volume

• Equation:–

• Temperature and number of molecules fixed

–

Charles’

• Relates volume and temperature

• Equation:–

• Pressure and number of molecules fixed

–

Guy_Lussac’s

• Relates Pressure and Temperature

• Equation– P/T = Constant

• Volume and number of molecules fixed

–

Avogadro’s

• Relates number of molecules and volume

• Equation– V/n = constant

• Pressure and temp are fixed

–

Combined

• Relates P, V, and T

• Equation– PV/T = constant

– Number of molecules is fixed

–

Ideal Gas Law

• Combines all of the above

• Equation:–

– Use Standard Temperature and Pressure,

Molecular Mass

• Determine the molar mass of a gas

• n = g/M

• n = PV/RT

• g/M = PV/RT

• M = gRT/PV

Dalton and Partial Pressure

• Ptotal = P1 + P2 + …

Henry’s Law

• Relates solubility and pressure

• Equation:

Volume gas dissolved

Volume of liquid

= CH x Pg

Practice

• What is the volume of 2.40 moles of O2 under a pressure of 5.00 atm at a temperature of 755 K?