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Gases Boyles Law Amontons Law Charles Law ∴ Combined Gas

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Gases Boyles Law Amontons Law Charles Law ∴ Combined Gas Gas Physics FICK’S LAW Adolf Fick, 1858 Properties of “Ideal” Gases Fick’s law of diffusion of a gas across a fluid membrane: • Gases are composed of molecules whose size is negligible compared to the average distance between them. Rate of diffusion = KA(P2–P1)/D – Gas has a low density because its molecules are spread apart over a large volume. • Molecules move in random lines in all directions and at various speeds. Wherein: – The forces of attraction or repulsion between two molecules in a gas are very weak or negligible, except when they collide. K = a temperature-dependent diffusion constant. – When molecules collide with one another, no kinetic energy is lost. A = the surface area available for diffusion. • The average kinetic energy of a molecule is proportional to the absolute temperature. (P2–P1) = The difference in concentraon (paral • Gases are easily expandable and compressible (unlike solids and liquids). pressure) of the gas across the membrane. • A gas will completely fill whatever container it is in. D = the distance over which diffusion must take place. – i.e., container volume = gas volume • Gases have a measurement of pressure (force exerted per unit area of surface). – Units: 1 atmosphere [atm] (≈ 1 bar) = 760 mmHg (= 760 torr) = 14.7 psi = 0.1 MPa Boyles Law Amontons Law • Gas pressure (P) is inversely proportional to gas volume (V) • Gas pressure (P) is directly proportional to absolute gas • P ∝ 1/V temperature (T in °K) ∴ ↑V→↓P ↑P→↓V ↓V →↑P ↓P →↑V • 0°C = 273°K • P ∝ T • ∴ P V =P V (if no gas is added/lost and temperature is held constant) 1 1 2 2 ∴ ↑T→↑P ↑P→↑T ↓T →↓P ↓P →↓T • ↓V → also ↑density • ∴ P1/T1=P2/T2 (if no gas is added/lost and volume is held constant) Charles Law ∴ Combined Gas Law • Gas volume (V) is directly proportional to absolute gas • Combining Boyles, Amontons & Charles Laws: temperature (T in °K) • 0°C = 273°K • ∴ P V /T = P V /T (if no gas is added/lost) • V ∝ T 1 1 1 2 2 2 • P = initial pressure ∴ ↑T→↑V ↑V→↑T ↓T →↓V ↓V →↓T 1 • V1 = initial volume • T = initial absolute temperature • ∴ V1/T1=V2/T2 (if no gas is added/lost and pressure is held constant) 1 • P2 = final pressure • V2 = final volume • T2 = final absolute temperature • Ideal Gas Law: PV=nRT • n = total number of gas molecules in the vessel • R = constant Heyer 1 Diving Physiology Gas Exchange: notes Carbon dioxide (0.03%) Argon (0.93%) Oxygen (20.95%) Partial Pressure (PO2) ~ 0.2 atmospheres Pressure of ” Gas Exchange Nitrogen (78.09%) Partial Pressure (PN2) ~ 0.8 atmospheres 1.0 Atmosphere Total Pressure diving 1Atmosphere “ Air (gases) in our atmosphere are heavy and put pressure on us Diving: potential hazards Why seals can dive so long Push balloon 10 m Balloon shrinks to half its size at surface! Partial Pressure (P ) ~ 0.4 atmospheres underwater O2 (and avoid the hazards) Partial Pressure (PN2) ~ 1.6 atmospheres 2.0 Atmospheres Total Pressure 2 Atmospheres 2 Pressure of Gases can diffuse (spread out to less- 10 meters concentrated places) and dissolve in water. Water is heavy and increases Concentration/ pressure/compresses gasses. High Partial Pressure Also note: When carbon dioxide (CO2) dissolves in Low Concentration/ water, it creates an acid (carbonic acid lower pH). Partial Pressure Free diving & Regulation of the drive to breathe shallow-water blackout Free diving = breath-hold diving Hyperventilate → ↓P in blood → you don’t feel CO2 the need to breathe → dive long & deep. Diving →↑depth →↑P , so you extract more O O2 2 from air. With low P in blood, you still don’t feel the need CO2 to breathe. Ascent →↓depth →↓↓P . O2 ↓P in blood to brain → loss of consciousness Increasing P decreases pH, O2 CO2 stimulating you to breathe c.f., Fig. 42.28 SCUBA: self-contained underwater SCUBA: self-contained underwater breathing apparatus breathing apparatus Decompression Sickness (Bends) Air Embolism SCUBA: breathing air at ambient pressure SCUBA: breathing air at ambient pressure At depth, lungs filled with air at high pressure At 30 meters depth, your whole body feels a pressure of 4 atm (1+3) -- including the air in Ascent →↓depth →↓total pressure. your lungs. ↓P →↑V Diving →↑depth →↑P . N dissolves in tissues. If holding your breath, lung volume N2 2 overexpands Ascent →↓depth →↓P (decompress). N2 Alveoli rupture → air bubbles into bloodsream N2 tissues comes out of solution → microbubbles. If enough microbubbles form, may collect in Bubbles may lodge in tissues & small vessels tissues & small vessels causing bends. causing stroke, heart attack, etc.. Heyer 1 Diving Physiology SCUBA: self-contained underwater breathing apparatus Marine Mammal The 3 Rules! Diving Physiology Don’t panic! You brought air with you — no need to rush Stop! — Breathe! — Think! Never hold your breath! if breathing compressed air Ascend slowly! Allow your body to adapt gradually Why can they dive so much better than us? California sea lion Elephant seal dives: Elephant Seals Telemetry tagged study Elephant seal dives: It’s not in the lungs Swim 90 km/day Underwater 90% of time Ave. dive = 24 min — max 2 hr Lung volume ≈ 4.6% of — with 2.5 min surface intervals body volume for all Dives ave. 400+ meters — max 1500 mammals -- including meters marine mammals. Marine mammals don’t rely on the air in their lungs while underwater. Heyer 2 Diving Physiology Use oxygen slowly: Marine mammals have The Diving Reflex: 2 kinds of tricks: Heart rate slows Use oxygen slowly. Blood pressure decreases Store a lot of oxygen. Peripheral circulation decreases Spleen shrinks: more blood into circulation Store a lot of oxygen: Why can they dive so much better than us? Large blood volume Why don’t they get High concentration of red cells air embolisms? Why don’t they get High concentration of hemoglobin in red cells the bends? High concentration of Why don’t they get myoglobin in muscle shallow water blackout? Heyer 3 c.f., Fig. 42.29 O2 & CO2 diffuse from high concentration to low concentration. .
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