Unit 2: Gas Laws PPT

Gram molecular weight

gmw

Diffusion

D

Density weight

dw

Mass

n

Pressure

P

Volume

V

Temperature

T

The gas constant

R

Constant

K

An understanding of the gas laws is important in the practice of respiratory care. During....

mechanical ventilation, volumes, pressures, flows and the temperature of the gas delivered to a patient are routinely manipulated to better match changes with patient's condition.

It is important to be able to predicthow these changes affect

gas delivery to a patient.

Kinetic Molecular Theory

explains macroscopic properties of gases, such as pressure, temperature, viscosity, density, thermal conductivity and volume by considering their molecular composition and motion

How much energy is lost during molecular collisions?

No energy is lost

The volume of molecules is

negligible(quantity is so small it doesn't matter)

No forces of mutual attraction....

existbetween molecules (bounce off each other)

Avogadro's Law

Equal volume of gasses at the sametemperature and pressure must containthe same number of moles, atoms, ions.

Avogadro's Law: This number is

6.023 x 10 to the 23rd

- This is ONE mole (gram molecular weight)of gas

Avogadro's Law: Thus one mole of gas, at a constant temperature and pressure, should occupy

the same volume as one mole on any gas.

Avogadro's Law: Density of gas =

Density of gas = gram molecular weight (gmw)/ Universal molar volume(22.4) (CO2 22.3)

Density of gas mixture can be calculated =

the sum of the % of each gas in a mixture must be known: dw of air = (%N2 x gmw) + (% O2 xgmw) / 22.4

Formula: v/n =k

Avogadro's Comparison: Comparison illustratingAvogadro's hypothesis.

Note that argon gas consists of argon atoms.Each gas has the same volume, temperature, and pressure and thus contains the same number of molecules.Because a molecule of one substance differs in mass from a molecule of another, the masses of gas in the three containers differ

Example: A helium balloon weighs much less than a balloon filled with Oxygen

the lighter gas has as less # of moles

Example: Lungs expand as they fill with air. Exhaling...

decreases thevolume of the lungs

Example: Administering low density gas mixture too vercome upper airway obstruction, lighter gas with less moles can...

get pastthe airway obstruction

Atmospheric pressure is caused by

by the weightof the atmosphere pushing down on itselfand the surface of earth

Low-pressure areas have

less atmosphericmass above their location, whereas high-pressure areas have more atmospheric mass.

as elevation increases (high altitude), there is less overlying atmospheric mass, so the pressure

decreases with increasing elevation.

Although the level of O2 (21%) & N2 (79%)remains the same, the air density level itself, the number of molecules of gas in the atmosphere is what ....

decreases whenaltitude increases & ultimately effects ourability to oxygenate

An increase in Oxygen is used in certain circumstances not because

there is less oxygen, but to increase partial pressure in the blood.

The pressure exerted by a single gas inmixture is called its

partial pressure

Dalton's Law: Relationship among partial pressure and total pressure in a gas mixture. The total pressure of a mixture of gases must equal

the sum of partial pressures of all component gases.

The partial pressure of each gas mixture is the pressure it would exert if

it occupied the entire volume alone.

The partial pressure exerted by eachconstituent gas is

proportional to its volumetric percentage of the mixture

Ptotal = P1 + P2 + P3

Pgas = %gas X Ptotal

Example: As you go up a mountain, the air becomes less compressed and is therefore thinner. Although the percentage of oxygen is the same, the thinner air means

it feels like there is less oxygen to breath.

Example: Mountain climbers need supplemental oxygen at high altitudes for this reason. By increasing Oxygen,

we raise the partial pressure and increase uptake to the lungs

Example: Hyperbaric chamber(dropping under sea level to

increaseblood oxygenpartial pressure(PO2).

Hyperbaric oxygen therapy is conducted at pressures between

4 to 6 atm

Bubble reduction: what law?

(Boyle's law)

Hyperoxygenation of blood and tissue: what law?

(Henry's law)

Up to 6 atmosphere's

(Daltons Law)

Diffusion is the process whereby molecules move from areas of

high concentration to areasof lower concentration.

Gases have ____ kinetic energy, they diffuse most rapidly, this is the driving force behind diffusion of gases

High

Diffusion occurs in gases, liquids and is responsible for gas exchange in and out of lungs/tissues O2 and CO2 must sometimes move

through significant barriers

Graham's Law: Mathematically the rate of diffusion of a gas(D) is

inversely proportional to the square root of the gram molecular weight of the gas

Diffusion (through gas) = 1/√gmw Lighter gases diffuse rapidly, whereas heavy gases diffuse more slowly.

Example: Given 2 gases, where gas A has a higher concentration than Gas B, Gas A will

diffuse more rapidly than gas B due to its higher concentration

Effusion

is the escape of gaseous molecules through as mall (usually microscopic) hole, such as a hole in a balloon

- This process wasused using uranium increation of the atomicbomb during WWII

Fick’s Law: The bulk movement of a gas through biological membrane (Vgas) is Fick’s law of diffusion. The rate of diffusion of a gas depends...

on the surface area, thickness of the membrane, diffusion properties of the gas and partial pressure gradient across the membrane.

Fick's Law of Diffusion

Describes oxygen transport to the lungs

Effective gas exchange depends on:

Large surface area in the lungs (approx. 100 sq. meters)

Thin membrane between air and blood

These conditions enable efficient diffusion of gases

Fick's Diffusion Transport - Key Concepts

Diffusion increases with:

Greater surface area

Higher diffusion constant (depends on type of gas)

Larger pressure gradient

Diffusion decreases with:

Greater membrane thickness or distance

These factors determine the diffusing capacity of the lungs, especially in disease conditions

Henry's Law

At a constant temperature, the amount of a givengas that dissolves in a given type of liquid isdirectly proportional to the partial pressure (PP)

As the kinetic energy of the gaseous solute increases, its molecules have a greater tendency to escape the attraction of the solvent molecules and return to the gas phase. Therefore

the solubility of a gas decreases as the temperature increases

Henry's Law predicts how gasses behave during

gas exchange in liquids based onthe partial pressure gradients (difference between PP of gases and dissolved coefficients) and solubility of oxygen and carbon dioxide

Increasing temperature , increase kinetic energy, releases more molecules

into theair, therefore decreasing solubility

Patient has very high body temperature is given a

coolingblanket to bring down temperature and increase blood solubility

Underwater Diving

solubility of gases increase with depth the body tissues take on more gas over until saturated. To avoid injury the diver must ascend slow enough that the excess dissolved gas is carried away by the blood and released into the lung gas and doesn't cause decompression sickness.

Boyle's Law

Relates volume of gas to its pressure. With the temperature constant, the volume of gas varies inversely with the pressure. During Isothermal conditions, the temperature of an ideal gas should not change with either expansion or contraction.

Charles Law

The volume of gas varies directly with changes in temperature. As the temperature increases the volume of gas also will increase..& opposite holds true too..temperature decease = volume decrease

Example: Atmospheric pressure remains the same, when air is heated it will expand and therefore become less dense.

Therefore, hot air rises and so do Hot air balloons

Example: In PFT labs all volumes collected from patients must be corrected for temperature. Exhaled air is

smaller than the volume it occupied in the lungs due to decrease in temperature at which the exhaled volume was measured.

Gay-Lussac's Law

- Describes the relationship between pressure and temperature of a gas.

- The pressure exerted by a gas varies directly with its absolute temperature.

- As temperature increases pressure will increase as long as volume is constant.

Combined Gas Law

Whenever we hear combined gas law it is a combination of Boyle's, Charles' and Gay-Lussac's law. It is useful in determining pressure, volume or temperature changes

Ideal Gas Law

involves a combination of Boyle's, Charles's, Gay Lussac's and adds Avogadro's (gmw) resulting in the Ideal Law.