Mason Physics Behavior Of Gases 1

Front 1

**Points which may be taken for granted when dealing with gases

Back 1

1.No definite boundary and gases will fill the entire container.
2.Gases have low density for there are large spaces between molecules.
3.Gases exert a pressure which is the same on all sides of the molecules.
4.Gases are readily compressible for the distance between molecules permits it.
5.Gases are more quickly affected by temperature change than liquids or solids.
6.Gases mix freely with each other, although, their attraction for each other is negligible.
7.Gases diffuse according to their molecular weights and viscosity.
8.The kinetic energy of the molecule and the number of molecules will influence the pressure exerted by the gas.
9.Gases will move, even though the concentration in two areas may be the same. They do not need either filtration or osmotic pressure to move.

Front 2

Gases are all influenced by 3 things, what are they?

Back 2

pressure, volume and temperature

Front 3

Gases are more quickly affected by temperature change than liquids or solids. Why?

Back 3

Molecules are farther apart. Because there are not a lot of cohesive forces in gases. Solids have strong cohesive forces.

Front 4

T or F: You have a flask with gas in it...The pressure will be the same everywhere in the container.

Back 4

True.

Front 5

What is needed to compress gases?

Back 5

pressure

Front 6

Gases diffuse according to what?

Back 6

their molecular weights and viscosity.

Front 7

**Standard Conditions

Back 7

Temperature = 0˚C
Pressure = 760 mmHg = 1 atmosphere (sea level)

Front 8

If gases are under considerable pressure, they
are expressed in:

Back 8

pounds per square inch (psi) atmospheres - i.e. three atmospheres = 760 x 3 or 2280 mmHg

Front 9

Dealing with physiology, the pressure of a given gas may be referred to as tension - expressed in either:

Back 9

cm of H20 or mmHg

Front 10

**Atomic and molecular weight

Back 10

The atoms of an element possess an average mass which correspond to and is known as atomic weight of element. In the case of oxygen, the value 16 is assigned to the mass. The value assigned to the average mass of other elements is relative to the mass of the oxygen atom.
Carbon = 12
Hydrogen = 1.008
Nitrogen = 14

Front 11

**Combining two or more atoms of the same element or two or more atoms of different elements produce a

Back 11

molecule

Front 12

**The mass of a molecule is equal to

Back 12

the sum of the atomic weight of the atom composing the molecule.

Front 13

**The figure assigned to the mass of a molecule is referred to as

Back 13

the molecular weight of substance.

Front 14

**What is Gram Molecular Weight?

Back 14

Molecular weight is expressed in grams. (Gram molecular weight) The term mole is a short-hand way of indicating this quantity.

Front 15

**1 mole of 02 would weigh ___ grams - contains ____ moles and has a Vol of ____ L

Back 15

32, 6.02 x 10 ^23, 22.4

Front 16

**1 mole of N2O would weigh ___ grams - contains ____ moles and has a Vol of ____ L

Back 16

44, 6.02 x 10 ^23, 22.4

Front 17

**1 mole of C02 would weigh ___ grams - contains ____ moles and has a Vol of ____ L

Back 17

44, 6.02 x 10 ^23, 22.4

Front 18

T or F: 1 mole of gas always has 22.4 L and 6.02 x 10^23 particles.

Back 18

True

Front 19

What is the significance of the near identical molecular weight of N2O and CO2?

Back 19

Due to the near identical molecular weight of N20 and C02 , the ETC02 monitor is able to measure the partial pressure of N2 0 also.

Front 20

T or F: 32 gms of 02 and 44 gms of N20 has the same number of molecules.

Back 20

True. This is known as Avogadro's number.

Front 21

What is Avogadro's Number?

Back 21

6.02 x 10^23

Front 22

**Avogadro's Law states

Back 22

"equal volumes of gases under the same conditions of pressure and temperature contain the same number of molecules“

If there is an equal number of molecules, these molecules will also be of the same volume.

Front 23

Gram Molecular volume:
Under standard conditions, any or all gases of 1 gram molecular weight (1 mole) of each gas was contained in a flexible container, each mole of any different gas would distend the container ____ L.

Back 23

22.4 L

Front 24

**T or F: 22.4 liters of 02 will contain the same number of molecules as 22.4 L of cyclo-propane.

Back 24

True. This is why gases are measured in liters or milliliters.

Front 25

At standard condition 1 liter of oxygen weighs____ gm

Back 25

1.429 gm

32/22.4 = 1.429

1 mole of 02 - weighs 32 gms - vol= 22.4 L - contains n molecules

1 mole of N2 0 - weighs 44 gms - vol= 22.4 L - contains n molecules

1 mole of C3H6 - weighs 42 gms - vol= 22.4 L - contains n molecules

Front 26

Gram molecular weight of a solid or liquid if converted into its gaseous phase would occupy ____ liters.

Back 26

22.4

Front 27

2 liters of O2 and 2 liters of N2O– How much of the bombarding against the wall of the breathing bag is performed by a particular gas?

Back 27

Total pressure is 760 mmHg, this is 100% of gases, volume is 4 liters
2 L of O2 is ½ of 4 L or 50%; 50% of 760 mmHg is 380 mmHg
This part or percentage of the “whole” is termed PARTIAL PRESSURE

Front 28

Molecular Motion Means?

Back 28

Molecules are in constant motion.

Molecular motion increases as energy is added and decreases as energy is removed.

Front 29

What is cohesion?

Back 29

Force of attraction between like molecules. Molecule of solids and liquids are held together by the force of cohesion.
Force is greatest in solids, less in liquid and least in gases.

Front 30

Cohesion influences what?

Back 30

the boiling points of liquids, their vapor pressure, viscosity, and surface tension, and the heat of vaporization (of anesthetics).

Front 31

What is adhesion?

Back 31

Attraction between unlike substances.
One particular application of adhesion is that of capillary action, where water or other fluid can be drawn up a cloth-like dissimilar material.
This phenomenon can be seen when blood spreads up a surgical drape or towel.
It also is the principle that allows for use of a “wick” to pick up liquid anesthetic in draw-over vaporizers.

Front 32

What is Surface Tension?

Back 32

At a liquid-gas (air) interface, liquid molecules are pulled together by forces created by unequal intermolecular stresses. Cleaning agents work in part by altering water’s surface tension.

Front 33

Discuss the general behavior of gases.

Back 33

Molecules of gases are moving in space with huge velocity, they collide with each other and strike walls of the containing vessels.

If volume is increased molecular impact of a given area decreases and pressure decreases

Front 34

What is Boyle's Law?

Back 34

Law of Pressure:
Robert Boyle - English physicist - 1662.

Relation of volume and pressure of gas when temperature is constant.

The volume of a gas at constant temperature is inversely proportional to the pressure
PV = K or (P1)(V1) = (P2)(V2)

Front 35

T or F: If volume is increased, molecular impact of a given area increases and pressure increases

Back 35

False: If volume is increased, molecular impact of a given area decreases and pressure decreases. There is an inverse relationship too, so decreased vol = increased pressure.

Front 36

Apply Boyle's Law to an e cylinder and breathing

Back 36

If a full E cylinder (small volume) of O2 is emptied slowly (so temperature does not change) 660 liters (large volume) will be released into the atmosphere
Full E cylinder of O2 ≈ 2100 psi
Squeezing the ambu bag increases pressure & decreases the volume
During inspiration, intrapulmonary pressure falls as volume increases. During expiration, intrapulmonary pressure increases as volume decreases

Front 37

**Boyle's Law: The volume of a gas at constant temperature is inversely proportional to the _______

Back 37

Pressure

Front 38

What is an ideal gas?

Back 38

Highly rarefied gas, that is, one in which the molecules are extremely far apart, there is no attraction between the molecules.

A gas assumed to exist under conditions in which there is not attraction between the molecules is referred to as an Ideal Gas.

Actually, ideal gases do not exist.

Front 39

What is the significance of Avagadro's Law?

Back 39

Avogadro advanced his postulate which stated that equal volumes of different gases under the same conditions of temperature and pressure contain equal numbers of molecules.

When a gas is expressed in terms of moles, rather than some other unit, there is, then, a constant which can be derived and is the SAME for all gases.

Front 40

**Ideal Gas Law Formula

Back 40

PV = nRT
Where P = pressure,
V = volume,
n = number of moles of gas (mole = gram molecular weight),
R = gas constant, and
T = temperature in Kelvin degrees.

Front 41

What is Atmospheric Pressure (Barometric Pressure)?

Back 41

The molecules of the gases composing the atmosphere exert a pressure on all earthly surfaces.

In addition, the atmosphere has weight.

The molecules close to the surface of the earth are compressed by those above them.

Front 42

One atmospheric pressure (1atm) = ________ mmHg

Back 42

760 mmHg (76 CmHg)

If pressure is expressed in weight per unit area-
- One atm = 14.7 lb/inch² (1033 gm\inch)

* 1 CmHg = 13.6 CmH20
1 Cm H2 0 = 0.7 mmHg

Negative when subatmospheric.
Positive when above atmospheric

Front 43

Tension: In clinical anesthesia pressure of great magnitude are expressed in ___

Back 43

psi. (e.g. 10 psi = 10 x 14.7 = 147 psi)

Gas pressure, particularly in physiology and pharmacology, are frequently referred to as tension.

They are expressed in cm of H20 or mmHg because of their small magnitude.

Front 44

Pressures of magnitude less than those of atmosphere are referred as ______ pressure. Those which are greater than atmospheric pressure as ______pressure.

Back 44

negative, positive

Front 45

Gas pressure, particularly in physiology and pharmacology, are frequently referred to as _____

Back 45

tension

Front 46

Charles' Law (1787 Jacques Charles)

Back 46

Volume of gas, provided the pressure remains constant, is directly proportional to its absolute temperature.

Heating a substance increases molecular movement and in the case of gas, there is a tendency to expand.
- Rationale of using heated vaporizers with desflurane

V/T = K or V1/T1 = V2/T2

Front 47

What is the relationship of Charles' Law to Kelvin?

Back 47

Charles in 1787 found experimentally that equal volume of gases kept at constant pressure expand by equal increment of volume for each degree centigrade rise in temperature.

The increment of increase for each degree is 1\273 of the volume of gas at 0◦C.

On the other hand for each degree of cooling there is lessened molecular activity and decrease of 1/273 of the volume at 0◦C for each degree fall in temperature.
With progressive cooling at a constant value, ultimately a point is reached at which molecular motion ceases.

In order to obtain cessation of molecular motion, the temperature must be reduced to -273 degree C or absolute zero (0◦C A).

At this point, theoretically, molecules should have no pressure, no volume.

Formula : T/ To = V / Vo

Example: If the temperature of a 273 ml vol. of gas at 0degC is raised 1deg C the volume becomes 274 ml. If the temp raised to 273 degree C, the resultant volume is doubled.

Front 48

Formula for converting K to C and C to K.

Back 48

K = C + 273
C = K - 273

Front 49

T or F: Most gases liquefy or are converted to solids long before temperatures reach to -273◦C.

Back 49

True.

Front 50

Take home: Charles Law

Back 50

temp and vol changes, pressure is the same.

Front 51

Take home: Boyle's Law

Back 51

as pressure changes, vol changes in the opposite direction: vol and pressure changes, temp stays the same.

Front 52

Apply Charles Law to an ETT in an autoclave.

Back 52

An ETT is placed in an autoclave. As the temperature increases, the cuff expands secondary to increasing volume.

**Remember pressure is constant.

Front 53

Vaporization of liquid anesthetics

Back 53

-these liquid drugs must be changed to vapor in order to become volatile anesthetic agents

-one milliliter of forane will expand to 195 cc's @ 238mmHg @ 20degC
-Halothane 226 cc's @ 243mmHg @ 20degC
-Ethrane 196 cc's @ 175mmHg @ 20degC
-Desflurane* 207 cc’s @ 664mmHg @ 20◦C
-Sevoflurane182 cc’s @ 160mmHg @ 20◦C

Front 54

**Gay Lussac's Law (1802) States?

Back 54

Volume of a gas remains constant, the pressure varies directly with the absolute temperature

P/T = K or P1/T1 = P2/T2

Front 55

Discuss Gay Lussac's Law

Back 55

Volume occupied by a given number of molecules of a gas at 0degC remains constant, but the temperature is varied, the pressure increases by 1/273 of the pressure at which it existed at 0degC.

Likewise, cooling causes a reduction of pressure by 1/273 of the pressure at 0degC.

This becomes practical when we visualize a cylinder with a compressed gas is stored next to a hot radiator.
The volume cannot expand, and no additional molecules are added, but the expanded and agitated molecules bombard the walls of the cylinder in proportion to the increase in temperature.
The temperature may become high enough to increase the pressure to the point of bursting (exploding) the container.
Formula: T/To = P/Po
(V is constant; T is absolute)

Front 56

**Take Home: Gay Lussac's Law

Back 56

if vol is constant and there is a change in temp, the pressure will have to change. (as add more heat, can support more pressure)

Front 57

Apply Gay Lussac's Law to N2O tank

Back 57

As a N2O tank empties, even though the liquid volume stays relatively constant, the pressure decreases moderately because of the temperature drop R/T the Joule-Thompson effect

When the tank is closed, the pressure is restored again until the liquid volume begins to decrease

Have to weigh the tank to determine how much is left.

Front 58

**General Gas Law:

Back 58

By combining the laws of Boyle, Charles, and Gay-Lussac, the following relationship can be written:

[(P1)(V1)] / T1 = [(P2)(V2)] / T2

Front 59

**Summarizes Boyle, Charles, and Gay Lussac's Laws

Back 59

Boyle’s Law-constant temp V↓P↑

Charles Law-constant pressure T↑V↑

Gay-Lussac’s-constant volume T↑P↑

Front 60

**Where knowing values for five of the terms, the sixth may be found. The values for T must be expressed in Kelvin degrees.

The general gas law for ideal gases has been modified for determining the effects of P, V, and T changes on real gases used in clinical practice.

On a test, five of six elements may be given and the examinee must solve for the remaining element.

What formula is used? What is important in solving correctly?

Back 60

The formula recommended to use:
*remember A is for absolute temperature*

P1 V1 A2 = P2 V2 A1
(or PVA 112 = PVA 221)

P1 = initial pressure
V1 = initial volume
A2 = new temperature (in Kelvin degrees)
P2 = new pressure
V2 = new volume
A1 = initial temperature (in Kelvin degrees)

Three things are important to solve these problems correctly:
(1) both volumes and both pressures have to be in the same measurements;
(2) all non-Kelvin degrees must be converted to that scale (or sometimes the answer must be converted to that scale; the A formula is to remind one that temperatures must be in the Kelvin scale); and
(3) the formula must be set correctly.

For example, finding P2 requires changing the formula to:
P2 = (P1 V1 A2) / (V2 A1)

Front 61

**Dalton's Law (Law of Partial Pressure): 1807

Back 61

Mixture of gases each exerts its pressure independently of the others.
The pressure exerted by one gas is called the Partial Pressure.
The total pressure exerted by a mixture of gases equals the arithmetical sum of the individual pressure exerted by each of the constituents of the mixture.
P = P1 + P2 + P3 + ...... PN

Front 62

Example of Dalton's Law:

Back 62

Air:
02 = 20.96% = 159.2 torr
N2 = 70.99% = 596.45 torr
C02 = 0.04% = 0.30 torr

P = 159.2 + 596.45 + 0.30 = 760

To get the torr x the % of the gas by 760...ie O2 21%,so .21 x 760 = 159

Front 63

Density of dry air

Back 63

1.3 gm/L but is usually stated as 1

Front 64

Density

Back 64

The weight of a liter of a gas or a vapor at standard condition is known as its Density.

Front 65

In case of solids and liquids, density is based upon

Back 65

the weight of a cubic centimeter (Cm3) of the substance at 0◦C

Front 66

Density of gas may be computed by dividing its molecular weight by gram molecular volume (22.4L). Give an example with O2.

Back 66

e.g. The density of 02 = 32/22.4 = 1.429 gm/L at 0degC

Front 67

Specific Gravity:

Back 67

Commonly used in clinical practice.

Specific gravity of a gas is the weight of unit volume of the gas compared to the weight of an equivalent volume of dry air under the identical condition of temperature and pressure.

Front 68

SG of Air. What is the General Formula?

Back 68

1
Specific gravity (S.G.) = molecular wt. of gas/ molecular wt of air (28.87)

In the case of solids and liquids S.G. is determined by comparing the weight of a unit volume of a substance with that of an equivalent volume of water. (Water being 1)

Front 69

SPECIFIC GRAVITIES OF GASES & VAPORS COMMONLY USED IN ANESTHESIA

Back 69

CARBON DIOXIDE.............1.5
NITROUS OXIDE..............1.53
OXYGEN.........................1.10
AIR...................................1.0
NITROGEN......................0.96
HELIUM..........................0.13
WATER VAPOR................0.6
HALOTHANE..................1.86*
ENFLURANE..................1.52*ISOFLURANE..................1.5*DESFLURANE...............1.45*
SEVOFLURANE.............1.50*

*S.G. is for liquid relative to H20

Front 70

Diffusion of Gases

Back 70

When a gas or a vapor is liberated into the space, the molecules quickly become distributed throughout the space until they completely fill it.

The passage of a gas from one place to another depends on molecular movement. The passage or movement is called diffusion.

Front 71

**The direction of diffusion is determined by differences in _______ ______ and not by any difference in amt of gas.

Back 71

partial pressure

Front 72

The passage of a gas from one place to another depends on molecular movement. The passage or movement is called _____

Back 72

diffusion

Front 73

A gas diffuses from a place where it is at ____partial pressure to one where it is at ____partial pressure.

Back 73

high, lower

This occurs even though at the point of lower partial pressure there is a larger volume of gas.