"We live submerged at the bottom of an ocean of air - Torricelli, 1644"
Dr.J.Edward Johnson.M.D., D.C.H.,
Asst. Professor
Kanyakumari Govt Medical College & Hospital,
Asaripallam, Nagercoil,
Tamilnadu, INDIA.
Molecular Theory
Van der Waals forces
Lattice
(oscillates)
•All matter is made of tiny particles called atoms.
•These atoms are in constant motion Brownian motion (random motion).
• Each particle has kinetic energy.
• Collisions between particles are perfectly elastic.
Interface
Pressure
Saturated Vapour Pressure
The Gas Laws
Introduction
1. Definitions:
Pressure = force/area
P = F/A
2. Units:
• Pascal (Pa): 1 Pa = 1 Newton/m2 or 1N/m2
The Pascal is the Standard International Unit of pressure
The Newton is the Standard International Unit of force
•Atmosphere (atm): one atm =101325 Pa
•Pounds per sq inch (psi): one atm = 14.7 psi or lbs/in2
•Torricelli (torr): one atm = 760 torr
mmHg: 1 mmHg = 1 torr
•Millimeters Hg: one atm = 760 mmHg
1 atm = 14.7 psi = 760 mmHg = 101 kPa
In the Torricellian tube, the atmospheric
pressure supports, mercury 760 mm tall
Pressure P= f/a
Pressure is inversely proportional to area
20ml
1 atm
10ml
2 atm
Pressure P= f/a
Anesthesia Machine Examples
 Pressure
Relief Valve
 Expiratory Valve
 Pressure-reducing valve
AKA pressure regulator
 Oxygen Failure warning device
Comparison of Variables & Constants in Gas Laws
Variables allowed to change
Variables held constant
Resulting relationship
Formal designation
Pressure and Volume
Number of molecules and
Temperature
P1V1 = P2V2
Boyle's Law
Volume and Temperature
Number of molecules and
Pressure
V1/T1=V2/T2
Charles' Law
Pressure and Temperature
Number of molecules and
Volume
P1/T1=P2/T2
Amonton's Law
Number molecules and
Volume
Pressure and Temperature
V1/n1=V2/n2
Avogadro's Law
Pressure, Volume, &
Temperature
Number of molecules
P1V1/T1=P2V2/T2
Combined Gas Law
P1V1/n1T1=P2V2/n2T2
Ideal Gas Law
Pressure, Volume,
Temperature & Number of
molecules
--
Boyle’s Law (Pressure – Volume Law)
The volume of a given amount of gas at a constant
temperature varies inversely with the pressure
P1V1 = P2V2
Graph of pressure vs. volume for a gas enclosed in
a cylinder at constant temperature (Boyle's law)
Example - Cylinders
For example, if we have a cylinder of gas under pressure equivalent to 13,800 kPa (the
internal volume or capacity of the cylinder is about 10 liters), how much gas would be
available at atmospheric pressure which we will say is about 100 kPa.
Cylinder
Atmosphere
P2 100 kPa
P1 13,800 kPa
V2
V1 10 liters
P1V1 = P2V2
13,800 x 10 = 100 x V2
V2 = 13,800 x 10
100
V2 = 1380 lts
?
Charles’ Law (Temperature-Volume Law)
Gas volume varies directly with
temperature at a constant pressure
V1/T1=V2/T2
Remember, always use degrees Kelvin
for temperature representation
Amontons' Law of Pressure-Temperature
Gas pressure varies directly with temperature
at a constant volume
P1/T1=P2/T2
Gay-Lussac Law
Law of combining volumes
The ratio between the volumes of the reactant gases and the
products can be expressed in simple whole numbers.
STP- 273.15˚ k(0˚C)
- 101kPas(760mmHg)
Pressure-Volume-Temperature
Relationships
“Pay TV Can Be Good”
Pay- Can Pressure constant-Charles
Temperature constant-Boyles
T - Be
V - Good Volume constant- GayLussac
Avogadro's Law
For a given mass of an ideal gas, the volume and amount (moles)
of the gas are directly proportional if the temperature and
pressure are constant.
Avogadro's Law
“Equal volumes of any two gases at the same temperature and pressure
contain the same number of molecules.”
V∝ n (at constant T and P)
One mole of any gas contains the same number of molecules
(Avogadro's number =6.02×1023)
Gram molecule H2
(mass of gas)
O2
Same number of molecules
in one gram molecule
H2O
2H2+O2=2H20
Ideal Gas Law (Universal Gas Law)
Under the same condition of temperature and pressure, equal volumes
of all gases contain the same number of molecules.
He
N2
O2
Calibration of Vaporizers
One mole of Gas
At STP
Mol.wt of Iso – 184.5
184.5 gm of Iso = 1 mol
O2
224 L
O2 + Isoflurane
Isoflurane
18.45gm
0.1 mol
2.24 L
2.24 = 1%
224
Calculation of volume of Nitrous Oxide gas
Mol. Wt of N2O - 44
1 mol = 44 gm
3.4kg
44 gm(1mol) occupies = 22.4 L
3400 gm occupies = 22.4 x 3400 = 1730 L
44
Combined gas law
The combined gas law is a gas law which combines Charles's law,
Boyle's law, and Gay-Lussac's law
Combined gas law
Dalton’s Law of Partial Pressures
The total pressure exerted by a mixture of gases is the
sum of their individual partial pressures
PARTIAL PRESSURE of AIR
Partial Pressure (mmHg)
Inhaled Alveolar Exhaled
GAS
Nitrogen
Oxygen
CO2
H2O
vapor
TOTAL
594.70
160.00
0.30
570
103
40
569
116
28
5.00
47
47
760
760
760
Ptotal = Pa + Pb + Pc + etc
Dalton’s Law of Partial Pressures
Entanox Cylinders
Dalton’s Law of Partial Pressures
• What is the partial pressures of O2 and N2O if you
are administering a ratio of 70/30?
• N20 70% X 760 mmHg = 532 mmHg
O2 30% X 760 mmHg = 228 mmHg
760 mmHg
• Would this differ if you were administering
anesthesia at Denver General Hospital?
• N20 70% X 630 mmHg = 441 mmHg
O2 30% X 630 mmHg = 189 mmHg
630 mmHg
Miami
Miami
= 760mmHg
= 14.7 psi Denver = 630mmHg
12.2 psi
Adiabatic heating and cooling
Adiabatic changes in temperature occur due to changes in
pressure of a gas while not adding or subtracting any heat
Cryoprobe – N2O or CO2
Critical Temperature
As the substance approaches critical
temperature, the properties of its gas and
liquid phases converge, resulting in only one
phase at the critical point
Critical Temp of N2O = 36.5˚C
Critical Temp of O2 = -119 ˚C