1. Gases obey Boyle's law, Charles' law, and Gay-Lussac's law, collectively known as the gas laws. 2. The ideal gas law combines these and states that for an ideal gas, pressure × volume divided by temperature is a constant (PV/T = nRT). 3. Dalton's law of partial pressures states that in a gas mixture, the total pressure is equal to the sum of the partial pressures of the individual gases.

1. Abdeljawad .M
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2. 2
•All matter is made of tiny particles called atoms.
•These atoms are in constant motion (random
motion).
• Each particle has kinetic energy.
• Collisions between particles are perfectly elastic.
Van der Waals forces
Lattice
(oscillates)
s

3. 3
VOLUME
Pressuretemperature

4. GAS LAWS
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5. 5
Boyle’s Law (Pressure – Volume Law)
The volume of a given amount of gas at a constant
temperature varies inversely with the pressure
V&1/P
PV=constant (k1)
V1P1=V2P2

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Graph of pressure vs. volume for a gas
enclosed in a cylinder at constant
temperature (Boyle's law)

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(Temperature-Volume Law)
Gas volume varies directly with
temperature at a constant pressure
V&T – V/T=constant(k3)-
Charles’ Law (Temperature-
Volume Law):

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Pressure-Temperature Law
Gay-Lussac’s Law: Gas pressure varies
directly with temperature at a constant
volume
P &T- P/T=constant-P1/T1=P2/T2

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for a given mass of a gas, at a constant:

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 A gas that completely obeys all three gas
laws.
Or
 A gas that contains molecules of infinitely
small size, which, therefore, occupy no
volume themselves, and which have no
force of attraction between them.
Perfect gas or ideal gas
Perfect gas:
No gas is ideal because under certain
conditions a gas may not obey the gas
laws.

11.  Combines the three gas laws
If PV = K1 , P/T = K2 and V/T = K3, then all can be
combined to give
PV/T = K
For 1 mole of a gas, K is named the universal gas
constant and given the symbol R = 8.32 joules /℃.
PV/T = R
For n moles of gas
PV/T = nR
so
PV = nRTThis equation is called the ideal gas law.
Or perfect gas law

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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
P1 13,800 kPa
V1 10 liters
P2
Atmosphere
100 kPa
V2 ?
P1V1 = P2V2
13,800 x 10 = 100 x V2
V2 = 13,800 x 10
100
V2 = 1380 lts

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 According secaned gas law, gases expand when
they are heated and, so become less dense.
Therefore, warm air tends to rise and this causes
convection currents.
One way of heat loss from the body is that air
next to body surface gets warmer and moves up
and thus our patient loses heat this way(esp.
paediatric anaesthesia)

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Medical gases are stored in clyinders having a constant
volume and high pressures (138 Barr in a full oxygen/air
cylinder). If these are stored at high temperatures, pressures
will rise causing explosions.
A full 02 cylinder is filled at 137 bar (absolute pressure)
at ambient temperature of 17 °C (i.e., 17 + 273 = -
~Kelvin). This cylinder is tested in the factory to withstand
pressure up to 210 bar. ‘when the temperature of the
cylinder is doubled (i.e., 290 x 2 = 580 Kelvin) e.g., when
the cylinder is accidentally dropped on a fire of an
incinerator, the pressure inside the cylinder will be
doubled (i.e., 137 _ = 274 bar) which exceeds the upper
limit of the cylinder; therefore, there will be a danger of
explosion.

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hydrogen thermometer
• In the hydrogen thermometer, when a constant volume of hydrogen is
heated, the pressure rises which be accurately recorded and gives an
indication of the absolute temperature.

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Note that , as the molecular wieghts of oxygen and hydrogen are
different. Thus, rather than express a quantity of gas in terms of mass . It
is more convenient to use a concept related to the number of molecules .
This is mole.
Mole = molecular weight in grams
A mole is the quantity of a substance that contains the same number of
particles as the number of atom in 0.012 kg of carbon 12 i.e., a mole
contains 6.022 x 1023 particles. This number is known as Avogadros
number. ‫الجسيمات‬ ‫عدد‬ ‫نفس‬ ‫على‬ ‫تحتوي‬ ‫التي‬ ‫المادة‬ ‫كمية‬ ‫هو‬ ‫المول‬
‫يحتويها‬ ‫التي‬12‫جرام‬‫من‬ ‫الكربون‬
( Mole = molecular weight in grams = 6.022 x
1023particles.)
(1mole of any gas at STP occupies 22.4
liters),
‫المول‬‫عن‬ ً‫را‬َّ‫ب‬‫ع‬ُ‫م‬ ‫للمادة‬ ‫الجزيئية‬ ‫أو‬ ‫الذرية‬ ‫الكتلة‬ ‫بأنه‬‫ها‬
‫بالجرام‬

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for example,
o MW of hydrogen (H2) is (1 x 2) i.e., 2, so its mole
equals 2 grams which occupy 22.4 liters at STP.
o MW of oxygen (02) is (16 x 2) i.e., 32, so its mole
equals 32 grams which occupy 22.4 liters at STP

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22. 3.4kg
Mol. Wt of N2O - 44
1 mol = 44 gm
44 gm(1mol) occupies = 22.4 L
3400 gm occupies = 22.4 x 3400 = 1730 L
44

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2kg
(2KG OF N2O Enough for 168 M)
Mol. Wt of N2O = 44
2 Kg Nitrous Oxide cylinder -----6L/M ----FOR HOW
LONG ??
N2=14*2=28
O=16
28+16=44
1 mol = 44 gm
2KG = ? Mol
2kg = 2000 gm
2000gm/44gm= 45 mol
1 mol = 22.4 L
22.4 * 45 = 1008 L
1008 / 6 = 168 M
Nitrous Oxide

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At constant volume and temperature, the total
pressure exerted by a mixture of gases is equal to the
sum of the partial pressures of the component gases.
Ptotal= P1+P2+P3……
Dalton’s Law of Partial Pressures

26. 1- Calculation of the partial pressure of a gas in a mixture:
For example;
• An Entonox cylinder consists of 50% N20 and 50% 02.
If the cylinder is emptied to an ambient pressur of 100 kPa,
the pressure inside the emptied cylinder i.e., 100 kPa = 50
kPa exerted by N20 + 50 kPa exerte; by Oz.
The partial pressure of one gas component = total pressure x
fractional concentration of each gas
• A compressed air cylinder consists of 79% N2 and 21% 02
(with ignoring the presence of other inert gases). If the
cylinder is compressed at a pressure of 100 bar, the
pressure exerted by.N, = 100 bar x 79/100 = 79 bar, the
pressure exerted by 02 = 100 bar x 21/100 = 21 bar.
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2-Manufacturing a cylinder containing
10%co2 in o2 mixture:
• The cylinder is first filled with co2 to an absolute pressure of 13.8 bar
• O2 then added to a total pressure of 138 bar
• The overall percentage of co2 is then 10%

28. Critical Temperature: this is the
temperature above which the gas cannot
be compressed to its liquid state with any
amount of pressure. So a gas can remain
in a liquid state below its critical
temperature
Critical Temp of N2O =
36.5˚C
Critical Temp of O2 = -119 ˚C
Critical Temp of co2 = 31˚C
Critical Temp of N2 = -147˚C

29.  When a mixture of gases is present such as the Entonox
mixture of 50% nitrous oxide and 50% oxygen
 There is a specific critical temperature at which the gas
mixture may separate out into its constituents
 Highest -5.5°C 117 bar
 Cylinder -7°C 137 bar
 Pipeline -30°C 4 bar

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