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S.I. unitsGases and Gas Laws
ByAhmed Ibrahim ; M.D.
Prof.of AnesthesiaAin Shams University
Anesthesia DepartmentAnesthesia Department
©
IIntended LLearning OOutcomes
By the end of this lecture , the student will be able to:
1..know different units used for clinical measurements .2..understand different laws controlling ideal gas behavior.3..interpret the applications of different gas laws in anesthetic practice.
Meter m length
Kilogram Kg mass
Second s time
Ampere A electric current
Kelvin oK temperature
Mole mol amount of substance
Candela cd luminous intensity
Basic 7 S.I units
Fractions & Multiples
10-18, 10-15, 10-12, 10-9, 10-6, 10-3, 10-2, 10-1 10 102 103 106 109 1012 1015 1018
atto femto pico nano micro milli centi deci deca hecto kilo mega giga tera penta exa
a f p n µ m c d Da h K M G T P E
•area m2
•volume m3
•velocity displacement / time ms-1
•acceleration velocity / time ms-2
•force mass x acceleration Kgms-2 Newton N •work (energy) force x distance Kgm2s-2, Nm Joule J•power work / time Kgm2s-3, Js-1 Watt W •pressure force / area Nm-2 Pascal Pa
•frequency cycles / second Hertz Hz
•electric charge electric current x time Coulomb C
•potential difference (EMF)
Volt V
•electric resistance potential difference / current Ohm Ω
•electric capacitance Farad F
•magnetic flux Weber Wb
SOLID LIQUID GAS/VAPOUR
I.M.FORCE +++ ++ +I.M.SPACE + ++ +++MOLECULAR MOTION ± ++ +++SHAPE OF CONTAINER NO YES YES
MISSIBILITY NO YES YES
VAPOUR gaseous state of the substance which is present in the liquid form at RTP
GAS a substance which cannot exist in the liquid form at RTP
Kinetic Theory of Gases
GAS MOLECULES are:
•Widely separated (negligible molecular volume)
•In constant motion (diffusion)
•In constant striking (pressure)
IDEAL (PERFECT) GAS, obeys the 3 assumptions
TEMP PRESSURE
VOLUME
GAS
Robert Boyle (1627-1691). , Ireland
Jacques Charles (1746-1823)
Critical Temperature “ the temperature above which a gas cannot be liquefied whatever pressure is applied ”
Critical Pressure ” the pressure needed to liquefy a gas at its critical temperature “
N.B. in T in P needed
CO2 31oCN2O 36.5 oC (C.P = 74 atm)O2 -116oC
for a given mass of a gas, at a constant:
TEMPERATURE PRESSURE VOLUME
V 1/P
P x V =Const.
P1xV1= P2xV2
V T(oA)
V=T x Const. (K)
V/T = K
P T
Boyle’s law Charles' law Gay-Lussac’s law
a Perfect Gas ,is the one that always obey Boyle’s and Charles’ laws. in which the intermolecular forces and molecular volume are too small ( negligible ).
a Real Gas behaves approximately as a perfect gas especially at low pressures and high temperatures.
Equation of state of a perfect gas:
V 1/P V T
V T/P
V = T/P x const
PV/T = const (R)
P1V1 / T1 = P2V2 / T2
Avogadro’s hypothesis
Volumes
for perfect gases at EQUAL Temp contain equal number of molecules
Pressure
1 mole of any gas at , STP 22.4 L Room temp 24.1 L
Body temp 25.4 L
NB. a mole of volatile liquid (e.g. 197.4 gm Halothane) 22.4 L vapour at STP
PV=RT
R (molar gas constant) = 1 x 22.4 / 273=0.082 litre.atm /degree oA/ mole =1.987 joule / degree / mole (S.I)
A mole of any gas contains the same number of molecules = 6.02 x 1023………… ……………….” Avogadro’s number”
Amadeo Avogadro (1776-1856) Italy
John Dalton 1766-1844
DALTON’S law of Partial Pressure
“ the pressure exerted by a mixture of gases (and/ or vapours) – enclosed in a given space – is equal to the sum of pressures which each gas (or vapour) would exert if it alone occupied the same space”
Partial Pressure (P.P) = total pressure x volume %Volume % = (P.P / total P ) x 100
Saturated Vapor Pressure (SVP) varies as a function of:
•nature of liquid •its temperature
mmHg (20oC)
-Desflurane 670
-Diethyl ether 440
-Halothane 243
-Isoflurane 239
-Enflurane 175
-Sevoflurane 160
-Trilene 60
-Methoxyflurane 23
Summary of important pointsSummary of important points•Basic S.I units
- length = Meter m- mass = Kilogram Kg- time = Second s- electric current = Ampere A- temperature = Kelvin oK- amount of substance = Mole mol- luminous intensity = Candela cd
•Derived units- area = m2
- volume = m3
- velocity =ms-1
- acceleration = ms-2
- force =Kgms-2 = Newton N - work (energy) = Kgm2s-2 = Nm = Joule J- power = Kgm2s-3 = Js-1 = Watt W
- pressure = Nm-2 = Pascal Pa- frequency = Hertz Hz- electric charge = Coulomb C- potential difference (EMF) =Volt V- electric resistance = Ohm Ω- electric capacitance = Farad F- magnetic flux = Weber Wb
•VAPOUR is the gaseous state of the substance which is present in the liquid form at RTP
•GAS is a substance which cannot exist in the liquid form at RTP
•Boyle’s law : V 1/P at constant temperature
•Charles' law : V T (oA) at constant pressure
•Gay-Lussac’s law : P T at constant volume
•Critical Temperature : “ the temperature above which a gas cannot be liquefied whatever pressure is applied ”
•Avogadro’s hypothesis : “EQUAL volumes of perfect gases at same temperature and pressure contain same number of molecules”
•Avogadro’s number : A mole of any gas contains the same number of molecules = 6.02 x 1023
•DALTON’S law of Partial Pressure Partial Pressure (P.P) = total pressure x volume %
Examples of questions to assess the ILOsExamples of questions to assess the ILOs
1. Which of the following units are BASIC SI units of measurement?
a) Kilometre.
b) Candela.
c) Watt.
d) Kilogram.
2.The following are correct S.I. Units
a) The unit of energy is the Newton
b) The unit of power is the Watt
c) The unit of frequency is the Hertz
d) The unit of mass is the gram
a) The unit of length is the metre
3.The critical temperature is:
a) 273 K
b) the temperature above which a gas cannot be liquified by pressure alone
c) the temperature below which a gas does not vaporise
d) 36.5 degrees C for nitrous oxide
e) different if a substance is in a mixture rather than on its own
4.Concerning the gas laws
a) Boyle's law refers to the relationship between temperature and pressure of a gas
b) Temperature is measured on the absolute temperature scale
c) Temperature is a constant in Charles' law
d) Boyle's law states that at a constant volume pressure varies with temperature
e) The gas laws are only true for air
5.One mole of a gas
a) Occupies 22.4 Litres at room temperature
b) Has the same volume for any gas
c) Contains Avogadro's number of molecules
d) May be liquefied by compression if above critical temperature
e) Is one gram molecular weight
Answers
1. false, true, false, true
2. false, true ,true, false, true
3. false, true, false, true, true
4. false, true, false, false, false
5. false, true, true, false, true
Thank You
