PETE 310
Lecture # 9
Ideal Gases
Ideal Gas
Characterized by 3 state variables: P, T,
and V  relationship among these from
equations of state
Equations of State
The Ideal Gas
Ideal gas properties
Volume of gas molecules is negligible
compared with gas volume
Forces of attraction or repulsion between
molecules or walls of container are zero
No loss of internal energy due to collisions
Ideal Gas Laws from Experiments…
Boyle’s Law (at constant T)
1
V
P
Gay-Lussac’s ( or Charles ) law (at constant
P)
V T
Ideal Gas Laws
Avogadros’s Law  At the same P and T
equal volumes of gas contain the same #
of molecules
Avogadro’s Number:
Na = 2. 73X1026 molecules/lb mole
Internet Lesson on Ideal Gas Behavior
Experimental instructions
& Problems with solutions
Boyle
Can you Write this Law?
Boyles law
http://www.grc.nasa.gov/WWW/K12/airplane/aboyle.html (Public domain file)
Ideal Equation of State
Construction
Step 1
P1V1  P2V x
T2
T1
Step 2
x
P1
V V2

T1 T2
P2
Combining
P1V1 P2V2

T1
T2
V1
Vx
V2
Jacques Charles (1746-1823)
Never published his results
Joseph Gay-Lussac (1778-1850)
Describing Gas Behavior
Evolution of Science - From ideal gases to
real gases
Boyle & Charles laws
1

V  
P T

P1V1 P2V2

T1
T2
V  T P
PVM
R
T
(VM  V / n)
R = gas constant, depends upon units used
See page 95 McCain book
Ideal Gas Mixture
The pressure in a vessel containing an
ideal gas mixture (n) or a single gas
component (nk) is
nRT
P
Vt
nk RT
Pk 
Vt
http://home.a-city.de/walter.fendt/phe/gaslaw.htm
Partial Pressure
P
Pk nk

 yk
P
n
T
1
Pk is the partial pressure
of component k, and by
definition
Nc
P
i 1
k
n
,n ,
1
2
…, n
k
P
p
k
T
nk
1
Law of Partial Pressures John
Dalton (1766-1844)
Law of Partial
Pressures
Density of ideal gas
nRT
m
P
P


Vt
M wVt
RT
Watch out the units!
Mixtures of Ideal Gases
Dalton’s law of partial pressures
Amagat’s law of partial volumes
Specific gravity of a gas
Ideal Gas Laws & Exercises
Apparent Molecular Weight of a
Gas Mixture
Determine the Mwa and density of a
mixture of 30%C1, 40%C2, and 30%C3 at
T=200oF and P=4000 psia