Lecture 4 Highlights…
Æ Avogadro’s Law
ÆIdeal Gas Law
• PV = nRT
ÆWork some problems…..
ÆGas Density
Constant Temperature and
Pressure
V ∝ n at constant T. Avogadro’s Law !
Ideal Gas Equation
PV = nRT
Where:
•R = “Gas Constant”
•T in degrees Kelvin
R depends on units used for P and V
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Ideal Gas Equation
PV = nRT
Values for the Gas
Constant (R)
Units
L . atm/(mol . K)
Kg . m2/s2 . (mol . K)
J/(mol . K)
m3 . Pa/(mol . K)
L . torr/(mol . K)
Value of R
0.08206
8.314
8.314
8.314
62.36
Handy Reference Point: Standard
Temperature and Pressure (STP)
) 0°C, 273 degrees Kelvin
) 1 atm Pressure
) Solving for PV=nRT, the volume associated
with 1 mole of gas is 22.4 liters (L) at STP
) This value is known as the Molar Volume of an
ideal gas (22.4 L/mol)
) This is the same for all ideal gases !!
) Gas density is then:
• Molar Mass (g/mol) / Molar Volume (L/mol) = Density (g/L)
More Words on Gas Density…
P
n
=
RT V
MP nM
=
=d
RT
V
; Multiply both sides by M = Molar Mass
; (mol x g/mol)/(liters) = density (g/L)
Or…
d =
MP
RT
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Why Do “Hot Air” Balloons Work ?
Intermolecular Forces (IMFs) at
Work in Real Gases…
In this case, IMF’s cause lower hit frequency
and less force when molecules hit the wall !!
Different Behavior of
Different “Real Gases”
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