University College - Chemistry Chem 112A Lecture Notes - Lecture 38: Partial Pressure, Glossary Of Ancient Roman Religion
13 Dec 2016
School
Department
Professor
22 April 2016
Lecture 38: Raoult’s Law
Equation of the Day: Ptotal =
+
I. Raoult’s Law
A. Basics
1. If we have two liquids A and B in a container:
a. The pure vapor pressure of pure A =
b. The mole fraction of A in the liquid =
c. PA in the container =
d. PB in the container =
2. The total pressure = PA + PB
a. Raoult’s Law: Ptotal =
+
3. Example: 50 g H2O and 50 g ETOH at 298K
a. Using molar masses, we get 1.085 mol ETOH and 2.775 mol H20
b.
(1.085)/(1.085 + 2.775) = 0.281
c.
0.719
d.
= 0.0780 atm
• We get ∆G0vap from ∆Gf(gas) - ∆Gf(liquid)
e.
= 0.0312 atm
f. Ptot =
+
= 0.0443 atm
B. Applying Dalton’s Law
1. For a mixture of gases, A and B, exerting a total pressure of Ptotal, the partial pressure due to a
(PA) is the
and the partial pressure due to B (PB) is
a. From this, we can get the
=PA/Ptotal = 0.494 and
=PB/Ptotal = 0.506
b. Notice, that due to vapor pressure, ethanol is enriched in the vapor phase
2. Plotting Vapor Pressure vs.
a. For
for this example
b. The
(where
is the slope)
c. The
d. The Ptotal = (
C. Non-Ideal Behavior
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