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Week 9: Lectures 25 – 27
Lecture 25: W 10/19
Lecture 26: F 10/21
Lecture 27: M 10/24
Reading:
BLB Ch 18.1 – 18.4, 5.5, 11.3 – 11.6
Homework:
BLB 18: 9, 11, 15, 29, 69; Supp 18: 1 – 3;
BLB 11:33, 37, 39, 31, 43, 47, 50; Supp 11:5  13
Reminder:
•
Angel Quiz 8 due on Thur 10/20
•
ALEKS Objective 9 due on Tue 10/25
•
Jensen Office Hour: 501 Chemistry Building
Tuesdays & Thursdays, 10:30 – 11:30 am
•
TA office hours, evening tutor sessions,
guided study group info posted on Angel >
Help Available
•
Exam 3: Monday Nov 7 6:30 – 7:45 pm
Jensen
Chem 110 Chap 10
Page: 2
Real gases deviate from ideal behavior
The 5 key postulates of KMT
!
Straightline motion in random directions
!
Molecules are small & have “no” volume
compared to the total volume
!
No intermolecular forces
!
Elastic collisions
!
Mean kinetic energy
!
"
T (in K)
For a nonideal gas (real gas) this is not true for two
types of conditions:
high P
low T
Reasons:
•
Molecules (or atoms) have a finite size
molecules occupy space
•
Molecules have attractive forces
these forces become stronger when they are
close together
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View Full Document Jensen
Chem 110 Chap 10
Page: 3
Real Gases – Pressure
For 1 mol of any ideal gas: PV/(RT) = 1
For 1 mol of different gases at same T & different P:
At low P, the idealgas equation is valid:
PV/(RT) = 1
In general, deviation from ideal behavior increases
as P increases:
•
At high P,
attractive forces between molecules
lead to the
appearance of a smaller n
PV/(RT) < 1
Example: CO
2
at 200 atm
•
At very high P,
finite molecular volume
leads to
repulsion
and the
appearance of a larger n
PV/(RT) > 1
Example: CO
2
at 800 atm
Low P
PV/(RT) ~ 1
High P: PV/(RT) < 1
Very high P
PV/(RT) > 1
Jensen
Chem 110 Chap 10
Page: 4
Real Gases – Temperature
For 1 mol of any ideal gas:
PV/(RT) = 1
For 1 mol of N
2
gas at different T & different P
•
At low T
, molecules stick together:
PV/(RT)
!
1
•
As temperature increases,
molecules move
faster,
the behavior of real gases becomes
more ideal.
Chem 110 Chap 10
Page: 5
Summary
Example:
Under which conditions is Ar(g) most
likely to approach ideal behavior?
A.
10 atm and 100°C
B.
1.0 atm and 200°C
C.
0.10 atm and –100°C
D.
20.0 atm and 100°C
E.
0.10 atm and 200°C
High P
PV/RT < 1
Attractive forces
lead to the
appearance of a
smaller
n
Very high P
PV/RT > 1
Finite molecular volume
leads to
repulsion
and the
appearance of a
larger
n
Low P
PV/RT
!
1
Attractive forces and
finite molecular volume
have
minimal
impact
As T
#
, real
gas behavior
becomes
more ideal
At high T,
Kinetic
energy
overcomes
attractive forces
Jensen
Chem 110 Chap 10
Page: 6
Correcting the Ideal Gas Law
•
For any gas, we can measure P, V, T
•
At higher P
,
measured P is too small
due to attractive forces between
molecules
The amount of “missing” P is
proportional to
1. size of attractive forces (
a
):
2. frequency of collisions: (
n
2
/V
2
)
To compensate
, use:
•
At higher P, measured V is too
large
due to finite molecular
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This note was uploaded on 01/18/2012 for the course CHEM 110 taught by Professor Hofmann,brucerob during the Fall '08 term at Pennsylvania State University, University Park.
 Fall '08
 HOFMANN,BRUCEROB
 Mole

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