Page 17 - Physical Chemistry

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Preface • Section 2.12 contains advice on how to solve problems in physical chemistry.

2.12 PROBLEM SOLVING
Trying to learn physical chemistry solely by reading a textbook without working prob-
lems is about as effective as trying to improve your physique by reading a book on
body conditioning without doing the recommended physical exercises.
If you don’t see how to work a problem, it often helps to carry out these steps:
1. List all the relevant information that is given.
2. List the quantities to be calculated.
3. Ask yourself what equations, laws, or theorems connect what is known to what is
unknown.
4. Apply the relevant equations to calculate what is unknown from what is given.

• The derivations are given in full detail, so that students can readily follow them.
The assumptions and approximations made are clearly stated, so that students will
be aware of when the results apply and when they do not apply.
• Many student errors in thermodynamics result from the use of equations in situa-
tions where they do not apply. To help prevent this, important thermodynamic
equations have their conditions of applicability listed alongside the equations.
• Systematic listings of procedures to calculate q, w, ¢U , ¢H, and ¢S (Secs. 2.9
and 3.4) for common kinds of processes are given.
• Detailed procedures are given for the use of a spreadsheet to solve such problems
as fitting data to a polynomial (Sec. 5.6), solving simultaneous equilibria
(Sec. 6.5), doing linear and nonlinear least-squares fits of data (Sec. 7.3), using an
equation of state to calculate vapor pressures and molar volumes of liquids and
vapor in equilibrium (Sec. 8.5), and computing a liquid–liquid phase diagram by
minimization of G (Sec. 12.11).

154
Chapter 5 A B C D E F
Standard Thermodynamic
Functions of Reaction 1 CO Cp polynomial fit a b c d
2 T/K Cp Cpfit 28.74 -0.00179 1.05E-05 -4.29E-09
Figure 5.7 3 298.15 29.143 29.022
4 400 29.342 29.422
3
2
Cubic polynomial fit to C° P,m of 5 500 29.794 29.923 y = -4.2883E-09x + 1.0462E-05x -
CO(g). CO C P, m 1.7917E-03x + 2.8740E+01
6 600 30.443 30.504
7 700 31.171 31.14 36
8 800 31.899 31.805
34
9 900 32.577 32.474
10 1000 33.183 33.12 32
11 1100 33.71 33.718 30
12 1200 34.175 34.242
13 1300 34.572 34.667 28
14 1400 34.92 34.967 0 500 1000 1500
15 1500 35.217 35.115
• Although the treatment is an in-depth one, the mathematics has been kept at a rea-
sonable level and advanced mathematics unfamiliar to students is avoided.
• The presentation of quantum chemistry steers a middle course between an exces-
sively mathematical treatment that would obscure the physical ideas for most un-
dergraduates and a purely qualitative treatment that does little beyond repeat what
students have learned in previous courses. Modern ab initio, density functional,
semiempirical, and molecular mechanics methods are discussed, so that students
can appreciate the value of such calculations to nontheoretical chemists.