c04 JWBS043-Rogers September 13, 2010 11:24 Printer Name: Yet to Come
PROBLEMS AND EXAMPLE 69Problem 4.3
The enthalpy of formation of liquid acetic acid CH 3 COOH(l) is fH◦=
− 484 .5kJmol−^1. What iscH?Problem 4.4
The enthalpy of combustion of solidα-d-glucose, C 6 H 12 O 6 (s) is−2808 kJ mol−^1.
What is its enthalpy of formation?Problem 4.5
EstimatecH^298 (n-octane(g)) ofn-octane by the hydrogen-atom counting method
for alkanes.Problem 4.6
FindfH^298 (2,4-dimethylpentane(g)) by the hydrogen atom counting method. What
is the enthalpy of isomerization ofn-heptane(g) to 2,4-dimethylpentane(g) according
to this method? Compare your answer with the experimental result of−14.6±
1.7 kJ mol−^1.Problem 4.7
The input file for a Gaussian©Cquantum mechanical calculation will be discussed
in later chapters. Briefly, it consists of a few lines of instructions to the computer
concerning memory requirements, the number of processors to be used, and the
Gaussian procedure to be used, followed by an approximate geometry of the molecule.
In simple cases, the input geometry can be merely a guess based on what we learned
in general chemistry. The machine specifications will vary from one installation to
another. Our input file for the water molecule is%mem=1800Mw
%nproc= 1#g3water01
H -1.012237 0.210253 0.097259
O -0.260862 0.786229 0.119544
H 0.489699 0.209212 0.142294Adapt this input file for your system and run the water molecule. What is the optimized
geometry in the form of Cartesian coordinates (like the input file)? What is the O H
bond length? What is the H O H bond angle? What energy is given for water?