hale. Assuming ideal gas behavior, what’s the change in en-
tropy of the air? Assume a temperature of 37°C.
3.44.Set up expressions to calculate the work and heat for
the four steps of a Carnot cycle. Define initial conditions for
pressure and volume of a given amount (say, 1 mole) of an
ideal gas, and calculate wand qfor each step in the cycle and
the total work and heat of the cycle. Show that S0 for
the cycle if it is done reversibly. You may have to specify other
variables.
3.45.Numerically determine Sfor the isobaric change
in temperature of 4.55 g of gallium metal as it is heated
from 298 K to 600 K if its molar heat capacity is given by
the expression Cp27.49 2.226 10 ^3 T1.361
105 /T^2. Assume standard units on the expression for heat
capacity.
3.46.Plots of Cp/Tversus Tare used to determine the entropy
of a material, as the entropy value would be the area under
the curve. For sodium sulfate, Na 2 SO 4 , the following data are
available:
T(K) Cp(cal/K)
13.74 0.171
16.25 0.286
20.43 0.626
27.73 1.615
41.11 4.346
52.72 7.032
68.15 10.48
82.96 13.28
95.71 15.33
Source: G. N. Lewis and M.
Randall,Thermodynamics,rev.
K. Pitzer and L. Brewer, McGraw-
Hill, New York, 1961
Extrapolate to 0 K using a function f(T) kT^3 , where kis some
constant. Using your plot, numerically evaluate the experi-
mental entropy of Na 2 SO 4 at 90 K.88 Exercises for Chapter 3
Symbolic Math Exercises