Chapter 5: 5.21 (page 166)
Is heat capacity (C) extensive or intensive? What about specific heat (c) ? Explain briefly.
Short Answer
Heat capacity is an extensive property
Specific heat is an intensive property.
Chapter 5: 5.21 (page 166)
Is heat capacity (C) extensive or intensive? What about specific heat (c) ? Explain briefly.
Heat capacity is an extensive property
Specific heat is an intensive property.
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Get started for freeIn this problem you will derive approximate formulas for the shapes of the phase boundary curves in diagrams such as Figures 5.31 and 5.32, assuming that both phases behave as ideal mixtures. For definiteness, suppose that the phases are liquid and gas.
(a) Show that in an ideal mixture of A and B, the chemical potential of species A can be written where A is the chemical potential of pure A (at the same temperature and pressure) and . Derive a similar formula for the chemical potential of species B. Note that both formulas can be written for either the liquid phase or the gas phase.
(b) At any given temperature T, let x1 and xgbe the compositions of the liquid and gas phases that are in equilibrium with each other. By setting the appropriate chemical potentials equal to each other, show that x1and xg obey the equations = and where represents the change in G for the pure substance undergoing the phase change at temperature T.
(c) Over a limited range of temperatures, we can often assume that the main temperature dependence of comes from the explicit T; both are approximately constant. With this simplification, rewrite the results of part (b) entirely in terms of TA, and TB (eliminating ). Solve for x1and xgas functions of T.
(d) Plot your results for the nitrogen-oxygen system. The latent heats of the pure substances are. Compare to the experimental diagram, Figure 5.31.
(e) Show that you can account for the shape of Figure 5.32 with suitably chosen values. What are those values?
The formula for Cp-Cv derived in the previous problem can also be derived starting with the definitions of these quantities in terms of U and H. Do so. Most of the derivation is very similar, but at one point you need to use the relation .
Repeat the preceding problem with T/TC=0.8
Show that equation 5.40 is in agreement with the explicit formula for the chemical potential of a monatomic ideal gas derived in Section 3.5. Show how to calculate for a monatomic ideal gas.
Suppose that a hydrogen fuel cell, as described in the text, is to be operated at and atmospheric pressure. We wish to estimate the maximum electrical work done by the cell, using only the room temperature data at the back of this book. It is convenient to first establish a zero-point for each of the three substances, . Let us take for both to be zero at , so that G for a mole of is at .
(a) Using these conventions, estimate the Gibbs free energy of a mole of at . Repeat for .
(b) Using the results of part (a), calculate the maximum electrical work done by the cell at , for one mole of hydrogen fuel. Compare to the ideal performance of the cell at.
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