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.
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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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Derive the thermodynamic identity for (equation 5.23), and from it the three partial derivative relations 5.24.
Calcium carbonate, CaCO3, has two common crystalline forms, calcite and aragonite. Thermodynamic data for these phases can be found at the back of this book.
(a) Which is stable at earth's surface, calcite or aragonite?
(b) Calculate the pressure (still at room temperature) at which the other phase
should become stable.
Problem 5.35. The Clausius-Clapeyron relation 5.47 is a differential equation that can, in principle, be solved to find the shape of the entire phase-boundary curve. To solve it, however, you have to know how both L and V depend on temperature and pressure. Often, over a reasonably small section of the curve, you can take L to be constant. Moreover, if one of the phases is a gas, you can usually neglect the volume of the condensed phase and just take V to be the volume of the gas, expressed in terms of temperature and pressure using the ideal gas law. Making all these assumptions, solve the differential equation explicitly to obtain the following formula for the phase boundary curve:
P= (constant) x e-L/RT
This result is called the vapour pressure equation. Caution: Be sure to use this formula only when all the assumptions just listed are valid.
In this problem you will investigate the behavior of a van der Waals fluid near the critical point. It is easiest to work in terms of reduced variables throughout.
(a) Expand the van der Waals equation in a Taylor series in , keeping terms through order . Argue that, for T sufficiently close to Tc, the term quadratic in becomes negligible compared to the others and may be dropped.
(b) The resulting expression for P(V) is antisymmetric about the point V = Ve. Use this fact to find an approximate formula for the vapor pressure as a function of temperature. (You may find it helpful to plot the isotherm.) Evaluate the slope of the phase boundary,
( c) Still working in the same limit, find an expression for the difference in volume between the gas and liquid phases at the vapor pressure. You should find .8, where (3 is known as a critical exponent. Experiments show that (3 has a universal value of about 1/3, but the van der Waals model predicts a larger value.
(d) Use the previous result to calculate the predicted latent heat of the transformation as a function of temperature, and sketch this function.
The shape of the T = Tc isotherm defines another critical exponent, called Calculate 5 in the van der Waals model. (Experimental values of 5 are typically around 4 or 5.)
A third critical exponent describes the temperature dependence of the isothermal compressibility, K=-t This quantity diverges at the critical point, in proportion to a power of (T-Tc) that in principle could differ depending on whether one approaches the critical point from above or below. Therefore the critical exponents 'Y and -y' are defined by the relations
Calculate K on both sides of the critical point in the van der Waals model, and show that 'Y = -y' in this model.
Plumber's solder is composed of 67% lead and 33% tin by weight. Describe what happens to this mixture as it cools, and explain why this composition might be more suitable than the eutectic composition for joining pipes.
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