09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-1

Chapter 2The Structure of Thermodynamics

Notes on

Thermodynamics in Materials Science

by

Robert T. DeHoff

(McGraw-Hill, 1993).

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-2

Thermodynamic Systems

System --- That portion (subset) of the universe that is under study.

Surroundings --- Everything else. Usually, only the interaction with the immediate surroundings is relevant.

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-3

Classification of SystemsUnary versus Multicomponent --- How many

unique chemical species?Homogeneous versus Heterogeneous --- How many

unique phases?Closed versus Open --- Is matter exchanged with the

surroundings?Non-reacting versus Reacting --- Can chemical

reactions occur?Otherwise Simple versus Complex --- Are only

chemical, thermal, or mechanical effects involved? Are fields, surfaces, or elastic effects involved?

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-4

2.1 Classify the following thermodynamic systems:

• A solid bar of copper– Unary Multicomponent– Homogeneous Heterogeneous– Closed Open– Non-reacting Reacting– Otherwise simple Complex

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-5

2.1 Classify the following thermodynamic systems:

• A glass of ice water– Unary Multicomponent– Homogeneous Heterogeneous– Closed Open– Non-reacting Reacting– Otherwise simple Complex

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-6

2.1 Classify the following thermodynamic systems:

• An yttria stabilized zirconia furnace tube.– Unary Multicomponent– Homogeneous Heterogeneous– Closed Open– Non-reacting Reacting– Otherwise simple Complex

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-7

2.1 Classify the following thermodynamic systems:

• A styrofoam coffee cup

(just the polymer)– Unary Multicomponent– Homogeneous Heterogeneous– Closed Open– Non-reacting Reacting– Otherwise simple Complex

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-8

2.1 Classify the following thermodynamic systems:

• A styrofoam coffee cup

(the polymer and enclosed gas)– Unary Multicomponent– Homogeneous Heterogeneous– Closed Open– Non-reacting Reacting– Otherwise simple Complex

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-9

2.1 Classify the following thermodynamic systems:

• A eutectic alloy turbine blade rotating at 20,000 rpm:– Unary Multicomponent– Homogeneous Heterogeneous– Closed Open– Non-reacting Reacting– Otherwise simple Complex

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-10

Thermodynamic Properties

State Variables --- Values are determined by current condition & are independent of path.

Process Variables --- Have meaning only for changing systems.

Intensive Properties --- Have a value at each point in a system. May vary from point to point. Do not depend on the amount of matter.

Extensive Properties --- Values apply to the whole system. Depend on the amount of matter.

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-11

2.2 Without state functions thermodynamics would be useless. Discuss this assertion.

If there no state functions (like T, P, V, composition) then the behavior of all aspects of matter would depend explicitly on the history of the system.

There would be no variables that, by themselves, explicitly describe the current condition of any system.

Even the history experienced by the system could not be described in terms of some sequence of its properties.

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2.4 Why is heat a process variable?

Heat is fundamentally a flow of energy. Heat is transferred between two systems, or between parts of the same system.

The rearrangement of the distribution of energy is accompanied by changes in at least some of the properties of the system.

Such a change is a process

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-13

Thermodynamic Properties

State Variables --- Values are determined by current condition & are independent of path.

Process Variables --- Have meaning only for changing systems.

Intensive Properties --- Have a value at each point in a system. May vary from point to point. Do not depend on the amount of matter.

Extensive Properties --- Values apply to the whole system. Depend on the amount of matter.

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-14

• The mass density.– M/L3

– Kg/m3

2.3 Determine which of the following properties of a thermodynamic system are extensive/intensive:

Intensive Extensive

Intensive

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2.3 Determine which of the following properties of a thermodynamic system are extensive/intensive:

Intensive Extensive

Intensive

• The molar density.– M/L3

– Moles/m3

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2.3 Determine which of the following properties of a thermodynamic system are extensive/intensive:

Intensive Extensive

Extensive

• The number of gram atoms of alumina in a chunk of alumina.– M– Moles

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2.3 Determine which of the following properties of a thermodynamic system are extensive/intensive:

Intensive Extensive

Extensive

• The potential energy of the system in a gravitational field.– ML2/t2

– J

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2.3 Determine which of the following properties of a thermodynamic system are extensive/intensive:

Intensive Extensive

Intensive

• The molar concentration of NaCl in a salt solution.– M/L3

– Moles/m3

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2.3 Determine which of the following properties of a thermodynamic system are extensive/intensive:

Intensive Extensive

Extensive

• The heat absorbed by a gas in a cylinder when it is compressed.– M L2/t2

– J

09/19/2001 Notes from R.T. DeHoff, Thermodynamics in Materials Science (McGraw-Hill, 1993)2-20

Thermodynamic RelationsLaws --- 0th, 1st, 2nd, 3rd

Definitions --- Energy, …, Compressibility, ...

Coefficient Relations --- Z = Z(w,x,y,…)

Maxwell Relations ---

Criteria for Equilibrium --- S = maximum

Conditions for Equilibrium --- T = T

,...,,..., yxyw w

N

x

M

,...,ywx

ZN

,...,yxw

ZM