Chapter 3 The First Law

1
Chapter 3 The First Law

• The Machinery

2
Constant V

• Recall,

term for the internal pressure

• If V is constant,

3
The Change in Internal Energy at Constant Volume
4
Internal Pressure
5
An Ideal Gas

• In an ideal gas, there is no interaction between
  molecules, so U is independent of V.

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What Happens at Constant P?

• In an ideal gas, there is no interaction between
  molecules, so U is independent of V.

• If P is constant, then

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The Expansion Coefficient

• The Definition

• Substitute a in constant P equation

• Note that the magnitude of a is proportional to
  the response of the volume to a change in T.

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Self-Test 3.2, p. 79

• The Definition

9
Joule-Thompson Coefficient and Isothermal
Compressibility

• Recall, enthalpy?

• Also, recall that DH/DTCP

• Also, recall that DHqP

• Lets do the same thing for H as we did for U in
  expressing simultaneous changes in P and T

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Joule-Thompson Coefficient and Isothermal
Compressibility
CP
11
Joule-Thompson Coefficient and Isothermal
Compressibility

• Presto-Chango

• This equation now gives us two important
  definitions
• Isothermal compressibility, kT
• Joule-Thompson coefficient, m

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Joule-Thompson Coefficient and Isothermal
Compressibility