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Defining Maxwell’s Equations. The fundamental equations can be expressed as: from which the following relationships are derived:. Maxwell’s Equations. The fundamental property relations are exact differentials , meaning that for: defined as: 6.11 then we have,
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Defining Maxwell’s Equations • The fundamental equations can be expressed as: • from which the following relationships are derived: Lecture 5
Maxwell’s Equations • The fundamental property relations are exact differentials, meaning that for: • defined as: • 6.11 • then we have, • 6.12 • When applied to equations 6.7-6.10 for molar properties, we derive Maxwell’s relations: • 6.13-6.16 Lecture 5
Maxwell’s Equations - Example #1 • We can immediately apply Maxwell’s relations to derive quantities that we require in later lectures. These are the influence of T and P on enthalpy and entropy. • Enthalpy Dependence on T,P-closed system • Given that H=H(T,P): • The final expression, including the pressure dependence is: • 6.20 • Which for an ideal gas reduces to: • 6.23 Lecture 5
Maxwell’s Equations - Example #2 • Entropy Dependence on T,P-closed system • Given that S=S(T,P) • The final expression, including the pressure dependence is: • 6.21 • Which for an ideal gas reduces to: • 6.24 Lecture 5
Example SVNA 6.21 - The state of 1(lbm) of steam is changed from saturated vapour at 20 psia to superheated vapour at 50 psia and 1000F. What are the enthalpy and entropy changes of the steam? What would the enthalpy and entropy changes be if steam were an ideal gas? Properties from Steam Tables (SVNA): Lecture 5