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03.5 Mixture Properties for Ideal Solutions
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- Chapter 1 - Basic concepts
- Chapter 2 - The energy balance
- Chapter 3 - Energy balances for composite systems.
- Chapter 4 - Entropy
- Chapter 5 - Thermodynamics of Processes
- Chapter 6 - Classical Thermodynamics - Generalization to any Fluid
- Chapter 7 - Engineering Equations of State for PVT Properties
- Chapter 8 - Departure functions
- Chapter 9 - Phase Equlibrium in a Pure Fluid
- Chapter 10 - Introduction to Multicomponent Systems
- Chapter 11 - An Introduction to Activity Models
- Chapter 12 - Van der Waals Activity Models
- Chapter 13 - Local Composition Activity Models
- Chapter 14 - Liquid-liquid and solid-liquid equilibria
- Chapter 16 - Advanced Phase Diagrams
- Chapter 15 - Phase Equilibria in Mixtures by an Equation of State
- Chapter 17 - Reaction Equilibria
- Chapter 18 - Electrolyte Solutions
Stream Enthalpy Using the "Heat of Formation" Pathway
Stream enthalpies for the DME process (uakron, 7min) can be estimated using the "heat of reaction" pathway (Fig 3.5a) or the "heat of formation" pathway (Fig 3.5b). This presentation is based on Fig 3.5b, which is very similar to Fig 2.6c. The main difference is the inclusion of the heat of formation for each compound relative to its elements. Including the heat of formation puts the reference state for each compound on the same basis of comparison (ie. the elements). If one stream (e.g. "products") possesses more enthalpy than another stream (e.g. "reactants") then the energy difference between the streams (e.g. "heat of reaction") would be accounted for by simply subtracting the two stream enthalpies. Reactions inherently involve multiple components, so including the heats of formation in the stream enthalpies, as well as the other enthalpic contributions represented in Fig 2.6c, is inevitable. These sample calculations are illustrated for all the streams appearing in the DME process. The presentation follows up on the discussion of Fig 2.6c for pure fluids. Once you understand the calculations for each pure fluid, the mixture property simply involves taking the molar average, so: H ≈ ∑(xi*Hfi+CpiigΔT+(qi-1)*Hivap). In this equation, (qi-1)*Hivap accounts crudely for departures from ideal gas behavior. For example, if a stream is a vapor, then q=1 and Hvap doesn't matter. If q=0, then the stream is a liquid and Hvap must be subtracted. We will study more accurate models of ideal gas departures in Unit II.
Comprehension Questions:
1. Compute the enthalpy, H(J/mol), of methanol at 250C and 2 bars relative to its ideal gas standard state elements.
2. Compute the enthalpy, H(J/mol), of DME at 250C and 2 bars relative to its ideal gas standard state elements.
3. Compute the enthalpy, H(J/mol), of water at 250C and 2 bars relative to its ideal gas standard state elements.
4. Compute the enthalpy, H(J/mol), of a stream that is 50% methanol, 25% DME, and 25% water at 250C and 2 bars relative to its ideal gas standard state elements.