Chapter 8 and 9 – Energy Balances

CBE2124, Levicky 1 Chapter 8 and 9 Energy Balances Reference States. Recall that enthalpy and internal Energy are always defined relative to a reference state ( Chapter 7). When solving Energy balance problems, it is therefore necessary to define a reference state for each chemical species in the Energy balance (the reference state may be predefined if a tabulated set of data is used such as the steam tables). Example. Suppose water vapor at 300 oC and 5 bar is chosen as a reference state at which H is defined to be zero. Relative to this state, what is the specific enthalpy of liquid water at 75 oC and 1 bar? What is the specific internal Energy of liquid water at 75 oC and 1 bar? (Use Table B. 7). Calculating changes in enthalpy and internal Energy . H and U are state functions, meaning that their values only depend on the state of the system, and not on the path taken to arrive at that state. IMPORTANT: Given a state A (as characterized by a set of variables such as pressure, temperature, composition) and a state B, the change in enthalpy of the system as it passes from A to B can be calculated along any path that leads from A to B, whether or not the path is the one actually followed.

Chapter 8 and 9 – Energy Balances Reference States. Recall that enthalpy and internal energy are always defined relative to a reference state (Chapter 7). When solving energy balance problems, it is therefore necessary to define a reference state for each chemical species in the energy balance (the reference state may be predefined if a ...

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  Balance, Energy, Energy balance

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