Enthalpy change of a system represents the heat added at___________________?
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Answer: A. constant pressure
Explanation
Enthalpy is defined mathematically as internal energy plus the product of pressure and volume. Differentiating this definition for a constant pressure process shows that enthalpy change equals added heat. This direct equivalence makes enthalpy an essential property for analyzing constant pressure heating systems. Constant pressure heating in open or closed systems allows boundary work to be accounted for automatically. Specific heat at constant pressure multiplies temperature change to yield enthalpy changes for ideal gases. Steam tables tabulate enthalpy values to simplify boiler and condenser energy balance calculations.
Boilers and heat exchangers operating at constant pressure use enthalpy to determine required heat transfer rates. Air conditioning and psychrometric chart calculations rely heavily on enthalpy to evaluate moist air heating. Chemical reactor design often assumes constant pressure conditions to simplify heat duty calculations. Constant temperature processes involve internal energy changes for ideal gases rather than direct enthalpy equivalence. Constant volume heat addition equals internal energy change, not enthalpy change. Constant entropy processes are adiabatic and reversible, involving zero heat addition altogether.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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