Internal energy vs. Enthelpy vs. Entropy

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SUMMARY

The discussion clarifies the distinction between two thermodynamic equations: Q=m(u2-u1) + W and Q=m(h2-h1). The first equation is universally applicable in closed systems, while the second equation is specifically valid under constant pressure conditions. Users should apply the first equation for general energy calculations and the second when dealing with processes at constant pressure, particularly when volume changes occur. Understanding these contexts ensures accurate application of thermodynamic principles.

PREREQUISITES
  • Basic understanding of thermodynamics
  • Familiarity with the concepts of internal energy and enthalpy
  • Knowledge of closed systems in thermodynamic processes
  • Understanding of work (W) in thermodynamic equations
NEXT STEPS
  • Study the principles of thermodynamics, focusing on internal energy and enthalpy
  • Learn about the First Law of Thermodynamics and its applications
  • Explore constant pressure processes and their implications in thermodynamics
  • Investigate real-world applications of these equations in engineering contexts
USEFUL FOR

Students and professionals in engineering, particularly those studying thermodynamics, as well as anyone involved in energy calculations in closed systems.

ipocoyo
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What is the difference between Q=m(u2-u1) + W & Q=m(h2-h1)?

Basically I am trying to figure out 2 different sets of questions and apparently using these separate equations yield different answers, and I don't know which equation to use. From my understanding, both of them are used in closed systems and also when there is a constant pressure but a change in volume? So when exactly do I use which one?
 
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ipocoyo said:
What is the difference between Q=m(u2-u1) + W & Q=m(h2-h1)?

Basically I am trying to figure out 2 different sets of questions and apparently using these separate equations yield different answers, and I don't know which equation to use. From my understanding, both of them are used in closed systems and also when there is a constant pressure but a change in volume? So when exactly do I use which one?
The first equation is always true. The second equation applies when the pressure is constant during the process, and equal to the initial pressure of the gas.
 

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