Internal energy vs. Enthelpy vs. Entropy

This means that the volume will change, but the pressure will stay the same. The first equation can be used in any situation, but the second equation is only applicable in specific circumstances. In summary, the main difference between Q=m(u2-u1) + W and Q=m(h2-h1) is that the latter can only be used when there is a constant pressure and a change in volume, while the former can be used in any situation.
  • #1
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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  • #2
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.
 

1. What is the difference between internal energy and enthalpy?

Internal energy is the total energy stored within a system, including both kinetic and potential energy. Enthalpy, on the other hand, is the total energy of a system plus the energy required to create or destroy the system's volume. In simpler terms, internal energy is the energy contained within a system, while enthalpy is the energy required to create or destroy that system.

2. How are internal energy and enthalpy related to each other?

Internal energy and enthalpy are related through the equation H = U + PV, where H is enthalpy, U is internal energy, P is pressure, and V is volume. This equation shows that enthalpy is equal to the internal energy plus the energy required to create or destroy the system's volume.

3. What is entropy and how does it differ from internal energy and enthalpy?

Entropy is a measure of the disorder or randomness within a system. Unlike internal energy and enthalpy, which are measures of the total energy within a system, entropy is a measure of the energy dispersal or distribution within a system. It is a property that increases over time in closed systems and is related to the heat flow within a system.

4. How do changes in temperature affect internal energy, enthalpy, and entropy?

As temperature increases, so does the internal energy of a system. This is because at higher temperatures, molecules have more kinetic energy, leading to an increase in the system's total energy. Enthalpy also increases with temperature, as the energy required to create or destroy the system's volume also increases. Entropy, on the other hand, can either increase or decrease with temperature, depending on the system and the processes taking place.

5. How are internal energy, enthalpy, and entropy used in thermodynamics?

Internal energy, enthalpy, and entropy are all important concepts in thermodynamics, the study of energy and its transformations. These properties are used to understand and predict the behavior of physical systems, particularly in relation to energy transfer, phase transitions, and chemical reactions. They also play a crucial role in determining the efficiency and feasibility of various energy processes and systems.

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