Why can U be expanded in terms of T and V?

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In summary, when expressing dS as a function of dV and dT, dU was expanded out as shown in the screenshot. It is possible to expand dU in this way due to a mathematical rule. However, this expansion does not change the meaning of the expression. It is also worth noting that a single phase material of constant composition can be specified by two intensive properties.
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thegirl
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when expressing dS as a function of dV and dT, dU was expanded out as you can see in the screenshot below, is there a mathematical rule which allows this? does the fact that the internal energy is expanded out change the meaning of the expression?
Screen Shot 2016-03-24 at 17.45.17.png
 
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How many intensive properties are required to specify the state of a single phase material of constant composition?
 
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thegirl said:
when expressing dS as a function of dV and dT, dU was expanded out as you can see in the screenshot below, is there a mathematical rule which allows this? does the fact that the internal energy is expanded out change the meaning of the expression?View attachment 97881
dU/dT(V)+dU/dV(T) is the differential of U with the coordinated (T,V)
 
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Thank you!
 

1. Why is it important to expand U in terms of T and V?

It is important to expand U (internal energy) in terms of T (temperature) and V (volume) because it allows us to better understand the relationship between these variables and how they affect the system. This expansion also helps us to analyze and predict the behavior of the system under different conditions.

2. How is U expanded in terms of T and V?

U can be expanded in terms of T and V using the first law of thermodynamics, which states that the change in internal energy (ΔU) is equal to the heat (Q) added to the system minus the work (W) done by the system. This can be expressed as ΔU = Q - W. By rearranging this equation and substituting for Q and W in terms of T and V, we can expand U as a function of these variables.

3. What are the advantages of expanding U in terms of T and V?

Expanding U in terms of T and V allows us to study the thermodynamic properties of a system in a more comprehensive and systematic manner. It also helps us to simplify complex systems and make predictions about their behavior under various conditions. Additionally, this expansion is a fundamental step in developing thermodynamic equations and models.

4. Can U be expanded in terms of other variables besides T and V?

Yes, U can also be expanded in terms of other variables such as pressure (P) and moles (n). This is known as the Gibbs-Duhem equation and is often used in chemical thermodynamics. However, expanding U in terms of T and V is more commonly used in general thermodynamic analysis.

5. How does expanding U in terms of T and V relate to the ideal gas law?

The ideal gas law, PV = nRT, is derived from the expansion of U in terms of T and V. By assuming that internal energy is solely dependent on temperature, the ideal gas law can be derived from the first law of thermodynamics. This law is an important tool in studying the behavior of gases and is often used in thermodynamic calculations.

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