Question about thermodynamics first law

AI Thread Summary
The discussion clarifies that the equation dU = TdS - PdV is not limited to reversible processes but is a fundamental relationship applicable to any thermodynamic state. It emphasizes that this equation reflects the physical properties of a material, linking changes in internal energy (U), entropy (S), and volume (V) between neighboring equilibrium states. The relationship is derived from the second law of thermodynamics, which establishes constraints on these state functions. Despite being developed from reversible processes, the equation's applicability extends beyond them. Overall, the key takeaway is that dU = TdS - PdV is a state function relationship, independent of the process type.
Clara Chung
Messages
300
Reaction score
13
I know that dS=dQ/T for reversible process,
is dU=TdS-PdV for reversible process only?
 
Science news on Phys.org
Clara Chung said:
I know that dS=dQ/T for reversible process,
is dU=TdS-PdV for reversible process only?
This equation has nothing to do with any process. It is a physical property relationship that must be satisfied for any material, describing the relationship between the mutual changes in U, S, and V between and two closely neighboring thermodynamic equilibrium states of the material. This constraint is imposed as a consequence of the 2nd law of thermodynamics.
 
  • Like
Likes Clara Chung
Agree with Chestermiller, dU = TdS-pdV is nothing to do with the process, (reversible or irreversible), even though it is developed from the reversible process, since all of the qualities here are state functions. Therefore, they are just related to the state.
 

Thread 'Condensate rate of water for an air conditioning cooling coil'

I need to calculate the amount of water condensed from a DX cooling coil per hour given the size of the expansion coil (the total condensing surface area), the incoming air temperature, the amount of air flow from the fan, the BTU capacity of the compressor and the incoming air humidity. There are lots of condenser calculators around but they all need the air flow and incoming and outgoing humidity and then give a total volume of condensed water but I need more than that. The size of the...
View full post »
Thread 'Why work is PdV and not (P+dP)dV in an isothermal process?'

Thread 'Why work is PdV and not (P+dP)dV in an isothermal process?'

Let's say we have a cylinder of volume V1 with a frictionless movable piston and some gas trapped inside with pressure P1 and temperature T1. On top of the piston lay some small pebbles that add weight and essentially create the pressure P1. Also the system is inside a reservoir of water that keeps its temperature constant at T1. The system is in equilibrium at V1, P1, T1. Now let's say i put another very small pebble on top of the piston (0,00001kg) and after some seconds the system...
View full post »

Similar threads

I Minimization of the Gibbs energy when number of molecules varies
Replies
16
Views
2K
I Understand the Thermodynamic Identity: Is This Correct?
Replies
3
Views
2K
I Reversible / Irreversible Fundamental Equation
Replies
3
Views
1K
I Why is ##dQ = dH## still valid for chemical reaction (Callen)?
Replies
31
Views
2K
I First law of thermodynamics -- two different expressions for dQ
Replies
23
Views
2K
I Elementary Ideas About Entropy -- Is this textbook example correct?
Replies
16
Views
2K
I An experiment against the second law of thermodynamics
Replies
37
Views
4K
I Application of the first law of thermodynamics
Replies
46
Views
6K
B Entropy change for reversible and irreversible processes
Replies
12
Views
2K
Why does the entropy of a closed system remain constant in a reversible process?
Replies
10
Views
3K

Hot Threads

Recent Insights

Back
Top