Solving Enthalpy for Ideal Gas: Finding H as a Function of S and P

  • Thread starter Thread starter quantoshake11
  • Start date Start date
  • Tags Tags
    Gas Ideal gas
AI Thread Summary
The discussion centers on the challenge of deriving the enthalpy (H) for an ideal gas using the equation H=U+PV. The user expresses difficulty in expressing H as a function of entropy (S) and pressure (P), despite finding it straightforward for Helmholtz and Gibbs free energies. A suggestion is made to use the Sackur-Tetrode equation to express entropy in terms of internal energy (U), allowing for inversion to derive U as a function of S. The user acknowledges this approach and realizes they can eliminate volume from the equations using other relations. This exchange highlights the complexities of thermodynamic equations for ideal gases and the utility of established equations in simplifying the process.
quantoshake11
Messages
45
Reaction score
0
Hello.
I'm having troubles solving the enthalpy for an ideal gas.
From the equation H=U+PV, i could find H substituting PV=NRT = U/c, but then i need the energy as a function of S and P, so i'd get H as a function of its proper variables (S and P)..
I can't find such an expression. It's just so easy to find the helmholtz and gibbs representation for ideal gases that i find it odd that this one gives me so much trouble. Wikipedia gives the equation for the enthalpy, but i have no clue how to write it that way :S
could anyone give me some clues to solve this one?
thanks
 
Science news on Phys.org
There's an equation called the Sackur-Tetrode equation that expresses the entropy of an ideal gas S in terms of U. You can invert this to give U in terms of S, then substitute into your equation for H in terms of U and you will have H in terms of S.
 
oh, thanks! i just need to get the volume out of there, but i could use the other relations to do that. doh! i should've seen that earlier :P
 

Thread 'Entropy and configurations of microstates'

I was watching a Khan Academy video on entropy called: Reconciling thermodynamic and state definitions of entropy. So in the video it says: Let's say I have a container. And in that container, I have gas particles and they're bouncing around like gas particles tend to do, creating some pressure on the container of a certain volume. And let's say I have n particles. Now, each of these particles could be in x different states. Now, if each of them can be in x different states, how many total...
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 »

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 »

Similar threads

I Why does an ideal gas satisfy ##(\partial U/\partial P)_T=0##?
Replies
4
Views
3K
I Does Callen's Entropy Expression for a General Ideal Gas Contain an Error?
Replies
19
Views
2K
I Helmholtz entropy of ideal gas mixture is additive?
Replies
3
Views
2K
I Why pressure stays the same when doubling both volume and temperature?
Replies
35
Views
4K
I Obtaining this form for molar energy under virial expansion (Callen)
Replies
23
Views
2K
I State equations for a thermodynamic substance/system
Replies
9
Views
3K
I Cannot understand formula for molar heat capacities of an ideal gas
Replies
22
Views
3K
I Irreversible adiabatic processes & entropy change (clarification needed)
Replies
22
Views
5K
Euler's equation of thermodynamics in free expansion (Joule expansion)
Replies
4
Views
2K
Enthelpy of an ideal gas and pressure
Replies
15
Views
12K

Hot Threads

Recent Insights

Back
Top