Find the equation of state of each gas

  • #1
curious_mind
41
9
Homework Statement
Consider three gases with ##(P_1,V_1),(P_2,V_2)## and ##(P_3,V_3)##. It is found that when the first two are in equilibrium the following condition is satisfied: ##P_1V_1 =\left(P_2 +\frac{a}{V_2^2}\right)(V_2 −b)##, while the equation satisfied when the first and the last are in equilibrium is ##P_3(V_3 −c)=P_1V_1 e^{\frac{−d}{V_3P_1V_1}}##. Find the respective equations of state and identify them.
Relevant Equations
Equation of states of gas at temperature T##f(P,V,T)=0##
The problem is from the book "The Principles of Thermodynamics" by ND Hari dass.

It looks trivial problem, but I am not able to form logical arguements for going into next step.

For example, It seems like first gas has equation of state ##PV =nRT## and second has ## \left( P_2 +\frac{a}{V_2^2} \right) (V_2 −b) = nRT ##
But I cannot straightforward assume Right hand side of equation of state to be simply ##nRT## in general right ? So what could be valid way to proceed from thermodynamical laws ?

Thanks.
 
Physics news on Phys.org
  • #2
For the relationships to hold across all T, each relationship must be of the form (first expression =second expression = some function of T).
 
  • Like
Likes curious_mind
  • #3
If we equate all three relations, then it will be valid only if all three gases in equilibrium, which is not required to be found. We require to find all three gases equation of state separately, at different temperatures.

Also, how can we say that it individual ##f(P,V)## is some function of ##T## ONLY?. Right hand side of equation of state might containt terms like ##\cos (TVe^P)## etc etc or something, in general - right m? Or am I missing something very fundamental?
 
Last edited:
  • #4
curious_mind said:
If we equate all three relations
I did not say that. The "some function of T" does not have to be the same for each.
curious_mind said:
Also, how can we say that it individual ##f(P,V)## is some function of ##T## ONLY?.
It is the same principle as "separation of variables" in PDEs.
We know that ##T_1=g_1(P_1,V_1)## and ##T_2=g_2(P_2,V_12)## for some functions ##g_1, g_2##. So at any given temperature T we know ##g_1(P_1,V_1)=g_2(P_2,V_12)##. And these are the forms you are given.
 
  • Like
Likes curious_mind
  • #5
It seems to me your original approach was correct, except I would assume the V is molar volume rather than volume itself, so you would get rid of the n's in the equations.
 
  • Like
Likes curious_mind

FAQ: Find the equation of state of each gas

What is an equation of state in the context of gases?

An equation of state is a mathematical equation that describes the relationship between pressure, volume, temperature, and the amount of gas. It helps in predicting the state of a gas under different conditions.

What is the ideal gas equation of state?

The ideal gas equation of state is PV = nRT, where P is pressure, V is volume, n is the number of moles, R is the universal gas constant, and T is temperature in Kelvin. This equation assumes no interactions between gas molecules and that the volume occupied by the gas molecules themselves is negligible.

How does the Van der Waals equation differ from the ideal gas equation?

The Van der Waals equation accounts for the finite size of gas molecules and the intermolecular forces between them. It is given by (P + a(n/V)^2)(V - nb) = nRT, where a and b are constants specific to each gas. The term a(n/V)^2 corrects for intermolecular attractions, and nb corrects for the volume occupied by the gas molecules.

What are some other common equations of state for gases?

Other common equations of state include the Redlich-Kwong equation, the Soave-Redlich-Kwong (SRK) equation, and the Peng-Robinson equation. These equations provide more accurate predictions for real gases by incorporating additional parameters to account for molecular interactions and volume.

Why is it important to know the equation of state of a gas?

Knowing the equation of state of a gas is crucial for predicting and understanding its behavior under various conditions. This information is essential in fields such as chemical engineering, thermodynamics, and physical chemistry, where accurate models are necessary for designing processes and equipment.

Back
Top