Adiabatic expansion of a monatomic gas

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SUMMARY

The discussion focuses on the adiabatic expansion of a monatomic gas described by van der Waals' equation. The molar energy equation is defined as E = (3/2)RT - a/V, where R is the universal gas constant, T is temperature, V is volume, and a is a constant. The user seeks to determine the final temperature T2 after the gas expands from volume V1 to V2 in a vacuum, while grappling with the integration of terms derived from the van der Waals' equation. The key equations involved include the van der Waals' equation P = RT/(V - b) - a/V^2 and the relationship between work and energy in an adiabatic process.

PREREQUISITES
  • Understanding of van der Waals' equation and its implications on gas behavior.
  • Knowledge of thermodynamic principles, particularly adiabatic processes.
  • Familiarity with calculus, specifically integration techniques for differential equations.
  • Basic concepts of molar energy and its relation to temperature and volume in gases.
NEXT STEPS
  • Study the derivation and applications of van der Waals' equation in real gas scenarios.
  • Learn about the principles of adiabatic processes and their mathematical representations.
  • Explore integration techniques for solving differential equations in thermodynamics.
  • Investigate the implications of molar energy changes in monatomic gases during expansion.
USEFUL FOR

Students and professionals in physics and engineering, particularly those studying thermodynamics and gas laws, will benefit from this discussion. It is especially relevant for those tackling problems involving real gases and adiabatic processes.

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Homework Statement



The molar energy of a monatomic gas which obeys van der Waals' equation is given by

E = (3/2)RT - a/V

V volume, T temperature, a is a constant. Initially you have T1 at V1, and the gas expands adiabatically in a vacuum so that you have V2. What is T2?

Homework Equations



Van der Waals' equation: P = RT/(V - b) - a/V^2

The Attempt at a Solution



Q = 0, so dW = dE. dW = -PdV, and I rewrite P in terms of V and T according to van der Waals' equation, then try to rearrange terms so that I can integrate, but I don't think the terms are separable, and I'm beginning to wonder if there is something wrong in my approach. Any help would be appreciated.
 
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You have [itex]dE = (3R/2)dT + (a/V^2)dV[/itex] and you can also write an expression for RdT from the VdW equation. Plug in for RdT from the second into the first, and set dE + PdV = 0. This should leave you with a DE in (P,V). What does it look like? Is this the equation you say is not separable?
 

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