Calculate the work done by an ideal gas.

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SUMMARY

The discussion focuses on calculating the work done by an ideal gas during two distinct processes: an isochoric process at constant volume and an isobaric process at constant pressure. The initial conditions include 1 mole of gas at 7 atm pressure and 6L volume, with an internal energy of 508 J. The gas is cooled to 1 atm at constant volume before expanding to 8L at constant pressure, resulting in an internal energy of 814 J. The work done by the gas can be calculated using the formula Work = P * ΔV, with careful attention to the pressure values and the appropriate conversion to SI units.

PREREQUISITES
  • Understanding of ideal gas laws, specifically PV = nRT
  • Knowledge of thermodynamic processes, particularly isochoric and isobaric
  • Familiarity with work calculations in thermodynamics, including Work = P * ΔV
  • Ability to convert pressure from atm to Pa and volume from L to m³
NEXT STEPS
  • Study the derivation and application of the ideal gas law (PV = nRT)
  • Learn how to construct and interpret P-V diagrams for thermodynamic processes
  • Explore the integral form of work done in thermodynamics: Work = ∫ P dV
  • Investigate the relationship between internal energy changes and work done in thermodynamic systems
USEFUL FOR

This discussion is beneficial for students studying thermodynamics, particularly those tackling problems related to ideal gases, as well as educators seeking to clarify concepts of work and energy in gas processes.

miamirulz29
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Homework Statement


1 mole of an ideal gas is at 7 atm pressure, occupies 6L and has an internal energy of 508 J. the gas is first cooled at constant volume until its pressure is 1 atm. It is then allowed to expand at constant pressure until its volume is 8L with an internal energy of 814 J. Calculate the work done by the gas. Answer in units of J.

Homework Equations


Work = P * DeltaV
PV = nRT
Work = nRT

The Attempt at a Solution


I tried doing the last equation, but I do not know the temperature. For P*V, which P do I use, the 7atm or 1 atm? I know I have to convert to Pa and the m^3.
 
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A simple way to start the question would be to draw a P-V diagram. The work done by the gas/on the gas is simply the area underneath the graph depicting the changes (after adjusting for the appropriate sign).
Otherwise, you should break up the process into two parts: the isochoric (constant volume) and the isobaric (constant pressure) processes. Then, compute the work done by/on the gas for each part.

By the way, P \Delta V is definitely not equal to PV! The work done by the gas in an infinitesimal step is equal to the pressure multiplied by the change in volume. The equation Work = P \Delta V is true only for constant pressure; for general cases, we have to employ the integral Work = \int P dV with the appropriate boundaries.
 

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