Physics · University
Reversible isothermal ideal-gas work
Work is positive for expansion; the process is reversible and isothermal for an ideal gas.
Method and conditions
Work is positive for expansion; the process is reversible and isothermal for an ideal gas.
Wby = nRT ln(Vf/Vi)
Worked examples
An ideal gas of 9 mol expands reversibly and isothermally at 520 K until Vf/Vi=7. Using R=8.314 J/(mol·K), find work done by the gas. Round the final result to 4 decimal places if needed. Answer in J.
Wby = (9)(8.314)(520) ln(7).
75714.4299 J
An ideal gas of 5 mol expands reversibly and isothermally at 540 K until Vf/Vi=6. Using R=8.314 J/(mol·K), find work done by the gas. Round the final result to 4 decimal places if needed. Answer in J.
Wby = (5)(8.314)(540) ln(6).
40221.0582 J
Try it
An ideal gas of 2 mol expands reversibly and isothermally at 200 K until Vf/Vi=6. Using R=8.314 J/(mol·K), find work done by the gas. Round the final result to 4 decimal places if needed. Answer in J.
An ideal gas of 2 mol expands reversibly and isothermally at 280 K until Vf/Vi=6. Using R=8.314 J/(mol·K), find work done by the gas. Round the final result to 4 decimal places if needed. Answer in J.
Check your work
Answers and marking notes
- 5958.6753 J
Wby = (2)(8.314)(200) ln(6).
- 8342.1454 J
Wby = (2)(8.314)(280) ln(6).
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