A gas expands against a piston while a heater keeps the pressure constant throughout the process. What is this kind of process called, and what is the work done by the gas?
AAn isochoric process, doing zero work on the piston
BAn isobaric process, doing work equal to P times ΔV
CAn isothermal process, doing work equal to nRT overall
DAn adiabatic process, doing work drawn from internal energy
Answer & Solution
Correct answer: B. An isobaric process, doing work equal to P times ΔV
1. A process that keeps pressure constant while a gas does work on a piston is defined by the source as an isobaric process.
2. Because the force from a constant pressure is also constant, the work done works out to W = PΔV for this kind of process.
3. An isochoric process instead holds volume fixed, which is the opposite situation described here, ruling out option A.
4. Isothermal and adiabatic processes are defined by constant temperature and by zero heat transfer respectively, neither of which matches a process defined by constant pressure, ruling out options C and D.
_Source: OpenStax College Physics (CC BY 4.0), Ch 15 "Thermodynamics", section 15.2 The First Law of Thermodynamics and Some Simple Processes_
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