Heating a gas against an external pressure while keeping volume constant yields work done equal to__________________?
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Answer: C. zero
Explanation
Work done in thermodynamics is defined mathematically as the integral of pressure multiplied by volume change. During an isochoric process where volume remains constant, the volume change differential equals zero. Multiplying pressure by a zero volume change results in zero boundary work done by the system. Isochoric processes occur inside rigid closed containers where boundaries cannot move outward. Any heat added to a gas at constant volume increases its internal energy and temperature instead of doing work. P-V diagrams represent constant volume processes as vertical lines with zero horizontal width.
Rigid pressure cooker vessels heat water without performing any mechanical boundary work. Internal combustion engine combustion phases are often approximated as constant volume heat additions. Calculating system energy balances requires recognizing when boundary work terms evaluate to zero. A positive work value implies expansion against a moving boundary, which cannot occur at constant volume. Negative work indicates compression work input, which also requires a change in system volume. Multiplying pressure by volume directly calculates energy units but does not represent differential boundary work.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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