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When a system is isobaric that means that the pressure is constant, which implies that . I think this is all you can assume from this statement. Dr. Lavelle didn't really talk specifically about the terms isobaric and isochoric, so I wouldn't worry too much about it.
Isobaric is constant pressure, isochoric is constant volume, and isothermal is constant temperature. With these conditions, you'll need to match up the right equations with each one. There are reversible and irreversible equations.
During Lyndon and Matt's Pizza Rolls review session, Matt made a comment that might help with remembering the meaning of isobaric. He emphasized the BAR in isoBARic and compared it to BARometer, which is an instrument used to measure atmospheric pressure. Hope this helps!
When pressure is constant, ΔH=q. This is because ΔH=ΔU+PΔV. Since ΔU=q+w, the equation can be rewritten as, ΔH=q+w+PΔV. Since w=-PexΔV, that equation can be rewritten as ΔH=q-PexΔV+PΔV. P=Pex in isobaric conditions so ΔH=q. Therefore, Cp=ΔH/ΔT under these conditions.
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