constant volume/pressure

[oliviabruin24]

What does it mean when a problem says something occurs under contant pressure or constant volume? I know what these mean in a very literal sense, but how can I manipulate an equation if it has a variable in it that I can’t work with? Would I just plug in 0 or 1 for those? Could I omit them completely?

[Chisomaga Azu]

I think it varies based on the question. Sometimes when a question states that a problem occurs under constant volume, it usually is trying to indicate 0 work being done. If it states that the problem occurs under constant pressure, it might be trying to indicate to use the work equation w=p∆v. So it really just depends on the question.

[006248274]

So because its a constant volume, q=change in internal energy because when there is no change in volume, no work is being done(-p delta V=0 bc delta V=0), so the equation delta U(internal energy)=q+w just becomes delta u=q. Then, because the definition of enthalpy, H=q+pv. Since v is 0, H= q at constant volume, and because delta u=q, then delta u also=H at constant volume