Energy Change in a Closed System

[Isabelle Preston 2C]

The most recent example, in the 2/3 lecture, was talking about a change in the number of moles in a system. I might be missing something, but is a change in moles in a closed system always due to a reaction, therefore a decrease in moles of other substances?

Is finding q and w always ΔH and PΔV respectively, or how else are they found other different conditions?

[Matthew Bolton 3L]

A closed system would by definition have a fixed amount of matter. As you have suggested, the amount of moles of a particular substance will not change unless it undergoes a reaction.

In terms of finding work in a system, P∆V would be used for the expansion of a gas. A table from the textbook in Section 4A.3 outlines the appropriate variables for certain circumstances.