Expansion work done by/on the system - Problem 8.17

[keyanabogan 2J]

I'm still having a little a trouble on determining whether expansion work is being done by the system or on the system. On problem 8.17 a) it shows that the system is a liquid and the surrounding is a solid, so does the phase state that the system and the surrounding is in act as an indicator on whether work is done by/on the system?

Also, is it okay to assume that when expansion work is done on the system that w is positive and that when expansion work is done by the system that w is negative?

[Anmol Dhaliwal 2C]

The phase state of the system does affect whether work is done on/by the system, such as in a) work is done by the system because there is expansion from a solid to a liquid (liquids are more dispersed in a sense and therefore there is expansion). It is also okay to assume that w is positive when work is done on the system and negative if it is done by the system. (The phase a system changes into indicates whether work is done on or by the system because when converting from solid to liquid, work was done by the system and in b) work was done on the system as it turned from vapor to liquid). Hope this helps!