Work done on/by system?

[AequitasEquitas]

---

Members don't see this ad.

I'm a bit confused on the sign convention used when dealing with the work done by the system or work done on the system and how it relates to internal energy...can anyone tell me if the following statements are true or false and explain why? I'm using the chemistry definition here, assuming E = Q + W

True or False?

The internal energy of a system decreases when work is done on the system

The internal energy of a closed system can be changed by heat flowing into or out of the system.

The internal energy of an isolated system can be changed by heat flowing into or out of the system.

The internal energy of a system decreases if heat flows from the surroundings to the system

 

[AequitasEquitas]

Oops forgot to post my answers and my reasonings to these...

1) False. The internal energy increases (E&#8593😉 because when work is done ON the system W > 0 therefore E = q + W and as W increases, E increases. Here work is done on the system is like thinking of a piston compressing on a gas...right? The surroundings (piston) are doing work on the system (gas molecules) increasing the internal energy.

2) True. Again E = q + W. So increasing heat into the system means that E ↑

3) False?. This defies the definition of an isolated system...right? Heat CANNOT flow/out of the system if it is truly an isolated system.

4) False? If heat flows from the surroundings and into the system then Q > 0. If Q > 0 then E = Q + W, that would mean that internal energy (E) has to increase.

Please correct me if I'm wrong here? Thank you!

 

[jtran7]

thats the way i understand it as well