closed vs open systems

[dat_student]

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I don't understand this Kaplan's argument:

test #2, q 54

Kaplan says:
1) "...a closed thermal system is impermeable to the exchange of matter. Thus, it can only exchange energy but not matter with its surrounding.."
2) "... A system that can exchange both energy and matter with its surrounding is known as open system ..."

Doesn't the second statement contradict the 1st statement?

 

[gatszu]

nope! how does the 2nd statement contradict the 1st? key word is "closed thermal."

 

[dat_student]

nope! how does the 2nd statement contradict the 1st? key word is "closed thermal."

I felt "closed X" means "X" is not exchanged with the surrounding (i.e. X is conserved).

Based on #1, "closed thermal" implies that the only thing that's not closed (conserved) is thermal.

 

[cowsgomoo]

An isolated system is the only system that is completely closed for both energy and matter.

 

[puncho]

isolated - no exchange of matter or energy
closed - no exchange of matter
open - free exchange of matter and energy

 

[fannian]

Does anyone else here get confused by work done on a system or work done by a system? And what is the best way to memorize the signs of each? The equation (I think) is,

E = q + w

When is w pos or neg? When heat is added to the system, q is pos, and when heat is released into the surroundings, q is neg - right? But what about sign changes for w? And does anyone know any way to memorize this?

 

[dat_student]

isolated - no exchange of matter or energy
closed - no exchange of matter
open - free exchange of matter and energy

so, is a closed-thermal-system the same as a closed-system?