Verify Thermochemistry answer (no calculations)

[ace123]

I just want to make sure my logic is correct.

Hot coffee in a vacuum flask (thermos) is an example of what type of sytem?

Choices:

Closed
Open
Isolated


I thought it was closed system because the coffee is not interacting with the surroundings. But one of my classmates said he thought it was open because it's interacting with the flask. So which one of is correct?

Edit: I know believe it's isolated because heat is not exchanged. at least I don't think it is

 

[eli64]

heres my .02 (too much fun to stay away :) )

open or closed? depends on if the lid is on and tightened on the flask

the system is the coffee, the flask (and its vacuum ) is the boundary, the surroundings is the rest of the universe outside of the flask.

open if the lid is not on
closed and isolated if it is on and closed tight

 

[ace123]

Yea we don't have that much information. But apparently it was isolated because heat it not transfered. So thank you for your .02

 

[Gokul43201]

Definitely isolated - no mass transfer and no energy transfer.