Kaplan Physics Thermodynamics #9

[El-Rami]

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The question states the following:

A student making a coffee cup calorimeter fails to use a second coffee cup and incompletely seals the lid.

It then goes on to ask what the student's initial goal was and what the result of her mistake was.

I chose A) She was trying to create an isolated system but instead created an open system, but the correct choice was B) She was trying to create an isolated system but instead created a closed system.

Now here's where I disagree with the answer key. It states in the explanation that you have to assume from the question stem that the lid was closed in such a way that matter could not be exchanged with the environment (a closed system); however, the stem explicitly says the lid was incompletely sealed. How does this imply that matter was not permitted to be exchanged? I believe that if it said completely sealed that the answer key would be correct, but can someone please explain how my thinking is incorrect? Thanks.

 

[Quinoline]

From your description alone I'd say your thinking is correct.

 

[MrRed]

If in the question it in fact states that the lid is incompletely sealed this would mean that the system within the single coffee cup can exchange both matter and energy with the environment and is 100% an open system; no two ways about it.

 

[El-Rami]

I suppose it's safe to assume it's a typo, then. Thanks.