Bomb calorimeter and coffee cup calorimeter

[gkangelexa]

What is different between a bomb calorimeter and a coffee cup calorimeter that makes one only constant volume and the other only constant pressure?

to me, it seems that both of them should have constant volume because they are both closed containers...

and why is the pressure in a coffee cup calorimeter constant?

What am I missing?

thanks!

 

[cjl]

Because usually, a coffee cup is not sealed well enough to actually contain pressure.

 

[gkangelexa]

so that means it stays at atmospheric pressure, which is constant...!

 

[cjl]

Exactly.