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.

 

[PJC01]

The main difference between a bomb calorimeter and a coffee cup calorimeter is the way in which they measure heat. A bomb calorimeter is designed to measure the heat released or absorbed during a chemical reaction at a constant volume, while a coffee cup calorimeter measures the heat change at a constant pressure.

The bomb calorimeter is a closed container that is sealed and insulated, meaning that there is no exchange of matter or heat with the surroundings. This allows for the volume to remain constant during a reaction, as no gases or other substances can escape. On the other hand, a coffee cup calorimeter is an open system, meaning that there is a constant exchange of matter and heat with the surroundings. This allows for the pressure to remain constant, as any gases produced during the reaction can escape into the surrounding atmosphere.

Additionally, the design of the bomb calorimeter allows for the pressure to increase as the reaction takes place, due to the production of gases. This increase in pressure is accounted for in the calculation of heat released or absorbed. In a coffee cup calorimeter, the pressure remains constant as any gases produced are allowed to escape.

In summary, the difference between a bomb calorimeter and a coffee cup calorimeter lies in the ability to maintain a constant volume or pressure, respectively, during a reaction. This is achieved through the design of the containers and the exchange of matter and heat with the surroundings.