[LHM]

I know this is a really basic question, but why do bomb calorimeters have heat capacities? I'm just kind of used to coffee-cup calorimeters and how they supposedly don't exchange any heat with the surroundings because the water absorbs the heat. So since a bomb calorimeter is supposed to be more complicated and everything, how does it evolve heat?

[Borek]

I feel like you are mixing different things. It doesn't evolve heat, it doesn't exchange heat with surroundings.

[opti384]

The basic concept of calorimeters will be shutting off heat exchange with the system and the surrounding.

[LHM]

Since that's true, then why do you have to add 783*(26.01-23.73) to 4.184*254*(26.01-23.73) to get the right answer in this question?

A bomb calorimeter has a heat capacity of 783 J*^oC^-1 and contains 254 g of water, which has a specific heat of 4.184 J*g^-1*^oC^-1. How much heat is evolved or absorbed by a reaction when the temperature goes from 23.73*^oC to 26.01*^oC?

A) 1.78 kJ absorbed
B) 2.42 kJ absorbed
C) 1.78 kJ evolved
D) 4.21 kJ evolved


The correct answer is D, which is what you get when you add the 2 parts I had above. I was just confused as to why the heat capacity of the bomb calorimeter mattered.

[opti384]

4.21 KJ will be the heat from the reaction taking in the bomb calorimeter. The water and the bomb calorimeter absorbs the heat and that is why we use the heat capacity and specific heat.