[govibe]

I have this bomb calorimeter problem:
"Under constant-volume conditions the heat of combustion of benzoic acid, HC7H5O2, is 26.38 kJ/g. A 1.600 g sample of benzoic acid is burned in a bomb calorimeter. The temperature of the calorimeter increases from 22.45°C to 26.10°C.

    (a) What is the total heat capacity of the calorimeter? Units:kJ/°C
    (b) If the calorimeter contained 1.200 kg of water, what is the heat capacity of the calorimeter when it contains no water? Units: kJ/°C
    (c) What temperature increase would be expected if the 1.600 g sample of benzoic acid were combusted when the calorimeter contained 1.000 kg of water?"

I tried doing A first... I used the equation delta H=MC delta T... I plugged in 1.6000 for mass, 3.65 degrees as T and C as 26.38KJ... Since heat capacity is heat absorbed divided by increase in temperature, I divided 154.0592/3.65 which is 42.2 KJ/C, but that is wrong... what did I do wrong?

B and C I'm not sure of at all because I don't know how water affects the temperature...

[DrCMS]

First calculate the heat released in kJ by the combustion of 1.6g of benzoic acid.  Hint - The temp rise is not needed here

Take that heat released value and calculate the heat capacity of the calorimeter.  The temp rise is needed here.

Calculate the energy absorbed by 1.2kg of water going from 22.45 to 26.10°C.  Take this figure away from the one above to get the heat capacity of the empty calorimeter.

Add the heat capacity of 1kg of water to the empty calorimeter figure to work out the new heat rise.

[govibe]

I'm still having trouble understanding the last part (part c)... How do you figure out the change in temperature from a specific heat?

[Padfoot]

I'm still having trouble understanding the last part (part c)... How do you figure out the change in temperature from a specific heat?

Write an eqn for delta H in this situation keeping in mind the heat capacity of the calorimeter.  Use the specific heat of water to take into account the energy absorbed by the water.  Your expression should include Temp change, which you can solve for.

[govibe]

how do you know what delta H is?

[Padfoot]

See Original question and DrCMS's post.