Heat of combustion of ethanol from calorimeter data

[Owelode]

Calorimetery Problem. :( It's not a homework but I can't get the answer.

0.510 g of ethanol is burned in a flame calorimeter (constant pressure) containing 1200 g of water. The water is initially 22.46 C and is warmed up to 25.52 C as a result of the reaction. The heat capacity of the calorimeter is 10.4 kJ/ C. What is the change in enthaply for the combustion of ethanol? Also, calculate the heat released when 73.5 g of ethanol undergoes combustion.

 

[pzona]

Show an attempt at a solution? Relevant equations? Anything?

 

[Owelode]

I did attempt it on my own. I was hoping someone would explain it to me though.


I used Q(rxn) = Q(water) + Q(calorimeter)

Also expanded: Q (rxn) = -[(m*s*change in temp.) + (C*change in temp.)]
= -[(1200*4.184*3.06) + (10400*3.06)] <---- I changed things from joules to kJ

And then I am lost from there. I got 47.22 KJ

 

[Borek]

Seems to me so far you are doing fine. 47.22kJ per how much ethanol? It will be better to list it either per gram or - even better - per mole. And watch the sign.

--

 

[pzona]

Your solution looks good so far, you're almost there. What equations do you know that include enthalpy and energy?