[EX5TASY]

For some reason, I can't get this problem!!!


A 0.2250 g sample of vanillin (C8H8O3) is then burned in the same calorimeter, and the temperature increases by 3.11°C. What is the energy of combustion per gram of vanillin?

A prior question gave me the heat capacity of the calorimeter to be 1.69 kJ/°C.



So this is what I did using this equation:

Heat evolved by reaction = specific heat capacity X mass of solution X increase in temperature

= 1.69kJ/°C x 3.11°C = 5.2559kJ

Then I take it divided by grams to get kJ/gram.
5.2559kJ / 0.2250g = 23.3595kJ/g

But this answer is not right...Am I missing something?

[allanf]

It looks right to me, could the heat capacity be wrong?

[thegoodaaron]

Your problem is that the sign of your answer is not correct. The vanillin is burned causing an increase in temperature. Thus, the reaction is exothermic and the sign of the answer should be negative.

[EX5TASY]

oh geez.. i feel stupid 

thanks