Enthalpy changes?

Question

How do u find the enthalpy of decomposition of NaHCO3 from experimental data? Here's what I did:

1) Reacted NaHCO3 with HCl
2) Then, I reacted Na2Co3 with HCl

Mass of NaHCO3 used = 0.00352 kg
Mass of Na2CO3 used = 0.0028 kg
delta T for (NaHCO3-HCl) reaction = -7.5 K
delta T for (Na2CO3-HCl) reaction = 5.5 K
Specific heat capacity of water = 4200 JKg^-1K^-1

Answer 1

You haven't quoted the volume (mass) of solution heated in each case. This is rather important!
Do a q = m x c x deltaT calculation for each reaction, making sure that, for m, you put in the mass of solution being heated.
Then divide each one by the number of moles of either NaHCO3 or Na2CO3 reacting.
Then you will have to divide the value for Na2CO3 by 2, and subtract it from the value for NaHCO3.