**1. The problem statement, all variables and given/known data**

This is for a chemistry report. This is the task:

"Determine the molar enthalpy change for the decomposition of sodium hydrogen carbonate into sodium carbonate, CO(2) and water.

2NaHCO_{3} -> Na_{2}CO_{3} + CO_{2} + H_{2}O

This enthalpy change cannot be measured directly".

Instead, we reacted NaHCO_{3} and Na(2)CO(3) in separate containers with HCL (in excess (100 mL), about 1M).

We measured the temperature changes, and the masses of each solid/liquid.

For the NaHCO_{3} reaction:

Mass(NaHCO_{3}): 0.001021 kg ± 0.000001 kg

Mass(HCl): 0.100 ± 0.001 kg

Change in T = 1 K

For the Na_{2}CO_{3} reaction:

Mass(Na_{2}CO_{3}): 0.000905 kg ± 0.000001 kg

Mass(HCl): 0.100 ± 0.001 kg

Change in T = -0.3 K

**2. Relevant equations**

Nr 1: 2NaHCO_{3} -> Na_{2}CO_{3} + CO(2) + H2O

Nr 2: NaHCO_{3} + HCl -> NaCL + CO_{2} + H_{2}O

Nr 3: Na_{2}CO_{3} + HCl -> 2NaCL + CO_{2} + H_{2}O

Note: By multiplying equation 2 by two, reversing equation 3, and then adding them together, we get equation 1. This has to be done to the

**3. The attempt at a solution**

My biggest problem is figuring out how to find the **Molar** Delta H in kJ/mol. By doing the following, I can calculate the approximate Delta H (only in kJ) for reaction 1:

Following the equation of Heat = Mass * Specific Heat (c) * Delta T, we get:

(Note, here I add the two masses of HCl and the solids, and then use the specific heat of water. I understand this holds quite a large uncertainty. If anybody has a better idea, please say so. I am also really unsure on what I do after calculating the heat, ie. when I invert the sign of the heat form + to - and vica versa. Is this correct?)

For NaHCO_{3}:

Mass = 0.101021 kg

Specific Heat (water) 4186 J/(kg * K)

Delta T = 1 K

Heat = 422.87 J. As this is an exothermic reaction, it becomes -422.87 J

For Na_{2}CO_{3}:

Mass = 0.100905 kg

Delta T = -0.3 K

Heat = -126.71 J. As this is an endothermic reaction, it becomes +126.71 J.

Then, by doing the same to these numbers as is mentioned in Part 2 (the reactions), I end up with (-422.87 * 2) + (126.71*-1) = -970.71 J = -0.971 kJ!

But this however, is just the enthalpy change for the reaction. Not the *molar* enthalpy change...

Any comments on this would be absolutely wonderful, and greatly appreciated!