Evaluating An Enthalpy Change That Cannot Be Measured Directly. We were told that sodium hydrogencarbonate decomposes on heating to give sodium carbonate, water and carbon dioxide as shown in the equation below:- 2NaHCO3(s)--------> Na2CO3 (s) + H2O (l) + CO2 (g) = DeltaH1 This was given as deltaH1 and we had to calculate as part of the experiment. This however cannot be measured directly, but can be found using the enthalpy changes from two other reactions. These being that of sodium hydrogencarbonate and hydrochloric acid and also sodium carbonate and hydrochloric acid. We were given a list