# Enthalpy of formation of ammonium bicarbonate

I'm helping with correcting lab reports, and one of the experiments the students did was heating of ammonium bicarbonate, $\ce{NH_3HCO_3}$ in powder form, over Bunsen burners, which turns the compound into water, carbon dioxide and ammonia (all gasses). They are supposed to say, in their report, whether this is an endothermic or exothermic reaction.

Now, I would be very surprised if this reaction turned out to be exothermic. An hour of googling seems to agree with me, but I can't find a definite answer. In the course we've talked about enthalpy of formation and Gibbs free energy, so it would fit into the curriculum if we could find the relevant data.

Unfortunately, it's apparently very difficult to find the enthalpy of formation of sodium bicarbonate through google. Many small tables do not list the chemical at all, and the other sources that I've found does not list enthalpy of formation. I've found one number, which is -32 kcal, without specifying whether it's per mole, g, kg, ounce or pound.

Does anyone have a source on the enthalpy of formation of solid $\ce{NH3HCO3}$ at room temperature?

• This becomes $-10.836 kJ/g$, and, without being too picky on atomic weights, $-845 kJ/mol$. Compared to the values for ammonia, water and carbon dioxide given on wikipedia, we can now conclude that the reaction is endothermic. Thank you. – Arthur Oct 27 '16 at 18:55