Re: Ammonium Nitrate and decommposition

Brandon:

     This is a really good question, and we are excited to see that you 
are thinking about the effect of external environment on a process 
(decomposition) from a thermodynamic perspective.

     There are really two major answers to your question, the first is on 
the thermodynamics of decomposition, and the second, is on specifically 
what you did to shift this process.

     The short answer is that decomposition is a complex process, which is 
predominately biochemical in nature, not a strict thermodynamic 
decomposition of complex molecules into simpler ones.  As such, it has 
virtually thousands of individual chemical reactions that occur, some 
with positive free energy, some with negative, which are coupled to 
others.  Overall, though the process of decomposition is exothermic, a 
large portion of the chemical energy is converted to heat.  Also, the 
activity that occurs is not at equilibrium, but rather steady-state.  
There is a lot of chemical energy in tissue, and organisms such as fungi 
and bacteria are consuming that during decomposition, which is where the 
heat (exothermic) comes from.
 
     The problem arises when you are changing the system to measure the 
effect on this exo/endothermic activity.  As I see it, there are two ways 
in which you could accomplish this, A.) by reducing the temperature of the 
environment, or B.) coupling the decomposition to a chemically endothermic 
reaction, like you did with Ammonium Nitrate/H2O.
     The issue here is that changes in the rate of decomposition are 
primarily dictated by the biological activity of the saprophytes, not 
simply thermodynamics.  Reducing the temperature will slow the growth of 
these organisms, inhibiting decomposition from a general thermodynamic 
slow-down, not so specific to exothermic inhibition.  This is exactly why 
we refrigerate and freeze food, to prevent spoilage.
     Using ammonium nitrate as a proxy for endothermic activity is clever, 
but unfortunately in this case, you will likely see effects due to the 
nitrate itself.  Nitrate chemicals have been used for centuries as 
preservatives, because they have antimicrobial and antifungal activity.  
Just check the ingredient list on any lunch meat, salami, sausage, bacon, 
etc.  Sodium, or potassium nitrate/nitrate is often used in the curing 
process to retard growth.

I hope this helps your quest.  I think with this information, you might be 
able to reformulate your question (hypothesis) and still extract useful 
data from the work you have done.