I am not disagreeing with any of you on where the equilibrium lies, not on how much ammonia is produced, but the question has to be taken in context. Now the high school class that I have are taking college level chemistry in a special program, thus they are supposed to be ahead of the curve, (their last exam scores might not agree, but that is another issue).
Of course I am making assumptions, however, after reading the thread on high school chemistry books; several of those that were mentioned such as those by Raymond Chang and Zumdahl, are books that we have used or are using. Currently we are using Raymond Chang's 9th edition.
This type of question is typical during the chapter on aqueous solutions, usually chapter 4 or 5 on most current General Chemistry books. The curriculum is divided into double replacement reactions which include precipitation and acid base reactions, and redox reactions, which include the rest including, displacement, combustion, disproportionation, combintaion and decomposition.
For double replacement reactions the students are asked to produce a molecular formula, then separate the molecules into ions to produce the ionic equation, last they are asked to form the net ionic equation by removing ions that did not react, ie are on both sides of the equation. Thus the reaction is condensed into only those ions that produce either a solid (precipitation), water (acid/base) or gases (reactions involving the ammonia/ammonium ions and carbon dioxide/carbonate/bicarbonate ions). If no solids, liquids or gases are formed, then the student is to assume that no chemical reaction took place. Keeping in mind that early on they are told that dissolving salts is a physical and not a chemical process. Thus merely dissolving a salt is not considered a chemical reaction.
Now the question asked was this
"What are the products for this?
NH4Cl + H2O
I really need some help here.
I was told that it's a synthesis reaction but it's not making any sense to me whatsoever and i'm so confused."
As the student prepares the equation the student typically swaps ions
NH4Cl + H2O <----> HCl + NH4OH
Then separating to produce the ionic equation, we have what all of us agree, ammonium and chlorine. However in this form the student assumes that no reaction occurs since only ionic species were produced.
Nonetheless, this reaction, as all of you have mentioned, causes a change in pH in the solution, removes heat (endothermic), and in a few instances, a few students will detect the smell of ammonia.
The student is asked that if the raction did not produce anything other than ions and while the H+ explains the change in pH, the teacher points out that OH is created in equal ammounts thus negating the pH change. Then what caused the observed changes.
If we answer her question in terms of only ammonium and chloride ions, then there are no new products, water is not needed in the equation, then why have it in the first place? And what is the synthesis product, if you already had all the components before the reaction, you did not synthesize anything new.
This reaction, or any example involving the ammonium ion is most often used to explain to students that not all double replacement reactions produce a precipitate or water, but that in a few cases gases are also produced. The same reasoning is used to explain the reaction between CaCO3 and HCl. also a double replacement reaction that produces CO2, granted a more obious one than the one we are discussing. When asked to categorize these types of reactions, they do not fit any of the other models that they are taught.
Thus once again I am not arguing that ammonium and chloride are not produced, nor that they are not produced in large quantities, when compared to the amount of ammonia. And yes you need large molarities to even detect a hint of ammonia, thus the pH change is typically used more often as a means to detect evidence of reaction. And yes evaporating the solution will produce ammonium chloride crystals. Nonetheless, this reaction is a special one in the chapter on aqueous reactions.
One last point, in laboratories, when a lab asks for the students to use ammonia in a reaction, the students are always confused, because they do not have any bottles labeled ammonia, and they always tell me that we forgot to provide it to them. At which point I remind them that we can only use ammonia in the laboratory in the form of ammonium hydroxide, and to use the bottle labeled ammonium hydroxide.
In terms of carrying out the experiment, a few General Chemistry Laboratories, use the preparation of an ammonium chloride solution and subsequent evaporation to demonstrate the law of conservation of mass. However, these labs usually require scales with sensitivity of 0.001, which I am sad to say we do not have in our chemistry lab for students to use.