Why is NH4NO3 dissolved in water an endothermic reaction?

[PocketRocket]

In general, is the solubility of salts in water an endo or exo reaction or does it depend? Thanks

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[FeralisExtremum]

It depends on the identity of the substance. Usually dissolving solids in a liquid is endothermic.

 

[100%permwinner]

Gen chem review: Consider solute + solvent -->solution
ΔHsolution = ΔH(separating solvent molecules >0) + ΔH(separating solute molecules >0) + ΔH(mixing solute and solvent molecules <0)
ΔHsolu > 0, endothermic, system warms, surrounding (i.e. air, beaker, test tube) cools (ex. NH4NO3 in H2O); ΔHsolu < 0, exothermic, system cools (ex. diluting strong acid/base in H2O)
ΔHsolu depends on the relative strengths of ΔHseparating and ΔHmixing, which depends on the properties of particular solutes and solvents used in the reaction.

 

[DAT Destroyer]

Gen chem review: Consider solute + solvent -->solution
ΔHsolution = ΔH(separating solvent molecules >0) + ΔH(separating solute molecules >0) + ΔH(mixing solute and solvent molecules <0)
ΔHsolu > 0, endothermic, system warms, surrounding (i.e. air, beaker, test tube) cools (ex. NH4NO3 in H2O); ΔHsolu < 0, exothermic, system cools (ex. diluting strong acid/base in H2O)
ΔHsolu depends on the relative strengths of ΔHseparating and ΔHmixing, which depends on the properties of particular solutes and solvents used in the reaction.

The process of dissolving can be endothermic (temperature goes down) or exothermic (temperature goes up). When water dissolves a substance, the water molecules attract and “bond” to the particles (molecules or ions) of the substance causing the particles to separate from each other. The “bond” that a water molecule makes is not a covalent or ionic bond. It is a strong attraction caused by water’s polarity. It takes energy to break the bonds between the molecules or ions of the solute. Energy is released when water molecules bond to the solute molecules or ions. If it takes more energy to separate the particles of the solute than is released when the water molecules bond to the particles, then the temperature goes down (endothermic). If it takes less energy to separate the particles of the solute than is released when the water molecules bond to the particles, then the temperature goes up (exothermic).

You would NOT be asked if a particular salt is endothermic or exothermic...... HOWEVER,,,,,make sure that you remember,,,,,if a reaction is EXOTHERMIC.....the surroundings get HOT......if the reaction is endothermic,,,,,,, surroundings get cold !.......If you bruised your knee.......and put an NH4NO3 pack on it........it felt COLD !!!!!! An endothermic reaction took place.





Hope this helps

Dr. Romano

 

[100%permwinner]

Nice insights Dr. Romano. Thanks.

 

[PocketRocket]

The question to which this pertained was ;
"Which of the following is correct?"
a. Temp is a measure of Average kinetic E
b. 30 ml of water at 70 C has a greater average kinetic energy than 50 ml of water at 40C
c. When solid NH4NO3 is dissolved in water at 25C, the solution temp decreases. This reaction is endothermic.
d. A and B
e. All are correct

I knew a and b are correct. What I was wondering about option C during the question was, why couldn't it be exothermic with the solution getting hotter. In other words, how was I supposed to know the solution of NH4NO3 is endothermic as opposed to exothermic. I guess I wasnt sure what the question was alluding to with that answer choice.

As always, thank you orgoman22, your help is greatly appreciated!