why does NH4NO3 decrease solution temperature

[suhshi]

can someone explain why when NH4NO3 is dissolved in water, the solution temp decreases and its endothermic.
I thought according to the phase diagrams, when temperature decreases you release energy.

and why does NH4 NO3 make a solution colder?

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[doc3232]

I would guess its because there is an increase in entropy (solid is dissolved).

deltaG = deltaH - TdeltaS
If S (entropy goes up) then T must go down to maintain the balance.

EDIT: on second thought...I have no idea. It should release heat when it dissolves because it is favorable. sorry

 

[dentrilla]

temp goes down in a endothermic reaction. the reaction is ABSORBING energy and using it up. when u USE the energy(heat), you lose it

EDIT: didn't mean for that too sound like i KNEW it haha, cause i dont, thats just my 2 bits

 

[doc3232]

Ok, I think I know why now. I think my last post was the insignificant entropical effect. The main one is that it requires energy to break up the particles from each other (as it dissolves). Sort of what the post above me said.

 

[UCB05]

can someone explain why when NH4NO3 is dissolved in water, the solution temp decreases and its endothermic.
I thought according to the phase diagrams, when temperature decreases you release energy.

and why does NH4 NO3 make a solution colder?

My guess would be that due to some intramolecular bonding interactions, NH4NO3 has less enthalpic character than its solvated ions in solution.

When it dissociates, the individual ions increase in enthalpy, gaining heat by taking it from its surroundings (the solution). This decreases the temperature of the solution.

Whenever I read a question like this, I think back to high school. My teacher put a wetted beaker of water on a wood plank, then dissolved some NaOH. The dissociation of NaOH is so endothermic that is freezes the beaker to the piece of wood.