Help with this statement, Gen Chem

[Skateguitar]

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"When solid NH4NO3 is dissolved in water at 25 degrees C, the solution temperature decreases. This reaction is endothermic."

Why is it true? I thought since the solution is losing heat, becoming colder, then it would be exothermic.

 

[Avery07]

An exothermic reaction releases heat and would therefore increase the temperature of the surroundings.

Since the reaction is endothermic, it requires an input in energy (heat). This in turn decreases the temperature of the solution.

The solution is losing heat TO dissociate NH4 and NO3 (which in turn gain the heat, or energy). An endothermic process.

 

[Ibraiz]

This is how I remember questions like this.
If the solution became warm (increase in temperature) that means it lost heat i.e. release of heat = exothermic.
If the solution became colder (decrease in temperature) that means it gained heat i.e absorbtion of heat = endothermic

In this question the solution decreased in temperature that means it is endothermic.

 

[MowgliR]

Pretty much when you say endo- or exothermic, you are referring to the surroundings?

 

[Avery07]

Pretty much when you say endo- or exothermic, you are referring to the surroundings?

Not necessarily. You might see a reaction where they don't even mention the temperature of the surroundings. Something like..

A + B + 1050KJ ----> AB

You should be able to identify that this reaction is endothermic as it required an input of energy. If you notice that energy is going in, you should assume that the surroundings of the reaction are getting cooler as they are loosing energy (heat) to form that bond.

AB ----> A + B + 1050KJ

Now this reverse reaction on the other hand, is exothermic. You can see that energy is released. The release of energy would increase the temperature of the surroundings. Heat and energy, in most cases, are synonymous with each other.

 

[Skateguitar]

I get it, I should look at these problems relative to the surroundings. Exothermic would realease heat, increasing the T of the surroundings.
Endothermic would absorb heat, lowering the T of the surroundings.

 

[Ibraiz]

I get it, I should look at these problems relative to the surroundings. Exothermic would realease heat, increasing the T of the surroundings.
Endothermic would absorb heat, lowering the T of the surroundings.

👍

 

[nze82]

"When solid NH4NO3 is dissolved in water at 25 degrees C, the solution temperature decreases. This reaction is endothermic."

Why is it true? I thought since the solution is losing heat, becoming colder, then it would be exothermic.

The actual reaction is the dissolving of NH3NO3. The solution is the system, in which the reaction is taking place. Since the reaction has absorbed heat from the system (causing the temperature of the system to drop), then it's endothermic.

 

[dl2501]

Not necessarily. You might see a reaction where they don't even mention the temperature of the surroundings. Something like..

A + B + 1050KJ ----> AB

You should be able to identify that this reaction is endothermic as it required an input of energy. If you notice that energy is going in, you should assume that the surroundings of the reaction are getting cooler as they are loosing energy (heat) to form that bond.

AB ----> A + B + 1050KJ

Now this reverse reaction on the other hand, is exothermic. You can see that energy is released. The release of energy would increase the temperature of the surroundings. Heat and energy, in most cases, are synonymous with each other.

Im sorry to bring up an old post, but for this reaction that you mention, bond formation is related to the release of energy. So wouldn't you expect A + B -> AB to be exothermic, and thus make the the surrounding hotter? Or does this imply the OVERALL reaction?

Thank you!