Endothermic Reactions

[BenZq]

How is this possible?

Adding NH4NO3(s) to water lowers its temperature. How can this be explained?

A.The solvation energy is greater than the lattice energy.
B.The solvation energy is less than the lattice energy.
B is the best answer. If the water became cooler after the ammonium nitrate was added, the reaction must have been endothermic and was driven by the increase in entropy associated with dissolving salt into water. An endothermic reaction means that the bonds broken during the reaction are of higher energy than the bonds formed, which in turn means that the lattice energy (from the bonds broken) is higher than the solvation energy (from the bonds formed). The best answer is B.

The explanation seems to be wrong, or maybe I don't understand this fully. Can anyone Help?

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[TieuBachHo]

Well, here is what I think it means.

This rxn is endothermic b/c it requires energy from solvent (H2O) to dissolve the salt (NH4NO3(s)) and thus the solution became cooler afterward. Usually we think of an endothermic rxn is when a rxn gains outside/input heat. But the heat energy can also transfer from within its own rxn. Therefore, this rxn requires more energy to break up a bond (lattice energy of NH4NO3) to form a lesser bond with water (solvation energy of salt water). You may ask, then where does the energy goes? It increases the entropy of water salt mixture.

 

[ilovemcat]

Where'd you get this from if you don't mind me asking?

 

[BenZq]

Well, here is what I think it means.

This rxn is endothermic b/c it requires energy from solvent (H2O) to dissolve the salt (NH4NO3(s)) and thus the solution became cooler afterward. Usually we think of an endothermic rxn is when a rxn gains outside/input heat. But the heat energy can also transfer from within its own rxn. Therefore, this rxn requires more energy to break up a bond (lattice energy of NH4NO3) to form a lesser bond with water (solvation energy of salt water). You may ask, then where does the energy goes? It increases the entropy of water salt mixture.

Thanks, that makes sense. I don't know what I was thinking when I posted this, but now it all seems so clear lol.