[mehmetco]

So in the case of

1. MgSo4 in H20 the solution formation = -91 kj/mol (exothermic)

2. NH4NO3 in H20 the solution formation = +26 kj/mol (endothermic)

According to my professor both are solutions. Now what i don't understand is, how can I be able to tell if both not only one is a solution. Because I know that exothermic reactions tend to be solutions. But in the case of a endothermic solution, how is this possible?

I know it has something to do with entropy and enthalpy. But lets on an exam, how will I be able to tell?

[mehmetco]

Hi Guys,

Sorry for all of the posts, but, so a supersaturated solution is thermodynamically unstable solution. But, why would precipitation occur rapidly if a nucleating material is added?

[Borek]

Please elaborate on what you don't understand - this question can be addressed from many, many sides.

[Borek]

I know that exothermic reactions tend to be solutions.

Reaction is not a solution. What you probably mean is that "exothermic reactions tend to produce solutions" - which is a bit better, but still wrong, as carbon burning is exothermic, but doesn't produce solution. What about "substances that dissolve exothermically tend to be easily soluble"?

I know it has something to do with entropy and enthalpy. But lets on an exam, how will I be able to tell?

ΔG=ΔH-TΔS

(google for Gibbs energy).

[Enthalpy]

[...] I know that exothermic reactions tend to be solutions. But in the case of a endothermic solution, how is this possible?[...]

The ambient heat provides the necessary energy if the amount isn't too much. This happens during dissolutions and also for other operations. How much of the solid can dissolve depends on the missing enthalpy, the temperature, and other factors; the proper way to combine them and to compute is Gibb's energy G.