Dissolving of ammonium-nitrate in water is endotermic reaction.
The formula for entropy is :delta: S= :delta: Q/T.
If a reaction is endotermic that means that :delta:H>0(positive)
Conditions are ideal and temperature is const. So the change of entropy is positive. =D
If u don't get smth just say
That's not right. First, :delta: S = :delta: Q/T is not correct. There is no such thing as :delta: Q. Besides, you're implying that ALL endothermic reactions necessarily result in increase in entropy of the system (positive :delta: S), which is also not right.
The reason :delta: S is positive comes from :delta: G = :delta: H - T :delta: S. You had to know that solvation of ammonium nitrate in water was a spotaneous reaction. But whenever something is said to dissolve in water, the reason it dissolves is because it is spontaneous (The fact that a reaction occurs, by definition, must mean that the reaction is spontaneous). With :delta: H being positive, :delta: S had to be positive for the reaction to occur.