[NoRage]

Hello.

I have a question regarding ammonium nitrate. Why is the reaction endothermic when you apply ammonium nitrate with water? What makes it endothermic and not exothermic?

[opti384]

The reason why it's endothermic is that the reactants are stable than the products. Therefore, in order for the reaction to progress, you need energy since the reactants are stable.

[NoRage]

The reason why it's endothermic is that the reactants are stable than the products. Therefore, in order for the reaction to progress, you need energy since the reactants are stable.

Why are the reactants more stable than the products? Is there a way that a can take notice of this just by looking at the chemical compounds?

You're saying that you need energy in order for the reaction to progress (endothermic), does that mean that you do not need energy at all for the exothermic reaction?

Could you explain a bit more about the difference between these two reactions? (I do know that endothermic reaction takes energy and exothermic gives energy away.) If, in endothermic reactions, the reactants are more stable than the products, does this mean that in exothermic reactions reactants are less stable than the products? And yet again: is there a way a can quickly identify whether the reactants are more stable than the products and vice versa?

[rabolisk]

Indeed in exothermic reactions the reactants are less stable than the products. Exothermic reactions give off net energy (although not necessarily useful energy), but still require some input energy initially (activation energy). Combustion of gasoline is a very exothermic process, but still requires some input energy. An open source of gasoline does not spontaneously combust in air.

It is difficult to just look at a chemical reaction and determine the enthalpy change associated with the reaction. There are trends though. Combustion is exothermic, melting and boiling are endothermic, and freezing and condensation are exothermic (almost always). Enthalpy of dissolution for solids tend to be all over the place and it is tough to determine whether it is positive (endothermic) or negative (exothermic). Note that just because something is soluble (solubility rules) does not mean that it has an exothermic enthalpy of dissolution. Hope that helped.