Why does the dissolution of NH4NO3 happen if the ∆H is 28.1?

[ScienceMonkey]

1. Why does the dissolution of NH4NO3 happen if the ∆H is 28.1? I'm supposed to be detailed with an equation, and explaining spontaneity.

Does it happen because of the energy created from protonation?

2. And why is only a strong base able to make H3PO4 act as an acid after the 3rd acid dissociation?

Is it because it is electronically unfavorable?

 

[GCT]

1) at constant temperature and pressure what concept relates to sponaneity (depends on both entropy and enthalpy of process).

2)In terms of a base, how strong is PO4^2- compared to H2PO4^-1? What is the Arrehnius concept of an acid base neutralization in perspective of the conjugate acid/bases?

 

[Blueshift5]

The dissolution of NH4NO3 occurs because the change in enthalpy (∆H) of the reaction is positive, meaning that energy is released when the compound is dissolved in water. This energy is used to break the bonds between the ammonium and nitrate ions, allowing them to separate and interact with the water molecules. This process is known as hydration, and it is driven by the favorable interactions between the ions and the polar water molecules.

The dissolution of NH4NO3 can be represented by the following equation:

NH4NO3 (s) → NH4+ (aq) + NO3- (aq)

This reaction is spontaneous because the change in Gibbs free energy (∆G) is negative, indicating that the system is becoming more stable. This is due to the favorable interactions between the ions and water molecules, which lead to an increase in entropy (∆S). In other words, the formation of the hydrated ions is more energetically favorable than the solid compound, making the dissolution process spontaneous.

Regarding the second question, the reason why only a strong base can make H3PO4 act as an acid after the third acid dissociation is because of the electronic structure of the phosphate ion. As the acid dissociates, it loses protons and becomes more negatively charged. This leads to increased repulsion between the negative charges, making it more difficult for another proton to be removed. A strong base, such as hydroxide (OH-), is able to overcome this repulsion and remove the third proton, making H3PO4 act as an acid again.

In addition, the third acid dissociation of H3PO4 is also electronically unfavorable because the phosphate ion is highly stabilized by resonance. This means that the negative charge can be delocalized over multiple atoms, making it less likely for a proton to be removed. A strong base is able to overcome this stability and remove the third proton, making H3PO4 act as an acid again.

Overall, the dissolution of NH4NO3 and the ability of a strong base to make H3PO4 act as an acid after the third dissociation are both driven by the favorable interactions between ions and water molecules and the electronic structures of the compounds involved.