Question

Rxn #1: NaOH(s) ® NaOH(aq)

Rxn #2:     NaOH (s) + HCl (aq) ® H₂O (l) + NaCl (aq)

Rxn #3:    NaOH (aq) + HCl (aq) ®H₂O (l) + NaCl (aq)

1. what's happening at a molecular level for EACH of these reactions?

2. How are the three reactions related to each other? Explain. (Note: this question is not asking about the enthalpies for these reactions but only the chemical reactions (reactants and products) themselves

Answer 1

1.

In reaction #1, solid NaOH dissolves in water. Crystal lattice of solid NaOH breaks. Each NaOH molecule is surrounded by several water molecules.

In reaction #2, solid NaOH is neutralised with aqueous HCl to form salt (NaCl) and water.

In reaction #3 aqueous NaOH is neutralised with aqueous HCl to form salt (NaCl) and water.

Note: NaOH is base and HCl is acid. The reactions 2 and 3 are acid - base neutralisation reactions. The only difference between reactions 2 nd 3 is the physical state of NaOH.

2.

If we add reactions #1 and #3, we get reaction #2. In other words, the overall reaction #2 is represented by stepwise reactions #1 and #3. Thus, neutralisation of solid NaOH is represeted by dissolution of solid NaOH in aqueous medium and the neutralisation of aqueous NaOH.