[Johnboe]

Hi, here is a basic summary of what we did in a lab; there were 3 reactions:

The procedure:
Reaction 1: Solid sodium hydroxide dissolves in water to form an aqueous solution of ions.
NaOH(s)-> Na+(aq) + OH-(aq)     ΔH₁=-34.121kJ

Reaction 2: Solid sodium hydroxide reacts with an aqueous solution of HCl to form water and an aqueous solution of sodium chloride.
NaOH(s) + H+(aq) + Cl-(aq) -> H₂O + Na+(aq) + Cl-(aq) ΔH₂=-83.602kJ

Reaction 3: An aqueous solution of sodium hydroxide reacts with an aqueous solution of HCl to form water an an aqueous solution of sodium chloride.
H+(aq) + OH-(aq) + Na+(aq) + Cl-(aq) -> H₂O + Na+(aq) + Cl-(aq)  ΔH₃= -50.2kJ

The ΔH values were calculated by dividing the heat gained by the number of moles (each reaction had 0.05moles of NaOH)

The problem:

Net ionic equations for reaction 2 & 3:

2: NaOH(s) + H+(aq) -> H₂O + Na+(aq)
3: H+(aq) + OH-(aq) -> H₂O

i) In reaction 1, ΔH₁ represents the heat evolved as solid NaOH dissolves. Look at the net ionic equations for reactions 2 and 3 and make similar statements as to what ΔH₂ and ΔH₃ represent.

ii) Compare ΔH₂ with (ΔH₁ + ΔH₃). Explain in sentences the similarity between these two values by using your answer to #5 above.

Attempt at answering:
i) Firstly, ΔH₂ represents the heat evolved as the hydrogen ion displaces the sodium ion, creating a single displacement reaction. ΔH₃ represents the heat evolved as the hydrogen and hydroxide ion form water via a neutralization reaction.

ii) ΔH₂ is equal to (or supposed to be, this is a source of error while calculating) (ΔH₁ + ΔH₃). The similarity between these two values is that .. (this is where I get confused!)