please help thank u Experiment 9: This experiment explores Hess\' Law, a corners

Question

please help thank u

Experiment 9: This experiment explores Hess' Law, a cornerstone of thermochemistry. The enthalpy of reaction delta H for two acid-base reactions serves as key property to employ and confirm Hess' law. The two acid-base reactions utilize a strong add - HCI - as well as a weak acid - CH3COOH. The base used is solid sodium hydroxide. 1. The heat of neutralization of solid sodium hydroxide with an aqueous solution of an acid might be determined directly in a one-step reaction or indirectly using a two-step reaction. Explain the difference between a one-step and a two-step reaction mechanism when determining the heat of neutralization. 2. Would you expect different values for the heat of the neutralization reaction, when solid NaOH is neutralized with an aqueous solution of a weak acid or with an aqueous solution of a strong acid? Explain your answer. 3. Explain how the fact that the weak acid is only partially dissociated might cause discrepancies between a theoretical predicted and an experimentally determined value.

Explanation / Answer

1) one -step reaction NaOH (aq) + HCl (aq) --------------------> NaCl (aq) + H2O (l)

two-steps reaction:

NaOH (aq) -----------------------> Na+ (aq) + OH-(aq)

HCl(aq) -----------------------> H+ (aq) + Cl- (aq)

finally H+ (aq) + OH- (aq) --------------> H2O (l)

in both cases heat of neutralisalisation same. because acid H+ react with base OH- froms liquid water. it is the neutralisation . remaining ions are spectator ions.

so here net reaction between strong acid + strong base i.e H+ (aq) + OH- (aq) --------------> H2O (l)

always gives   -13.7 kcal / mol energy

2)

NaOH + strong acid -------------------> -13.7 kcal /mol

NaOH + weak acid ---------------------> < -13.7 kcal /mol

here heat of neutralisation value in second case lesser . it is due to one weak compound. when one weak acid/base react with strong acid /base . heat of neutralisation value decreases . the leser value is due weak compound utilise the heat to dissociation.

(3)

weak acid only partially dissociates due to this some amount of heat utilised by the weak acid for complete neutralisalisation reaction . that's why we laways get lesser heat in case of SB+ WA neutralisalisation reaction compared to SA+ SB

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