Effect on Enthelpy Changes By Using HNO3 Instead of HCl

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Discussion Overview

The discussion centers on the potential effects of using nitric acid (HNO3) instead of hydrochloric acid (HCl) in a reaction involving sodium hydroxide (NaOH) and its impact on measured enthalpy changes. The scope includes experimental considerations and reasoning behind the differences in enthalpy values.

Discussion Character

  • Exploratory, Homework-related, Technical explanation

Main Points Raised

  • One participant questions the effect of substituting HCl with HNO3 in the reaction, noting that some experimental values suggest a lower enthalpy change with nitric acid.
  • Another participant suggests considering the net ionic equation for both reactions, leading to a simplified reaction of hydroxide ions and hydrogen ions forming water.
  • A later reply indicates that while the net ionic equation appears similar, HNO3 is noted as the weakest of the strong acids, implying it may not be fully dissociated in solution, which could affect the enthalpy change.
  • This participant expresses uncertainty about the magnitude of the difference in enthalpy changes and the precision required for it to be measurable, suggesting that while a difference exists, it may be minor.

Areas of Agreement / Disagreement

Participants express differing views on whether there is a significant effect on enthalpy changes when using HNO3 instead of HCl, with some suggesting no effect and others indicating that a measurable difference may exist due to dissociation characteristics.

Contextual Notes

The discussion highlights the importance of considering acid dissociation in enthalpy calculations, but does not resolve how this impacts the overall measurements or the conditions under which differences may be observed.

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Homework Statement


What effect, if any, would using nitric acid instead of hydrochloric acid in the reaction

NaOH(s) + HCl(aq) --> NaCl(aq) + H2O(l)

have on the enthalpy changes measured in an experiment?


Homework Equations



N/A

The Attempt at a Solution



I have no idea. Some experimental values I found online suggest that using nitric acid would give a lower enthalpy change value? But I wish to know the reasoning behind this.
 
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Consider the net ionic equation for both reactions.
 
Um after doing that i got the net reaction of
OH-(aq) + H+(aq) --> H2O(l)
for both reactions...so does that mean there is no effect?
 
ff_yy said:
does that mean there is no effect?

Yes.

With one important comment. HNO3 is the weakest of the so called strong acids, thus it is not necesarilly 100% dissociated (1% not dissociated in 0.1M solution). Thus enthalpy of the reaction between HNO3 and NaOH has to take HNO3 dissociation into account. No idea how large the difference is and how precise the experiment has to be for the difference to be measurable, but it exists.

But that's close to nitpicking.

--
 

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