basic neutralisation reactions

[Sarahisme]

we were asked to think about this question in our class today, and i am not entirely sure the answer

 

its to do with enthalphy heat of reactino stuff

 

The question was something like

 

why in the pracs we did involing the neutralisation acedic acid and HCL, was the change in temperature of the HCL greater?

 

my theory, and the keyword here is theory (or mroe correctly wild assumption ) is that.....

 

that stronger acids dissociate more (i have no real basis for this claim, just remember hearing it somewhere), and so there are more breaking of bonds, thus there must be a greater release of energy, resultingn in the greater increase of Temp. in the HCL neutralisation reaction. (i.e. because HCL is a stronger acid than the acedic acid)

 

well anyway, help or advice would be greatly welcommed

 

Sarah

[The Thing]

Yes your theory is actually correct. Good guesswork if that's what you say it is.

Anyways, strong acids ionize completely in an aqueous solution, and the neutralization reaction's net ionic equation will equal H⁺ + OH^- -> H₂O, with Δ[math]H^0=-57.3 kJ mol^-1[/math].

However, if a weak alkali or acid, or both, is/are used, then the enthalpy of neutralization will be lower than -57.3 kJ/mol, due to the fact, like you said, that weak acids ionize partially or very little in aqueous solutions, AND energy is ABSORBED trying to ionize the unionized molecules. This is what happens with acetic acid. It so happens that the neutralization of acetic acid with ammonia:

CH₃COOH(aq)+NH₃(aq)-> CH₃COONH₄

gives Δ[math]H^0 = -32.0 kJ mol^-1[/math]

[Sarahisme]

thanks for that

 

lol and i like your sig.

 

" Your problem is my problem, unless I have a problem with your problem, in which case we have a problem."

 

haha thats cool