a neutralization reaction occurs when 120ml of 1.00mol/l lioh and 160nl of 0.75 mol/l hno3 are mixed in an insulated cup. initially, the solutiona are at the same temperature. If the highest temp during mixing was 24.5C, what was the iniyial temp of the solutions? The density is 1.00g/ml and the specific heat capacity is 4.19J/gC.

Question

anonymous · Answer

Vt=280mL
m=280g
$$DeltaH=-53.1kJ$$
n=0.12mol

Ti=(Q/mc)  -Tf

This is all I got so far.

anonymous · Answer

LiOH+HNO3-------> LiNO3 + H2O+ 53.1kJ

rogue · Answer

Is that the whole question? It seems a bit vague. :(
How did you get the delta H by the way?

anonymous · Answer

Yeah that is the question.
This equation was given LiOH+HNO3-------> LiNO3 + H2O+ 53.1kJ.

rogue · Answer

Oh, okay, how about the mass 280 g?

anonymous · Answer

so i calculated the total volume and then i used the density formula to find the  total mass.

rogue · Answer

Hmm, I feel like the problem is a bit more complicated than this, but why don't you just try substituting what you?$$T _{i}^{} = \frac {Q}{mc} - T _{f}^{} = \frac {-53 kJ}{280 g * 0.00419 J/gC} - 24.5 C$$

rogue · Answer

What you have*

rogue · Answer

0.00419 kJ/gC*

anonymous · Answer

my teach told me to use deltaHr =deltaH/n

anonymous · Answer

so I first found the n=mv=1.00mol/L * 0.12L=0.12mol

rogue · Answer

Ah, right, 53.0 kJ of energy is released for every 1 mole of LiNO3 formed. So the actual delta H for the sample given would be 53.0 kJ/mol * 0.12 mol = 6.36 kJ

anonymous · Answer

but it is in kJ not kJ/mol :S I'm confused.

rogue · Answer

Well, according to the reaction, when 1 mole is formed when 53.0 kJ is released. So the delta H rxn = 53.0 kJ/mol.

rogue · Answer

Hmm, am I explaining that or just repeating? Don't really know how to say it...

anonymous · Answer

Oh okay, now it makes sense :) Thank you soooo much. Let me calculate the final answer and show it to you.

anonymous · Answer

i got -19.1C

rogue · Answer

The Q should be negative right?

anonymous · Answer

I would guess so, since energy is released. right? then the answer would be -29.9

rogue · Answer

I really don't like this question :(
It'd be great if someone else could also do this question to verify the answer.