#1
2MnO4- + 10Br- + 16H+ ----> 2MN2+ + 5Br2 +8H20


100 mL of 2.00mol/L KmnO4 solution, 100.0mL of 2.00mol/L NaBr solution, and 300.0mL of 6.0 mol/L HCl solution are mixed and allowed to react. If the initial temperatures of all three solutions is 20.0 degrees C, and the temperature of the resulting solution is 24.7C, when the reaction is complete, estimate the enthalpy change for the above reaction as written. State any simplifying assumptions you must take. Look up any data you may need.


Ok im not really sure what to do here, do I use Qsystem + Qsurroundings = 0?

What "simplifying assumptions" do I need to make?
#2
uhhhggg, im doing the same thing, priciples of chem 2????
give me a sec and i'll figure it out
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#3
ugh we just started balancing chemical equations with solutions. my brain still hurts.
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#4
Formula is Energy/Enthalphy change=Mass times Specific heat capacity of water times temperature defect.

I would get on workin it out for u but I really cant b arsed.

Clue, take the mass of the solutions as the mass of the total amount of water. The assumption is water makes the mass of the solution as any ions have negligable mass.

EDIT: See my sig, use the thread there for any help regarding science. We wont give answers but we explain so you can do it yourself.
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Last edited by Guitardude19 at Feb 5, 2007,
#5
wow this is way too long for me to comprehend.
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#6
I think I did it right, I used nDeltaH + mcDeltat = 0

found the limiting reagent first, and assumed that the heat capacity was the same for that of water.

does that sound right?
Last edited by huk at Feb 5, 2007,
#7
E=MCdeltaT

E=0.6x4180x4.7

E= 11787.6kJ

Thats the energy change (enthalpy change) I got.

Assumptions I made:

The volumes of the reagents are mostly water therefore the total volume (600ml) was 0.6kg which is the same as the mass of water (density stays constant at 1g cm-3) in the reaction mixture.
Sat in a lab, curing diseases. They actually LET me play with chemicals!
#8
How did you get a mass of 0.6, shouldnt it be 500? Also, you cant just just that one simple equation, you have to factor in the molarity and find the limiting reagents.
#9
Quote by huk
How did you get a mass of 0.6, shouldnt it be 500? Also, you cant just just that one simple equation, you have to factor in the molarity and find the limiting reagents.


Yes its 0.5kg (500 grams) soz.

It says "as written" so you assume that the reaction has gone to completion and you will have measured the temperature change for a completed reaction. This gets rid of the need to factor in molarity.

It might be sleep depravation but I dont see a limiting reagent there.

EDIT: Been a long time since I last done one of these questions... Bout 3 yrs now lol.
Sat in a lab, curing diseases. They actually LET me play with chemicals!
Last edited by Guitardude19 at Feb 5, 2007,
#10
You definitely have to use the molarity values, or they wouldnt have given them.

You need the limiting reagent for use in the ndeltaH.
#11
Quote by huk
You definitely have to use the molarity values, or they wouldnt have given them.

You need the limiting reagent for use in the ndeltaH.


If your sure I wont argue, admittedly I havent done this in a while so you are confusing me lol. Maybe see your teacher (and pm me what he says.. I dont like not being able to do things that I once could).
Sat in a lab, curing diseases. They actually LET me play with chemicals!
#12
yeah i just had a test on this stuff... got a 60... sorry chemistry isn't meant to be understood wish i could help
#13
PV=nRT ??? that's all i got but i don't think it fits this equation
#14
Quote by coheed356
PV=nRT ??? that's all i got but i don't think it fits this equation


Thats a gas law lol. Doesnt work for this.
Sat in a lab, curing diseases. They actually LET me play with chemicals!
#15
Is this 11/12 chem? Jeez. I need to take either physics or chemistry for what I want to get into. I'm starting to think Physics.
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#16
Its chemistry 1011, the second intro chem course at my university.
#17
Quote by huk
Its chemistry 1011, the second intro chem course at my university.


.............Shamefully Im at univeristy doing chemistry. I should know that lol... Im sure Im right but then again I havent slept in 24 hrs and I havent touched that stuff in 3 years... So I could be very wrong. Sorry I couldnt be of better help.
Sat in a lab, curing diseases. They actually LET me play with chemicals!
#18
Yeah you are probably right. I did the first intro chem course 3 years ago, so that kind of screws me since I forgot EVERYTHING.


How about another?


Write formation equations for NaHSO4(s) and (NH4)2Cr2O7(s)
Last edited by huk at Feb 5, 2007,