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Super hard chem question?
Im going to keep posting these until one of you guys answers SOMETHING so i can figure out who the heck to do it <3 Basically, it's a really hard multiple part question and i have NO idea what i'm doing. So if you can solve any of the parts and show your work, that would be great! If you could do it all, that we be even better! But im really looking for an explanation as well because I have a lot of these problems to do, thank you!
for the things you might not be able to read:
240cm^3 is the first thing on the page
100cm^3 is the next number
33.5 degrees C is after that
(specific is the next word
24.0dm^3 at r.t.p. is that last line
1 Answer
- Steve OLv 78 years agoFavorite Answer
240cm^3 of ethane at 24.0 dm3 per mole,
A) find moles of ethane:
(0.240dm^3) / (24.0 dm3 per mole) = 0.0100 moles of ethane
===========
B) find dH reaction, which heated up 100 cm3 of water, at 1g/ml = 100 grams of water
p.s. a dT of +33.5 Celsius, raises the kelvin temp by 33.5K as well
dH reaction = - dH water
dH reaction = - (mass H2O) (spec ht H2O) (dT)
dH reaction = - (100 grams) (4.18 J/g-K) (33.5 K)
dH reaction = -14,003 Joules
which rounded to 3 sig figs, & converted into kJ is
dH reaction = -14.0 kiloJoules
===============================
C) find kJ per mole ethane combustion:
(-14.0 kiloJoules) / (0.0100 moles rethane) = dH reaction = - 1,400 kj/mol
=====================
D) use dHf's to find dH reaction for the combustion of 1 mole of C2H6:
1 mole C2H6 & 3.5 O2 --> 2 CO2 & 3 H2O
dHreaction = (dHf products) - dHf reactants)
dHreaction = [(2)(dHf CO2) & (3)(dHf H2O)] - [(dHf C2H6) & (3.5)(dHf O2)]
dHreaction = [(2)(-394kJ) & (3)(-286 kJ)] - [ -85) & (3.5)(zero)]
dHreaction = [(-788) & (-858)] - (-85)
dHreaction = -1646 + 85
dH = -1561kJ/mol
========================
E) possible dicrepancy
not as much heat was lost to the water, 14,00 kJ, as should have been ... 1561 kJ
likely heat was lost to other materials in the surroundings other than water:
to the thermometer, to the container, to the air ...
also it is also dependent upon how thw dT was measured, dT is not accurate uless the final T is accurate. often times people take the highest temp recorded as the final temp.
In actuality the final temp should be higher, because it begins to cool off, as soon as the temp begins to rise.