J.R. S. answered • 09/21/17
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3Al(s) + 3NH4ClO4(s) --> Al2O3(s) + AlCl3(s) + 3NO(g) + 6H2O(g)
Enthalpy of reaction = ∑∆Hf(products) - ∆Hf(reactants)
[ΔHf(Al2O3(s) + ΔHf(AlCl3(s) + 3ΔHf(NO(g)) + 6ΔHf(H2O(g)] - [3ΔHf(Al(s)) + 3ΔHf(NH4ClO4(s)]
[∆Hf(H2O(g)] - [Hf (H2(g) + 1/2∆Hf(O2(g)
There simply isn't sufficient data provided to answer these questions. The "relevant" heats of formation do not include values for AlCl3(s), NO(g) and H2O(g). Values for Al(s), H2(g) and O2(g) are zero so do not need to be provided. Thus, IMHO (1) cannot be answered.
No information as to mass of each reactant is provided, therefore (2) cannot be answered. However, one could use the mole ratio to get this answer
Not sure what they want for (3).
J.R. S.
tutor
Hess' Law is fine, but you still need the various chemical equations and ?H for each of those equations in order to use Hess' Law. Recall that Hess' Law pretty much states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes. But the fact remains that to go from A --> B, if using Hess' Law, you still need to know the composite reactions that allow you to compute ?H for the target reaction. Unless I'm missing something, there just isn't enough info provided, even to use Hess' Law. If you just use what's given, you get -700 kJ/mol - (-290 kJ/mol) = - 410 kJ/mole for the first rx. For the second, look up ?Hf H2O(g) and that will be ?Hf for second rx.
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09/22/17
Jessie T.
i see you said that heat of formation was not given for AlCl3 but the heat of formation for AlCl3 is -700, and when its asking for the energy released for each fuels, the two fuels are Al2O3 and AlCl3
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09/22/17
J.R. S.
tutor
My bad about the ?Hf for AlCl3, but I'm sorry, I still can't see how you can use Hess' Law unless you are suppled with additional reaction equations and associated ?Hf's. For example, if the target reaction is A ==> B, and you know the ?H for
A==>C and for C==>B, then you can use Hess' Law to find ?H for A==>B.
I wish I could be of more assistance, but I must be missing something, because I still don't see how one can use Hess' Law without additional information. Also, what about the second reaction? You aren't asking about ?H for H2(g) + 1/2 O2(g) → H2O(g)? If, and when you ever get the solution to this problem, I'd like you to share it with me, because I've been doing these types of problems for many years and just don't see how you can evaluate the energy of the overall reactions from the supplied data.
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09/22/17
Jessie T.
yeah this question is just everywhere for me which is why im struggling with it, but thank you for the attempt! if i find the answer ill be sure to post it
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09/22/17
J.R. S.
tutor
Thanks. Please message me directly if you get the answer otherwise I may miss it. Good luck.
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09/22/17
Jessie T.
09/22/17