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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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EA EA
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10 years ago
Show and/or explain your work in determining the change in enthalpy for the production of the hot chemical spray described above. (4 marks) info is in the diagrams
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Doctor-2-BDoctor-2-B
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Pretty fly for a SciGuy

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EA Author
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#2
10 years ago
Quote from: Doctor-2-B (10 years ago)
These changes are made according to Hess' Law:

Change equation I to:
2 H2O2(aq) -> 2 H2O(l) + O2(g)

This changes the enthalpy (ΔH) to -189.2 kJ.

Now, take 1/2 of each in equation 1:
H2O2(aq) -> H2O(l) + ½O2(g)

This halves the enthalpy to -94.6 kJ.

Change equation II to:
H2(g) + ½O2(g) -> H2O(l)

This changes the enthalpy to -285.8 kJ.

Leave equation III as is.

H2O2(aq) -> H2O(l) + ½O2(g)
H2(g) + ½O2(g) -> H2O(l)
C6H4(OH)2(aq) -> C6H4O2(aq) + H2(g)

The sum of these three reactions is:
H2O2(aq) + H2(g) + ½O2(g) + C6H4(OH)2(aq) -> H2O(l) + ½O2(g) + H2O(l) + C6H4O2(aq) + H2(g)

Cancelling species on both sides of the and summing the 2 water molecules on the right side of the ->:
C6H4(OH)2(aq) + H2O2(aq) -> C6H4O2(aq) + 2 H2O(l)

We can now simply sum the enthalpies: -94.6 kJ + -285.8 kJ + 177.0 kJ = -203.4 kJ
This indicates that the reaction is exothermic (it releases heat).
thank you Slight Smile
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10 years ago
My pleasure.  I hope it was explained verbosely enough to understand.
Pretty fly for a SciGuy
EA Author
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#4
10 years ago
Quote from: Doctor-2-B (10 years ago)
My pleasure.  I hope it was explained verbosely enough to understand.
yes it was ! definitely
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