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Topic: enthalpy diagrams  (Read 10458 times)

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Offline dg2008

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enthalpy diagrams
« on: May 27, 2009, 07:00:55 AM »


So I understand the first diagram but don't get the second one.

CH4(g) + 2O2(g)   -    CO2(g) + 2H2O(l)
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Offline Borek

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Re: enthalpy diagrams
« Reply #1 on: May 27, 2009, 08:05:13 AM »
Hard to help not knowing what you don't understand. I can't see a difference between both cases (well - plenty of differences, but the same ideas behind).
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Offline dg2008

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Re: enthalpy diagrams
« Reply #2 on: May 27, 2009, 08:36:56 AM »
how is the second one worked out from the equation?
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Offline Borek

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Re: enthalpy diagrams
« Reply #3 on: May 27, 2009, 08:55:04 AM »
Exactly the same way first one is.

Sorry, no idea where is the problem.
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Offline dg2008

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Re: enthalpy diagrams
« Reply #4 on: May 27, 2009, 08:59:12 AM »
Wheres the 1/2H + 1/2H -> HI in the equation, thats what I don't get, the first one is reactants at top & products at bottom. I just don't understand where the other stuffs coming from
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Offline Borek

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Re: enthalpy diagrams
« Reply #5 on: May 27, 2009, 09:15:31 AM »
No, it is reactants on the left, products on the right. Read axes labels.
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Offline dg2008

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Re: enthalpy diagrams
« Reply #6 on: May 27, 2009, 09:23:01 AM »
yes I know they change depending on exothermic, endothermic etc I get that bit.

Products have less stored energy than the reactants (exothermic) or more than the reactants (endothermic).

Is the second diagram not from the same equation?
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Offline Borek

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Re: enthalpy diagrams
« Reply #7 on: May 27, 2009, 09:44:33 AM »
Quote from: dg2008 on May 27, 2009, 09:23:01 AM
Is the second diagram not from the same equation?

Geez, what equation?

First diagram is for the methane combustion, second diagram is for HI synthesis. You have already listed both reaction equations.
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Offline Anenin

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Re: enthalpy diagrams
« Reply #8 on: June 03, 2009, 09:22:36 AM »
Quote from: dg2008 on May 27, 2009, 07:00:55 AM


So I understand the first diagram but don't get the second one.

CH4(g) + 2O2(g)   -    CO2(g) + 2H2O(l)

first one is exothermic because the enthalpy is negative..
second one is endothermic because the enthalpy is positive..
(H2 + I2 = 2HI)

The site from which you have taken the image has another image further below with more detailed info about reaction enthalpies...
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