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Topic: HESS CYCLE  (Read 2289 times)

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Offline heartOFscience

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« on: January 04, 2012, 04:25:21 PM »
Hi please open the picture I've attached. It Contains a worked example to a question about calculating the enthalpy change of liquid water to gas water.

now I understand the Hess cycle and I can find enthalpy of formation and combustion, but for some reason I am really really lost with their example.

I don't understand why when the question is asking for 1 mole of H2O, they have done 2H2O.

Please help me, I've been trying to figure out what's going on for a while now, and I've got nothing, if someone could try and explain each step, so the understanding and concept is clear in my mind, then it would be very much appreciated!!!!!

Offline UG

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« Reply #1 on: January 05, 2012, 01:58:48 AM »
In the final answer it has 2ΔH so they have taken the 2 moles of water into account. I think they have made it 2 moles so that you are calculating the bond enthalpy change for the reaction 2H2 + O2  :rarrow: 2H2O instead of H2 + 0.5 O2  :rarrow: H2O. Please get back if anything is still not clear.

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