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Science Forum Index » Chemistry Forum » Stability of cuprous oxide?...
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| Stig Holmquist... |
 Posted: Sun May 04, 2008 3:04 pm |
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In a compilationof metallurical phase diagrams I found one for the
system Cu-O. It shows Cu2O decomposing to Cu+CuO at 375 C.
But free energy of formation data for Cu2O is - 147 Kcal and for CuO
it is -130 Kcal. at 300K. So how can Cu2O be unstable below 375 C?
Stig Holmquist |
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| Ian Gay... |
| Posted: Sun May 04, 2008 8:12 pm |
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Stig Holmquist wrote:
Quote: In a compilationof metallurical phase diagrams I found one for the
system Cu-O. It shows Cu2O decomposing to Cu+CuO at 375 C.
But free energy of formation data for Cu2O is - 147 Kcal and for CuO
it is -130 Kcal. at 300K. So how can Cu2O be unstable below 375 C?
Stig Holmquist
Why would you think ΔG is independent of T?
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| Stig Holmquist... |
| Posted: Mon May 05, 2008 5:45 am |
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On Sun, 04 May 2008 18:12:21 -0700, Ian Gay <gay at (no spam) sfuu.ca> wrote:
Quote: Stig Holmquist wrote:
In a compilationof metallurical phase diagrams I found one for the
system Cu-O. It shows Cu2O decomposing to Cu+CuO at 375 C.
But free energy of formation data for Cu2O is - 147 Kcal and for CuO
it is -130 Kcal. at 300K. So how can Cu2O be unstable below 375 C?
Stig Holmquist
Why would you think ?G is independent of T?
I don't, and the difference gets larger as the temperature increases.
If you heat a powder compact of Cu + CuO in nitrogen at 425 you 'll
get redbrown Cu2O.
Stig |
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