Diamond and graphite

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Anjali_U_3L
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Joined: Wed Sep 21, 2016 2:57 pm

Diamond and graphite

Postby Anjali_U_3L » Mon Feb 20, 2017 5:40 pm

In the course reader, it says diamond is kinetically stable with respect to graphite. What does this mean?

Theresa Dinh 3F
Posts: 26
Joined: Fri Jul 22, 2016 3:00 am

Re: Diamond and graphite

Postby Theresa Dinh 3F » Mon Feb 20, 2017 9:30 pm

Calculating by kinetics (by k and stuff) provides an answer that is mostly stable for diamond, but the thermodynamic equations (gibbs free energy) show that it is unstable.

Chem_Mod
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Re: Diamond and graphite

Postby Chem_Mod » Mon Feb 20, 2017 9:39 pm

What this means is that, for diamond to convert back into graphite there is a large activation barrier. The delta H of formation for diamond is actually higher in energy (meaning the product is less stable) than it is for graphite. This means that graphite is more stable, but diamond will not convert back into it because it would require a tremendous amount of energy to overcome the energy barrier to do so.

Alex Yee - 4I
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Re: Diamond and graphite

Postby Alex Yee - 4I » Wed Feb 22, 2017 11:52 am

So if I isolate 50g of diamond at STP for 100 trillion years, will any of it form into graphite? I get that the activation energy effectively prevents it from undergoing the reaction (you won't see diamonds turn into graphite in your hands), but does this reaction have a ridiculously long half-life, or just never occur at STP?

Mary Becerra 2D
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Joined: Fri Sep 29, 2017 7:06 am

Re: Diamond and graphite

Postby Mary Becerra 2D » Thu Feb 22, 2018 2:46 pm

With that example he gave in lecture, he drew a diagram showing that while graphite is at lower and a more stable energy, the activation energy required to turn diamond into graphite is too large for it to spontaneously happen (at least at standard conditions).

Magdalena Palavecino 1A
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Joined: Fri Sep 29, 2017 7:04 am

Re: Diamond and graphite

Postby Magdalena Palavecino 1A » Thu Feb 22, 2018 3:40 pm

Diamond turns into graphite spontaneously, but that does not mean it occurs fast. In fact, it happens very very slowly, for kinetics rather than thermodynamics is controlling this reaction. The diamond is kinetically stable with respect to graphite, yet thermodynamically unstable.

Yu Chong 2H
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Joined: Fri Sep 29, 2017 7:05 am

Re: Diamond and graphite

Postby Yu Chong 2H » Fri Feb 23, 2018 3:28 pm

Kinetically stable just means that the reaction from diamond to graphite is too slow to be accounted for normally.

Miguel Velasco 2J
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Re: Diamond and graphite

Postby Miguel Velasco 2J » Sun Feb 25, 2018 10:40 pm

Delta H of formation for diamond is higher in energy than it is for graphite and happens at a much slower rate.

Ashley Garcia 2L
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Joined: Fri Sep 29, 2017 7:05 am

Re: Diamond and graphite

Postby Ashley Garcia 2L » Mon Feb 26, 2018 2:41 pm

The reaction of diamond --> graphite is spontaneous. Spontaneous does not imply that the reaction is fast, it means the reaction will eventually occur (because energy of the reactants > energy of the products).

Therefore, a diamond is kinetically stable with respect to graphite because there is a large activation energy barrier separating the reactant (diamond) from the product (graphite). This reaction would require a large amount of energy to overcome this barrier, so diamond will not likely convert to graphite.


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