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Diamond and graphite

Posted: Mon Feb 20, 2017 5:40 pm
by Anjali_U_3L
In the course reader, it says diamond is kinetically stable with respect to graphite. What does this mean?

Re: Diamond and graphite

Posted: Mon Feb 20, 2017 9:30 pm
by Theresa Dinh 3F
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.

Re: Diamond and graphite

Posted: Mon Feb 20, 2017 9:39 pm
by Chem_Mod
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.

Re: Diamond and graphite

Posted: Wed Feb 22, 2017 11:52 am
by Alex Yee - 4I
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?

Re: Diamond and graphite

Posted: Thu Feb 22, 2018 2:46 pm
by Mary Becerra 2D
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).

Re: Diamond and graphite

Posted: Thu Feb 22, 2018 3:40 pm
by Magdalena Palavecino 1A
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.

Re: Diamond and graphite

Posted: Fri Feb 23, 2018 3:28 pm
by Yu Chong 2H
Kinetically stable just means that the reaction from diamond to graphite is too slow to be accounted for normally.

Re: Diamond and graphite

Posted: Sun Feb 25, 2018 10:40 pm
by Miguel Velasco 2J
Delta H of formation for diamond is higher in energy than it is for graphite and happens at a much slower rate.

Re: Diamond and graphite

Posted: Mon Feb 26, 2018 2:41 pm
by Ashley Garcia 2L
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.