Carbon as graphite  [ENDORSED]

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Christina Cen 2J
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Carbon as graphite

Postby Christina Cen 2J » Sun Jan 21, 2018 10:08 pm

Can someone explain to me again why carbon is more stable as graphite and why in 67 b, it isn't a gas like hydrogen and oxygen?

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Re: Carbon as graphite

Postby Ashin_Jose_1H » Sun Jan 21, 2018 10:17 pm

In 67b, C(gr) means that we are looking at Carbon in graphite form. I'm not too sure on why Carbon is more stable as graphite.

Xihui Yin 1I
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Re: Carbon as graphite

Postby Xihui Yin 1I » Sun Jan 21, 2018 10:48 pm

In the graphite form, carbon is sp2 bonded to 3 other carbon atoms to form a hexagonal ring. However, each C still has a spare 2p orbital containing an electron. The 2p orbitals overlap to form a delocalised pi bonding system and as such, rings of carbons exist as individual sheets. Dispersion forces exist between these sheets and results in stability.

Pooja Nair 1C
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Re: Carbon as graphite

Postby Pooja Nair 1C » Thu Jan 25, 2018 6:57 pm

Because you are finding the standard enthalpy, you have to use the elements in their most stable state. For hydrogen and oxygen, the most stable form is in H2 and O2 gas, but for carbon, the most stable state is as graphite.

Jana Sun 1I
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Re: Carbon as graphite

Postby Jana Sun 1I » Fri Jan 26, 2018 2:16 pm

This might be going on a limb, but I thought carbon's most stable form was as diamond. Can someone explain why/how graphite is most stable than diamond?

Abel Thomas 2C
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Re: Carbon as graphite

Postby Abel Thomas 2C » Fri Jan 26, 2018 2:31 pm

In graphite, carbon is sp2 hybridized and possesses free electrons which are delocalized. In diamond, carbon is sp3 hybridized and there are no free electrons. Delocalization is what makes graphite more stable than diamond, since there are more van der waals interactions.

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Re: Carbon as graphite  [ENDORSED]

Postby Chem_Mod » Mon Jan 29, 2018 2:00 pm

To expand on what other students have been saying, graphite exists as layers of graphene sheets. These sheets, like previously described, consist of sp
hybridized carbons, essentially like a bunch of benzenes all chained together in a continuous sheet. This delocalizes electrons, making it a stable structure. Additionally, the sheets undergo stacking, which consists of interactions between the positive center of the rings and the negative exterior, which further stabilizes the structure. Diamond is actually less stable and degrades over time back to graphite, so saying that diamonds are forever is technically untrue.

Hellen Truong 2J
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Re: Carbon as graphite

Postby Hellen Truong 2J » Mon Feb 12, 2018 12:57 am

When using C(gr) to solve for reaction enthalpies using the bond enthalpy method, why would you add the atomization or sublimation of carbon (+717kj/mol)?

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