Question

Which allotropic form of carbon is thermodynamically the most stable?
a.) Diamond
b.) Graphite
c.) Fullerenes
d.) Coal

Answer 1

Hint: Allotropes are structurally different forms of the same element. Carbon has many allotropes due to its valency. Thermodynamic stability is achieved by a closely packed and stable structure.

Complete step by step answer:
Let us solve this question by discussing the allotropes of carbon. Allotropes are those compounds which form different structures of the same elements. Carbon has many allotropes due to its valency. Carbon has a capability of having variable oxidation states or coordination numbers which makes carbon one of the few elements to have multiple numbers of allotropic forms. Another factor contributing to allotropes of carbon is its ability to catenate.
Let us look at the given options and discuss them one by one.
Diamond – It has a number of carbons which are linked together tetrahedrally. It is the hardest allotrope of carbon but not so thermodynamically stable.
Graphite – It has a layered structure, in which each layer has a hexagonal structure (called graphene). The layers are bonded by loose Vander Waal forces. It contains one delocalized electron per carbon, which leads to greater attraction between carbon atoms hence giving stronger bonds and more stability to the structure. Therefore, it is most stable, thermodynamically. It has zero standard entropy.
Fullerenes – They are prepared by evaporating graphene with laser, and they are soluble in organic solvents. They are not as stable thermodynamically.
Coal –is a combustible black or brownish-black sedimentary rock, formed as rock strata. It is made from carbon along with other elements such as hydrogen, sulfur, oxygen, and nitrogen.
Therefore, the answer is – option (b) – Graphite is the allotropic form of carbon which is thermodynamically the most stable.

Note: Graphite, because of its loosely intact carbon atoms or free electrons, it can easily move around from one place to another. Therefore, graphite is a good conductor of electricity.