Question

Thermodynamically most stable form of carbon is:
A. graphite
B. diamond
C. lonsdaleite
D. chaoite

Answer 1

Under normal and standard conditions, all carbon allotropes are solids. Thermodynamic stability will determine whether a given reaction and substance could be spontaneous and when a system is in its lowest energy state. The reactions which do not require energy to occur are called thermodynamically favoured reactions.

Complete step by step answer:
Let us discuss the options one-by-one to find the stable form of carbon:
A. graphite: It is the crystalline form of pure carbon. At standard temperature and pressure conditions, graphite is the most thermodynamically stable form of carbon. This is because they are chemically inert or resistant and require high temperature to react with oxygen.
B. diamond: Diamond is solid form and allotrope of carbon in which carbon atoms are arranged in cubic crystal form. In diamond, its basic element carbon, atoms are arranged in tetrahedral structure. In this structure, each atom is bonded to four nearest neighbours. Due to its structure, it's highly rigid and incompressible.
C. lonsdaleite: It is also an allotrope of carbon. It is also known as hexagonal diamond. This is because it has a hexagonal lattice. It contains interlocking rings of six carbon atoms. Its crystals are gray in colour. It does not occur naturally, it was synthesized in the labs by heating and compressing graphite in a static press. It resembles diamond and its properties.
D. chaoite: It is also an allotrope of carbon and known as white carbon. It belongs to the hexagonal crystal family also. It is a little harder than graphite. Its colour is black. The structure of the compound is almost similar to that of carbyne structure because of its electron diffraction pattern.

Thermodynamically the most stable form of carbon is graphite, which is option ‘a’.

Additional Information: Uses of graphite:
(1) Graphite is extensively used in the electrical industry to manufacture carbon electrodes and brushes in dry cell batteries.
(2) It is used in nuclear reactors. This is because graphite can absorb neutrons, so to stabilise nuclear reactions, graphite is used.

Note: The differences in stability, although both diamond and graphite have many significant physical differences, are same in many chemical properties which more involve the fact that they are composed of the same element than their macrostructure and other conditions that gave birth to their physical differences.