Question

Thermodynamically, in which form of carbon is the most stable?

• A. Coal
• B. Fullerenes
• C. Diamond
• D. Graphite

Hint:

The standard enthalpy of formation of graphite is defined as zero, while diamond has a positive value, confirming its lower stability.

Answer 1

The Correct Option is D

To determine which form of carbon is the most thermodynamically stable, we need to consider the enthalpy and free energy aspects of different carbon allotropes.

Concept Explanation:

• Coal is an amorphous form of carbon that contains a variety of impurities and is not a pure allotrope. It is primarily used as a fuel.
• Fullerenes are a form of carbon that consists of carbon atoms arranged in a spheroidal closed cage, like molecules of C₆₀ (Buckminsterfullerene), but they are not the most stable form due to their higher energy configuration.
• Diamond is a crystalline form of carbon with a lattice structure, known for its remarkable hardness but is not the most stable thermodynamically.
• Graphite is a crystalline form of carbon with hexagonally arranged carbon atoms in layers. This arrangement gives the atoms more freedom to move, leading to greater stability.

Graphite is the most stable form of carbon under standard conditions. This statement is backed by its lower enthalpy compared to other carbon allotropes. This stability is due to the strong covalent bonds within the layers and the ability for the layers to move relative to each other, which allows for energy minimization.

Additionally, thermodynamic data indicate that the standard enthalpy of formation for graphite is zero, making it the reference state for carbon. This implies that graphite is the most stable form of carbon at room temperature and pressure.

Conclusion: The correct and thermodynamically most stable form of carbon is Graphite.