Question

\(\Delta / I\) for the transition of carbon in the diamond form to carbon in the graphite form is \(-453.5 \mathrm{cal}\). This suggests that (1) Graphite is chemically different from diamond. (2) Graphite is as stable as diamond. (3) Graphite is more stable than diamond. (4) Diamond is more stable than graphite.

Short answer

Graphite is more stable than diamond (Option 3).

Step-by-step solution

Understanding the Problem

We need to determine the relative stability between graphite and diamond based on the given \(\frac{\triangle G}{I}\) value of -453.5 calories.

Interpreting \( \frac{\triangle G}{I} \)

\(\triangle G\) represents the change in Gibbs free energy for the transition between carbon in diamond and graphite forms. A negative value indicates that the transition process is spontaneous and favors the formation of graphite.

Analyzing the Spontaneity

Since \( \frac{\triangle G}{I} = -453.5 \text{ cal} \) is negative, this implies that the process of converting diamond to graphite releases energy. Hence, graphite is energetically more favorable and stable than diamond.

Deciding the Correct Option

From the interpretation of \( \frac{\triangle G}{I} \), the fact that graphite has a lower Gibbs free energy than diamond means it is more stable. Therefore, the correct answer is option (3).

Key concepts

carbon allotropes

Carbon is unique in that it can exist in different structural forms, known as allotropes. The most common allotropes of carbon are diamond and graphite. Each allotrope has distinct physical and chemical properties due to its unique arrangement of carbon atoms.

In graphite, carbon atoms form layers of hexagonal arrays. These layers are loosely bonded, allowing them to slide over each other easily. This makes graphite soft and a good lubricant.

In diamond, carbon atoms are arranged in a tetrahedral lattice structure. Each carbon atom forms strong covalent bonds with four other carbon atoms, creating a very hard and rigid structure. This is why diamond is the hardest known natural material.

Other, less common, carbon allotropes include fullerenes (buckyballs) and carbon nanotubes. Each allotrope's unique arrangement results in different properties and uses.

graphite stability

Graphite is generally more stable than diamond under standard conditions. This is evidenced by the negative Gibbs free energy change \( \Delta G \) when converting diamond to graphite. A negative value indicates that the reaction is spontaneous and energetically favored.

Graphite's greater stability is due to its structure. The layers of hexagonally arranged carbon atoms in graphite interact through relatively weak van der Waals forces. These weak interactions allow the layers to slide over each other, making graphite more flexible and less prone to breaking. In contrast, diamond’s rigid tetrahedral structure is energetically higher, making it less stable than graphite under normal circumstances.

Another interesting point is that although graphite is more stable, diamonds do not spontaneously turn into graphite because the activation energy for this transformation is very high. This means diamonds are kinetically stable, meaning they don’t convert to graphite rapidly despite graphite being thermodynamically more stable.

thermodynamics

Thermodynamics is the study of energy, heat, work, and their transformations. It includes concepts like Gibbs free energy, which indicates the amount of useful work obtainable from a system at constant temperature and pressure.

Gibbs free energy, denoted as \( \Delta G \), is crucial in predicting whether a reaction will occur spontaneously. If \( \Delta G \) is negative, the process is spontaneous and occurs without needing additional energy input.

The Gibbs free energy change for a process can be calculated using the equation: \[ \Delta G = \Delta H - T \Delta S \] where:

• \( \Delta H \ \) is the change in enthalpy (heat content)
• \( \Delta S \ \) is the change in entropy (disorder)
• \( T \ \) is the absolute temperature

In the case of diamond converting to graphite, the negative \( \Delta G \) value of -453.5 calories indicates that the transition releases energy and increases the system's entropy. This makes graphite more energetically favorable compared to diamond. Understanding these principles helps explain why certain materials are more stable than others and how energy dictates chemical processes.