Question

Compared to homogeneous nucleation, the activation free energy required for heterogeneous nucleation is

• A. Lower
• B. Same
• C. Higher
• D. Independent of temperature

Hint:

Impurities and surfaces act as nucleation catalysts.

Answer 1

The Correct Option is A

Concept: Nucleation is the first step in phase transformation where a stable nucleus of a new phase is formed. The energy barrier for nucleation is called activation free energy. There are two types:
• Homogeneous nucleation (inside bulk)
• Heterogeneous nucleation (at surfaces/interfaces)

Step 1: Homogeneous nucleation energy barrier.
In homogeneous nucleation:
• nucleus forms in bulk material
• requires high energy barrier
• no assistance from surfaces So activation energy is maximum.

Step 2: Heterogeneous nucleation.
In heterogeneous nucleation:
• occurs on container walls, grain boundaries, impurities
• surface reduces interfacial energy
• lowers energy barrier

Step 3: Comparison.
\[ \Delta G^*_{heterogeneous} < \Delta G^*_{homogeneous} \] Thus heterogeneous nucleation is energetically easier. Final Answer: \[ \boxed{\text{Lower}} \]