Question:
The equation that describes how the extent of phase transformation changes with time is known as
The equation that describes how the extent of phase transformation changes with time is known as
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Avrami equation is the standard model for solid-state transformation kinetics.
Updated On: Jun 29, 2026
- Arrhenius equation
- Gibbs phase rule
- Clausius-Clapeyron equation
- Avrami equation
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The Correct Option is D
Solution and Explanation
Concept:
The kinetics of phase transformation describes how the fraction of transformed material changes with time under isothermal conditions.
The most widely used model is the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory, commonly called the Avrami equation.
Step 1: Avrami equation form.
\[ X(t) = 1 - e^{-kt^n} \] where:
• $X(t)$ = fraction transformed
• $k$ = rate constant
• $n$ = Avrami exponent (depends on mechanism)
Step 2: Physical meaning.
The equation accounts for:
• nucleation rate
• growth rate
• impingement of growing particles It fully describes transformation kinetics.
Step 3: Why others are incorrect.
• Arrhenius → temperature dependence of rate constant
• Gibbs phase rule → equilibrium degrees of freedom
• Clausius-Clapeyron → phase equilibrium slope Final Answer: \[ \boxed{\text{Avrami equation}} \]
Step 1: Avrami equation form.
\[ X(t) = 1 - e^{-kt^n} \] where:
• $X(t)$ = fraction transformed
• $k$ = rate constant
• $n$ = Avrami exponent (depends on mechanism)
Step 2: Physical meaning.
The equation accounts for:
• nucleation rate
• growth rate
• impingement of growing particles It fully describes transformation kinetics.
Step 3: Why others are incorrect.
• Arrhenius → temperature dependence of rate constant
• Gibbs phase rule → equilibrium degrees of freedom
• Clausius-Clapeyron → phase equilibrium slope Final Answer: \[ \boxed{\text{Avrami equation}} \]
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