Problem 2.53 — Entropy: Boltzmann Formula

Problem Statement

Solve the thermodynamics problem: State Boltzmann’s entropy formula and explain its physical meaning. How does it relate to the thermodynamic definition of entropy? Boltzmann’s formula: $$S = k_B\ln\Omega$$ where $\Omega$ is the number of microstates (statistical weight) corresponding to the macroscopic state. $k_B = 1.38\times10^{-

Given Information

  • See problem statement for all given quantities.

Physical Concepts & Formulas

Entropy is a state function measuring the dispersal of energy. The Second Law requires that the total entropy of an isolated system never decreases. For a reversible process, $dS = dQ_\text{rev}/T$; for irreversible processes, the actual entropy change exceeds $dQ/T$.

  • $\Delta S = \int dQ_{\text{rev}}/T$ — entropy change for reversible process
  • $\Delta S = nC_V \ln(T_2/T_1) + nR\ln(V_2/V_1)$ — ideal gas entropy change
  • $\Delta S \geq 0$ for isolated system (Second Law)

Step-by-Step Solution

Step 1 — Verify the result: Check units, limiting cases, and order of magnitude to confirm the answer is physically reasonable.

Step 2 — Verify the result: Check units, limiting cases, and order of magnitude to confirm the answer is physically reasonable.

Step 3 — Verify the result: Check units, limiting cases, and order of magnitude to confirm the answer is physically reasonable.

Worked Calculation

$$S = k_B\ln\Omega$$

Answer

$$\boxed{\eta_{\text{Carnot}} = 1 – \dfrac{T_C}{T_H}}$$

Physical Interpretation

Entropy increases in any irreversible process. The numerical result confirms the Second Law: the universe’s entropy has increased, and the process cannot spontaneously reverse.


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