Q. No.25. At a given pressure, a substance is heated from 2000 K to 2600 K. If the entropy of the substance is 60 J K-1 mol-1, and is assumed to be constant over the given temperature range, then the change in the chemical potential (in kJ mol-1) of the substance is __________.
The change in chemical potential is -36 kJ mol-1. This numerical fill-in-the-blank question from thermodynamics assesses the temperature dependence of chemical potential at constant pressure with constant molar entropy.
Thermodynamic Basis
Chemical potential μ equals the molar Gibbs free energy gm, so (∂μ/∂T)P = -sm (∂T/∂μ)P = -sm from the Gibbs-Duhem equation, where sm is molar entropy. Integrating at constant pressure and constant sm gives Δμ = μ(T2) – μ(T1) = -sm(T2 – T1). Here, T1 = 2000 K, T2 = 2600 K, and sm = 60 J K-1 mol-1 = 0.060 kJ K-1 mol-1, so ΔT = 600 K and Δμ = -0.060 × 600 = -36 kJ mol-1.
Detailed Solution Steps
Identify conditions: Constant pressure, sm constant over range.
Apply relation: dμ = -sm dT (at constant P).
Integrate: ∫μ1μ2 dμ = -sm ∫20002600 dT.
Compute: Δμ = -60 × 10-3 × 600 = -36 kJ mol-1.
Why No Options?
This is a numerical response question requiring exact computation, common in exams like CSIR NET Life Sciences for thermodynamics applications in biochemical systems. No multiple choices; fill -36 (or -36.0 if decimals expected).
Key Concepts
Chemical potential μ drives phase stability and reactions. At constant pressure:
dμ = -S dT + V dP, simplifies to dμ = -sm dT.
Constant sm assumption holds for narrow ranges or ideal cases.
Step-by-Step Calculation
Note ΔT = 2600 – 2000 = 600 K.
sm = 60 J K-1 mol-1 = 0.060 kJ K-1 mol-1.
Δμ = -sm ΔT = -0.060 × 600 = -36 kJ mol-1.
This negative value indicates lower μ at higher T, favoring reactions or phase changes.
CSIR NET Relevance
Such problems test integration of partial derivatives in biochemical contexts like protein stability or enzyme kinetics under high-temperature conditions. Practice similar derivations for scoring in Physical Chemistry section.


