The translational entropy dominates when bonds are broken
An entropy change has four contributions\Delta S^\circ=\Delta S^{Molecular}+\Delta S^{\circ,Translation}+\Delta S^{Rotation}+\Delta S^{Vibration}For reactions where bonds are broken S^{\circ,Translation} usually dominates.
For example for the reaction H_2 \rightarrow 2H the entropy changes at 25 ^\circC are:\Delta S^\circ = 11.6+100.1-12.8-0.0=98.9 \text{ J/molK}For breaking the hydrogen bond between two water molecules, H_2O\cdot \cdot \cdot HOH\rightarrow 2H_2O, the free energy energy contributions are\Delta S^\circ =0.0+136.2+9.3-66.0=79.4 \text{ J/molK}In both cases \Delta S^\circ is positive because two particles have more entropy than one.
In many cases \Delta S^\circ \approx \Delta S^{\circ,Translation} is a reasonable approximation.
Test: What happens to the standard entropy for this process
An entropy change has four contributions\Delta S^\circ=\Delta S^{Molecular}+\Delta S^{\circ,Translation}+\Delta S^{Rotation}+\Delta S^{Vibration}For reactions where bonds are broken S^{\circ,Translation} usually dominates.
For example for the reaction H_2 \rightarrow 2H the entropy changes at 25 ^\circC are:\Delta S^\circ = 11.6+100.1-12.8-0.0=98.9 \text{ J/molK}For breaking the hydrogen bond between two water molecules, H_2O\cdot \cdot \cdot HOH\rightarrow 2H_2O, the free energy energy contributions are\Delta S^\circ =0.0+136.2+9.3-66.0=79.4 \text{ J/molK}In both cases \Delta S^\circ is positive because two particles have more entropy than one.
In many cases \Delta S^\circ \approx \Delta S^{\circ,Translation} is a reasonable approximation.
Test: What happens to the standard entropy for this process
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