Entropy
Related Examples and Practice Problems
Additional Worked Out Examples/ Practice
Identifying classification types: Differentiation between elements, compounds or mixtures and homogeneous and heterogenous mixtures
Separation techniques: Selected and explaining limitation of appropriate separation
Relating Properties to Composition: Predicting classification based on descriptive properties
Topic Summary & Highlights
and Help Videos
Core Concept
Entropy (S) is a thermodynamic quantity that measures the degree of randomness or disorder in a system.
Key Idea: The greater the number of possible arrangements (microstates) for a system, the higher its entropy.
Practice Tips
Entropy measures disorder and energy dispersal in a system.
Spontaneous processes increase the total entropy of the universe.
Factors like phase changes, temperature, and molecular complexity affect entropy.
The relationship between entropy, enthalpy, and temperature determines spontaneity through Gibbs free energy.
Factors Affecting Entropy
Phase Changes:
Solid →\rightarrow→ Liquid →\rightarrow→ Gas: Entropy increases.
Example: Melting and boiling increase entropy because molecules have more freedom of motion.
Temperature:
Entropy increases as temperature increases because molecules move more rapidly and occupy more possible energy levels.
Molecular Complexity:
Larger, more complex molecules have higher entropy because they can vibrate, rotate, and arrange themselves in more ways.
Mixing:
Mixing substances (e.g., dissolving salt in water) increases entropy because the components are more dispersed.
Entropy in Chemical Reactions
Standard Molar Entropy (S∘S^\circS∘):
The entropy of 1 mole of a substance at a standard state (298 K, 1 atm).
Units: J/K\cdotpmol\text{J/K·mol}J/K\cdotpmol.
Change in Entropy (ΔS∘\Delta S^\circΔS∘): ΔS∘=∑Sproducts∘−∑Sreactants∘\Delta S^\circ = \sum S^\circ_{\text{products}} - \sum S^\circ_{\text{reactants}}ΔS∘=∑Sproducts∘−∑Sreactants∘
Spontaneity and Entropy:
A process is spontaneous if ΔSuniverse>0\Delta S_{\text{universe}} > 0ΔSuniverse>0.
Key Characteristics of Entropy
Units: Entropy is measured in J/K·mol (joules per kelvin per mole).
Symbol: S
State Function: Entropy depends only on the state of the system, not the path taken to reach that state.
Entropy and Disorder: Systems with more disorder or freedom of movement have higher entropy (e.g., gases have more entropy than liquids, which have more entropy than solids).
Second Law of Thermodynamics
Statement: The total entropy of the universe (ΔSuniverse\Delta S_{\text{universe}}ΔSuniverse) always increases in a spontaneous process. ΔSuniverse=ΔSsystem+ΔSsurroundings>0\Delta S_{\text{universe}} = \Delta S_{\text{system}} + \Delta S_{\text{surroundings}} > 0ΔSuniverse=ΔSsystem+ΔSsurroundings>0
