Entropy, Free Energy, and Spontaneity

Manual: General · Subject: Chemistry

Connect disorder, energy dispersal, and equilibrium with Gibbs free energy.

Why some processes happen

Entropy

Entropy, $S$ , measures the dispersal of energy and the number of accessible microstates. Systems tend to evolve toward arrangements with greater overall entropy, especially when energy becomes more spread out.

Gibbs free energy

At constant temperature and pressure, spontaneity is determined by $\Delta G = \Delta H - T\Delta S.$ A process is spontaneous when $\Delta G < 0$ .

Interpreting free energy

Condition	Spontaneity
$\Delta G < 0$	Spontaneous
$\Delta G = 0$	At equilibrium
$\Delta G > 0$	Nonspontaneous in the forward direction

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Temperature matters

A reaction with $\Delta H > 0$ and $\Delta S > 0$ may become spontaneous at high temperature because the $T\Delta S$ term can outweigh the enthalpy cost.

If $\Delta G < 0$ , the forward process is

Impossible Spontaneous At equilibrium Always fast

Write the Gibbs free energy equation.

Spontaneity vs rate

Spontaneity

Thermodynamic concept
Describes whether a process is favored overall
Determined by $\Delta G$

Rate

Kinetic concept
Describes how fast a process occurs
Determined by the reaction pathway and activation energy

A reaction with $\Delta H < 0$ and $\Delta S < 0$ is most favored at

High temperature Low temperature Any temperature equally Never

Neuroanatomy Explorer

Memory Deck

Match the Pairs

Concept Constellation

Entropy, Free Energy, and Spontaneity

Why some processes happen

Entropy

Gibbs free energy

Spontaneity vs rate