Chemical Thermodynamics in Molecular Systems

Manual: General · Subject: Molecular Science

Analyze energetic and entropic factors that drive molecular processes.

Energy, Work, and Spontaneity

Thermodynamic Language

Molecular processes are governed by changes in enthalpy, entropy, and Gibbs free energy. The key relationship is $\Delta G = \Delta H - T\Delta S$ ; a process is spontaneous when $\Delta G < 0$ under the given conditions.

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Interpretation

A spontaneous process is not necessarily fast. Thermodynamics predicts favorability, while kinetics predicts rate.

If a process has $\Delta H < 0$ and $\Delta S > 0$ , what is true at all temperatures?

It is never spontaneous It is always spontaneous It is spontaneous only at low temperature It requires activation energy

What does a positive value of $\Delta S$ indicate?

Bond Energies and Reaction Enthalpy

Estimating Reaction Heat

Reaction enthalpy can be approximated from bond energies: break bonds first, then form bonds. If the energy released in bond formation exceeds the energy required to break bonds, the reaction is exothermic.

A reaction breaks bonds requiring $200\,\mathrm{kJ/mol}$ and forms bonds releasing $260\,\mathrm{kJ/mol}$ . What is $\Delta H$ approximately?

-60\,\mathrm{kJ/mol}

+60\,\mathrm{kJ/mol}

-460\,\mathrm{kJ/mol}

+460\,\mathrm{kJ/mol}

What kind of thermodynamic quantity is $\Delta G$ ?

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Memory Deck

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Concept Constellation

Chemical Thermodynamics in Molecular Systems

Energy, Work, and Spontaneity

Thermodynamic Language

Bond Energies and Reaction Enthalpy

Estimating Reaction Heat