Entropy and Thermodynamics Flashcards

Vocabulary flashcards covering entropy, the Second and Third Laws of Thermodynamics, reaction spontaneity, and qualitative factors affecting entropy.

Entropy ($S$)

A measurement of order/disorder, or a measurement of randomness in a system.

Second Law of Thermodynamics

States that the entropy of the universe is always increasing, expressed as $\text{Δ}S_{\text{universe}} = \text{Δ}S_{\text{system}} + \text{Δ}S_{\text{surrounding}} > 0$.

Third Law of Thermodynamics

States that the entropy of a pure crystalline substance at absolute zero ($0\,\text{K}$) is equal to zero.

Spontaneous Reaction

A reaction that can occur on its own without continued outside interference (work). Spontaneity is independent of reaction rate, activation energy, speed, sensitivity, and volatility.

Non-Spontaneous Process

A process that cannot occur without continued outside interference; if a process is spontaneous in one direction, it is non-spontaneous in the reverse direction under the same conditions.

Temperature Effect on Entropy

Entropy is proportional to enthalpy and temperature; heating up a system increases entropy because faster-moving molecules are more random.

Phase Change Trend in Entropy

Entropy increases when transitioning from solid to liquid, aqueous, and gas phases, following the order $S_{(s)} < S_{(l)} < S_{(aq)} < S_{(g)}$.

Entropy Change of Dissolving

Dissolving a solid $(s)$ in water to form an aqueous solution $(aq)$ increases entropy ($\uparrow S$), whereas dissolving a gas $(g)$ in water decreases entropy.

Moles of Particles Effect on Entropy

A reaction where the number of moles of product particles is greater than the number of moles of reactant particles results in greater entropy ($\Delta S > 0$).

Volume Effect on Entropy

A greater volume allows for greater particle dispersion and disorder, which increases entropy ($\uparrow S$).

Molecular Mass and Complexity Effect on Entropy

Entropy generally increases with greater molar mass and molecular complexity because more microstates become available (e.g., $S_{\text{SO}_2(g)} < S_{\text{SO}_3(g)}$ and $S_{\text{O}_2} < S_{\text{O}_3}$).