AP Chemistry Unit 9: Entropy, Free Energy, and Favorability

What is Thermodynamics?

The study of energy and its interconversions.

What does Enthalpy ($\Delta H$) indicate?

Enthalpy indicates heat flow but does not predict if a reaction will occur naturally.

How is Entropy ($S$) defined?

Entropy is a measure of the dispersal of matter and energy, often associated with disorder or randomness.

What are Microstates?

Microstates are the specific configurations of all atom positions and energies at a given instant.

What is the Second Law of Thermodynamics?

The entropy of the universe increases in any thermodynamically favorable process.

What is the effect of the state of matter on Entropy?

Entropy is highest in gases, followed by liquids, and lowest in solids.

How does temperature affect Entropy?

Entropy increases as temperature increases due to higher kinetic energy and distribution of molecular speeds.

How does volume affect Entropy?

Entropy increases as volume increases, allowing for more possible positions for particles.

What is the Third Law of Thermodynamics?

The entropy of a perfect crystal at absolute zero (0 K) is exactly zero.

How is the standard entropy change ($\Delta S^\circ_{rxn}$) calculated?

$\Delta S^\circ{rxn} = \Sigma S^\circ{products} - \Sigma S^\circ_{reactants}$.

What does a positive $\Delta S$ indicate?

It indicates that matter is becoming more dispersed.

What does a negative $\Delta S$ indicate?

It indicates that matter is becoming more ordered or constrained.

What is Gibbs Free Energy ($G$)?

Gibbs Free Energy combines enthalpy and entropy to predict thermodynamic favorability.

What is the Gibbs-Helmholtz Equation?

$\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ$.

What does $\Delta G < 0$ signify?

It signifies that the process is thermodynamically favorable (spontaneous).

What does $\Delta G > 0$ signify?

It signifies that the process is thermodynamically unfavorable (non-spontaneous).

What is the key to interpreting signs of $\Delta G$?

The sign of $\Delta G$ determines whether a process is favorable or unfavorable.

What is Kinetic Control in reactions?

A reaction is under kinetic control if it has a large negative $\Delta G$ but occurs slowly due to high activation energy.

What does $\Delta G^\ imes$ tell us?

It tells us about the favorability from standard states to equilibrium.

What is the relationship between $\Delta G^\ imes$ and the equilibrium constant $K$?

$\Delta G^\circ = -RT \ln K$.

What does it mean if $K > 1$?

It means that the equilibrium favors products.

What does it mean if $K < 1$?

It means that the equilibrium favors reactants.

What is a coupled reaction?

A process where two reactions share a common intermediate to make an overall process thermodynamically favorable.

What common mistake involves temperature units?

Using Celsius instead of Kelvin; always convert using $K = ^\circ C + 273.15$.

How should units be handled in the Gibbs Free Energy equation?

Ensure to convert $\Delta S$ from J to kJ or $\Delta H$ from kJ to J before calculating.

What is common about standard Gibbs Free Energy and equilibrium conditions?

$\Delta G^\ imes$ is for standard conditions while $\Delta G$ is at equilibrium.

What does $\Delta G = 0$ imply?

The system is in equilibrium.