Phases Lecture Notes

Flashcards summarizing key concepts from a lecture on phases and phase transitions, focusing on thermodynamics and Gibbs energy.

What is the Gibbs energy?

A measure of the amount of energy available in a chemical or physical system to do useful work at a constant temperature and pressure.

Give the Gibbs energy equation.

G = H - TS (Gibbs energy equals enthalpy minus temperature times entropy).

What is the difference between delta u and du?

Delta u refers to the difference in internal energy between two states, while du refers to an infinitesimally small change in internal energy.

What does the master equation link?

Changes in Gibbs energy (dG) to changes in pressure (dP) and temperature (dT), relating them to volume and entropy.

Why is Gibbs energy important in the context of phase changes?

It helps determine whether a phase change will occur spontaneously and which phase is most stable under specific conditions of pressure and temperature.

If temperature is constant, how does pressure affect Gibbs energy?

As pressure increases, Gibbs energy also increases, due to the positive molar volume, which describes the amount of space that a mole of material takes up.

Why is the Gibbs energy of a gas more sensitive to changes in pressure compared to liquids and solids?

Because the molar volume of a gas changes significantly with pressure, whereas the molar volumes of liquids and solids are relatively constant.

What does the gradient of a Gibbs energy vs. pressure plot represent?

Molar volume. Steeper gradients indicate greater sensitivity to pressure changes.

If pressure is constant, how does temperature affect Gibbs energy?

As temperature increases, Gibbs energy decreases, due to the negative relationship involving entropy.

How does molar entropy differ between gases, liquids, and solids?

Molar entropy is highest for gases, followed by liquids, and lowest for solids, reflecting the degree of disorder or freedom of molecular arrangement.

What is a key characteristic of Gibbs energy at phase boundaries?

At the phase boundary, the molar Gibbs energy is the same for both phases in equilibrium.

Why are phase diagrams useful?

They map out phase transitions as a function of temperature and pressure, providing a visual guide to the stable phases of a substance under different conditions.

What is the Gibbs Phase Rule?

An equation (F = C - P + 2) that relates the number of degrees of freedom (F) to the number of components (C) and phases (P) in a system at equilibrium.

What does the Clapeyron relation describe?

The relationship between the slope of a phase boundary on a phase diagram and the enthalpy and volume changes associated with the phase transition.

What is the Clausius-Clapeyron relation particularly useful for?

Estimating the vapor pressure or boiling point of a liquid at different temperatures, especially for transitions involving a gas phase.

What is Trouton's rule?

The entropy of vaporization is usually about 85 joules per Kelvin per mole.

What do deviations from Trouton's rule indicate?

Suggest unusual molecular interactions in the liquid or gas phase, such as hydrogen bonding or molecular association.