Heating Curves, Vapor Pressure, and Phase Diagrams

Key vocabulary terms covering thermochemistry heat transfers, vapor pressure equilibria, intermolecular forces, and phase diagram characteristics from the lecture transcript.

Freezing and Fusion

Reverse phase processes that share the same numerical value of heat ($\Delta H$) but carry opposite signs: freezing is an exothermic process ($-\Delta H$), while fusion is an endothermic process ($+\Delta H$).

State of Equilibrium

The condition reached when the rates of two reverse processes (such as evaporation and condensation) are equal, leading to no observable net change on the macroscopic level.

Vapor Pressure

The partial pressure exerted by a gas once a state of dynamic equilibrium between evaporation and condensation is obtained.

Volatility

The tendency of a liquid to evaporate; volatile liquids typically have weaker intermolecular forces ($\text{IMFs}$) and exhibit higher vapor pressures.

Maxwell-Boltzmann Distribution

A well-characterized statistical distribution showing the spread of molecular kinetic energies within a given sample of matter.

Normal Boiling Point

The temperature at which a substance boils under an ambient pressure of exactly $1\,\text{atm}$ (such as $373\,\text{K}$ for water).

Boiling Point

The temperature at which the vapor pressure of a liquid becomes equal to the external ambient pressure.

Coexistence Curves

Lines on a phase diagram mapping the specific combinations of pressure and temperature under which two states of matter can simultaneously coexist.

Triple Point

The unique combination of temperature and pressure on a phase diagram where all coexistence curves meet and all three phases of matter exist simultaneously.

Critical Point

The point where the liquid-gas boundary curve terminates on a phase diagram, marking the threshold where the liquid and gas phases attain identical density.

Supercritical Fluid

A state of matter occurring at temperatures and pressures beyond the critical point, where distinct liquid and gas phases do not exist.

Sublimation

The phase transition in which a substance converts directly from a solid to a gas, as seen with dry ice ($\text{solid } CO_2$) at atmospheric pressure.