States of Matter & Phase Changes

Vocabulary flashcards covering states of matter, phase transitions, thermodynamic constants, and phase diagram characteristics based on lecture notes.

Solid

State characterized by very strong attractive forces, particles that are orderly and close together, a definite volume and definite shape, and low kinetic energy with motion limited to vibrations.

Liquid

State with moderate to strong attractive forces and particles that are random but close together; it has a definite volume, takes the shape of its container, and has medium kinetic energy where particles flow.

Gas (Vapor)

State with weak or no attractive forces and particles that are random and far apart; it has no definite volume or shape and high kinetic energy where particles flow.

Temperature

A measure of average kinetic energy.

Vapor pressure

Pressure exerted by a gas above its own liquid, due to evaporation.

Boiling point

The temperature at which the vapor pressure of a liquid equals the external (atmospheric) pressure.

Viscosity

Resistance to flow.

Surface tension

Resistance to increasing surface area.

Volatile

Describes a substance that readily evaporates.

Clausius-Clapeyron equation

$\ln(P_1/P_2) = (\Delta H_{\text{vap}}/R)(1/T_2 - 1/T_1)$; this relates a substance's vapor pressure to its temperature.

$\Delta H_{\text{vap}}$ (enthalpy of vaporization)

The heat required to vaporize a substance; used in units of $J/mol$ in the Clausius-Clapeyron equation.

$R$ (gas constant, thermo)

$$8.314\,J\,mol^{-1}\,K^{-1}$$

Melting / Fusion

Phase change from solid to liquid; endothermic ($\Delta H > 0$).

Vaporization / Boiling

Phase change from liquid to gas; endothermic ($\Delta H > 0$).

Sublimation

Phase change from solid directly to gas; endothermic ($\Delta H > 0$); for example: dry ice.

Freezing

Phase change from liquid to solid; exothermic ($\Delta H < 0$).

Condensation

Phase change from gas to liquid; exothermic ($\Delta H < 0$).

Deposition

Phase change from gas directly to solid; exothermic ($\Delta H < 0$).

Endothermic

A process that absorbs (requires) energy/heat.

Exothermic

A process that releases energy/heat.

Enthalpy ($\Delta H$)

Heat, $q$, measured at constant pressure.

Specific heat ($C_s$)

The energy needed to change the temperature of $1\,\text{gram}$ of a substance by $1\,\text{degree}$.

$q$ (phase change formula)

$q = n \times \Delta H_{\text{phase change}}$; heat required for a phase change at constant temperature, using moles.

$q$ (temperature change formula)

$q = m \times C_s \times \Delta T$; heat required to change temperature within one phase, using grams.

$\Delta H_{\text{freezing}}$ vs $\Delta H_{\text{fusion}}$

$\Delta H_{\text{freezing}} = -\Delta H_{\text{fusion}}$ (freezing releases the same amount of energy that fusion/melting absorbs).

$\Delta H_{\text{condensation}}$ vs $\Delta H_{\text{vaporization}}$

$\Delta H_{\text{condensation}} = -\Delta H_{\text{vaporization}}$ (condensation releases the same amount of energy that vaporization absorbs).

Triple point

The temperature and pressure at which solid, liquid, and gas all coexist in equilibrium; the minimum pressure at which liquid can exist.

Critical point

The maximum temperature and pressure at which liquid and gas can still be distinguished as separate phases; beyond this point the substance is a supercritical fluid.

Supercritical fluid

The state of a substance beyond its critical point, where liquid and gas can no longer be distinguished.

Normal boiling point / melting point

The boiling point or melting point of a substance measured specifically at $1\,\text{atm}$.

Phase diagram

A graph of pressure vs. temperature showing which phase (solid, liquid, gas) is favored under given conditions, and the boundaries where phases coexist in equilibrium.

Positive slope (solid-liquid line)

Indicates the solid is denser than the liquid ($d_{\text{solid}} > d_{\text{liquid}}$); the normal case for most substances.

Negative slope (solid-liquid line)

Indicates the liquid is denser than the solid ($d_{\text{liquid}} > d_{\text{solid}}$); the anomalous case, seen in water.