CH301 Unit 3: Gases, States of Matter, and Intermolecular Forces

Vocabulary practice flashcards covering eponymous gas laws, the ideal gas law, stoichiometry, kinetic molecular theory, gas non-ideality, intermolecular forces, liquid properties, and solid classifications.

Boyle's Law

A gas law stating that pressure and volume have an inverse relationship at constant temperature and moles, expressed as $P_1V_1 = P_2V_2$.

Charles' Law

A gas law stating that volume and temperature have a direct relationship at constant pressure and moles, expressed as $\frac{V_1}{T_1} = \frac{V_2}{T_2}$.

Avogadro's Law

A gas law stating that equal volumes of gases at the same temperature and pressure contain equal numbers of moles, expressed as $\frac{V_1}{n_1} = \frac{V_2}{n_2}$.

Gay-Lussac's Law

A gas law stating that pressure and temperature have a direct relationship at constant volume, expressed as $\frac{P_1}{T_1} = \frac{P_2}{T_2}$, and that reactant and product gas volumes combine in whole-number ratios.

Combined Gas Law

A gas law relating pressure, volume, and temperature for a fixed amount of gas, expressed as $\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}$.

Ideal Gas Law

The equation of state of a hypothetical ideal gas that relates pressure, volume, amount in moles, and temperature via the equation $PV = nRT$.

Gas Molecular Weight Equation

A derived form of the ideal gas law used to calculate molar mass ($MW$) from gas mass ($m$), pressure ($P$), volume ($V$), and temperature ($T$): $MW = \frac{mRT}{PV}$.

Gas Density ($\rho$)

The mass per unit volume of a gas, derived from the ideal gas law as $\rho = \frac{m\cdot P}{n\cdot RT} = \frac{PMW}{RT}$.

Dalton's Law of Partial Pressures

A gas law stating that the total pressure exerted by a mixture of ideal gases equals the sum of the partial pressures of each individual gas component: $P_{tot} = P_1 + P_2 + P_3 + \dots$.

Mole Fraction

The ratio of the number of moles of one component to the total number of moles in a gas mixture, which is directly proportional to its contribution to total pressure.

Combustion Reaction

A reaction associated with burning fuel where a hydrocarbon ($\text{C}_X\text{H}_Y$) reacts with oxygen ($\text{O}_2$) to produce carbon dioxide ($\text{CO}_2$) and water ($\text{H}_2\text{O}$).

Molar Volume at STP

The constant ratio stating that one mole of any ideal gas occupies $22.4\,L$ of volume at Standard Temperature and Pressure ($\frac{22.4\,L}{1\,mol}$).

Kinetic Molecular Theory (KMT)

A model based on five assumptions: gases are hard spheres, have no volume, undergo elastic collisions with no intermolecular forces, have average kinetic energy proportional to temperature ($KE = \frac{1}{2}kT$), and have velocities inversely related to square root of mass ($KE = \frac{1}{2}mv^2$).

Elastic Collision

A collision between gas particles in which no kinetic energy is lost and particles do not stick together or react due to an absence of intermolecular forces.

Maxwell-Boltzmann Distribution

A statistical distribution showing the range of molecular velocities for a gas, which broadens as temperature increases or as molar mass decreases.

Graham's Law

A law stating that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molecular weight, expressed as $\frac{v_1}{v_2} = \sqrt{\frac{MW_2}{MW_1}}$.

Effusion

The movement of gas particles passing through a tiny hole into an evacuated chamber or area of lower pressure.

Diffusion

The gradual spread of gas molecules through another gas or space from high concentration to low concentration via random thermal motion.

van der Waals Equation

An equation modifying the ideal gas law to account for real gas behavior by correcting for intermolecular attractions and finite molecular volume: $\left(P + a\frac{n^2}{V^2}\right)(V - nb) = nRT$.

van der Waals Parameter $a$

A constant in the van der Waals equation correcting for intermolecular attractions ("stickiness"); larger and more polar molecules exhibit higher values of $a$.

van der Waals Parameter $b$

A constant in the van der Waals equation correcting for the actual volume occupied by gas particles; larger molecules with higher molecular weights exhibit higher values of $b$.

Intramolecular Forces

Chemical bonds holding atoms together within a single molecule or unit, such as single, double, triple covalent bonds, or ionic bonds (~$400$ to >$800\,kJ\,mol^{-1}$).

Intermolecular Forces (IMFs)

Attractive forces between separate molecules (~$1$ to $100\,kJ\,mol^{-1}$) that determine bulk physical properties such as boiling point, viscosity, and surface tension.

Dispersion Forces

Intermolecular forces arising from temporary instantaneous dipoles formed by asymmetric electron distributions; present in all molecules and dominant in nonpolar molecules.

Constitutional Isomers

Molecules with identical molecular formulas but different atom connectivity; less branched isomers have greater surface area and stronger dispersion forces than compact, branched isomers.

Dipole-Dipole Forces

Intermolecular attractive forces occurring between the permanent dipoles of polar molecules, which strengthen as the sum of electronegativity differences increases.

Hydrogen Bonding

An unusually strong type of dipole-dipole attraction occurring specifically when hydrogen is bonded directly to nitrogen ($N$), oxygen ($O$), or fluorine ($F$).

Boiling Point

A bulk liquid phenomenon where vapor pressure equals atmospheric pressure, causing liquid to convert to vapor; directly proportional to intermolecular force strength.

Surface Tension

A surface phenomenon representing the inward force that must be overcome to expand the surface area of a liquid; directly proportional to intermolecular force strength.

Capillary Action

The spontaneous movement of a liquid climbing the walls of a narrow container due to intermolecular adhesive and cohesive forces; directly proportional to intermolecular force strength.

Viscosity

The tendency of a liquid to resist flowing or pouring due to intermolecular attraction within the bulk liquid; directly proportional to intermolecular force strength.

Enthalpy of Vaporization ($\Delta H_{vap}$)

The energy required to overcome intermolecular forces for molecules at the liquid surface to transition to the gas phase; directly proportional to intermolecular force strength.

Vapor Pressure

The pressure exerted by gas molecules in equilibrium above the surface of their liquid; inversely proportional to intermolecular force strength.

Evaporation Rate

The rate at which molecules escape from the surface of a liquid into the vapor phase; inversely proportional to intermolecular force strength.

Metallic Solids

Solids composed of metal elements located toward the bottom left of the periodic table (e.g., $\text{Fe}$, $\text{Pb}$, $\text{Na}$, $\text{Nb}$), held together by metallic bonding.

Ionic Solids

Solids composed of metal cations and nonmetal anions forming a crystalline salt lattice (e.g., $\text{NaCl}$, $\text{Al}_2\text{O}_3$) whose melting points increase with higher charge density.

Covalent Network Solids

Solids consisting of vast three-dimensional arrays of covalently bonded atoms (e.g., diamond, graphite, $\text{SiO}_2$), characterized by extremely high melting points (>$1600^\circ\text{C}$ to >$3500^\circ\text{C}$).

Molecular Solids

Solids formed by small molecules held together by weak intermolecular forces at low temperatures (e.g., solid $\text{H}_2\text{O}$, solid $\text{CO}_2$, $\text{I}_2$), exhibiting low melting points typically well below $300^\circ\text{C}$.

Charge Density

The ratio of ionic charge to ionic size, which governs the lattice energy and melting point of ionic solids; higher charge and smaller radius produce higher melting points.