Chem 2 – Core Concepts & Vocabulary (Pre-Class Set)

Enthalpy (ΔH)

Heat content of a system at constant pressure

Exothermic reaction

Reaction that releases heat to surroundings (ΔH < 0)

Endothermic reaction

Reaction that absorbs heat from surroundings (ΔH > 0)

Entropy (ΔS)

Measure of disorder or randomness in a system

Second Law of Thermodynamics

Total entropy of the universe always increases

Gibbs Free Energy (ΔG)

Energy available to do useful work

Standard conditions

1 atm pressure, 1 M concentrations, 25°C

State function

A property that depends only on initial and final states, not the reaction path.

Hess’s Law

Overall enthalpy change equals sum of individual steps

Reaction rate

Change in concentration of reactant or product per unit time

Rate law

Mathematical expression relating rate to reactant concentrations

Rate constant (k)

Proportionality constant in the rate law

Reaction order

Power to which concentration is raised in the rate law

Overall reaction order

Sum of individual reactant orders

Elementary step

Single-step reaction in a mechanism

Reaction mechanism

Sequence of elementary steps in a reaction

Activation energy (Ea)

Minimum energy required for reaction to occur

Catalyst

Substance that increases rate without being consumed

Transition state

High-energy configuration between reactants and products

First Law of Thermodynamics

Energy cannot be created or destroyed, only transferred or transformed.

Equilibrium constant (K)

Ratio of product to reactant concentrations at equilibrium

Reaction quotient (Q)

Same form as K but for non-equilibrium conditions

Le Châtelier’s Principle

System shifts to counteract applied stress

Homogeneous equilibrium

All species in same phase

Heterogeneous equilibrium

Species in different phases

Equilibrium position

Relative amounts of reactants and products at equilibrium

Arrhenius acid

Substance that produces H⁺ in water

Arrhenius base

Substance that produces OH⁻ in water

Brønsted–Lowry acid

Proton (H⁺) donor

Brønsted–Lowry base

Proton (H⁺) acceptor

Conjugate acid

Species formed when a base gains a proton

Conjugate base

Species formed when an acid loses a proton

Lewis acid

Electron pair acceptor

Lewis base

Electron pair donor

Strong acid

Completely ionizes in water

Weak acid

Partially ionizes in water

pH

Measure of acidity based on hydrogen ion concentration

pOH

Measure of basicity based on hydroxide ion concentration

Autoionization of water

Water molecules react to form H⁺ and OH⁻

Ion product of water (Kw)

Product of [H⁺][OH⁻] at equilibrium

Buffer

Solution that resists changes in pH

Common ion effect

Suppression of ionization due to shared ion

Oxidation

Loss of electrons

Reduction

Gain of electrons

Redox reaction

Reaction involving electron transfer

Anode

Electrode where oxidation occurs

Cathode

Electrode where reduction occurs

Galvanic cell

Cell that produces electrical energy from spontaneous reaction

Electrolytic cell

Cell that uses electrical energy to drive reaction

Cell potential

Measure of voltage produced by a cell

Electronegativity

Ability of an atom to attract electrons

Electronegativity difference (ΔEN)

Difference in electronegativity between bonded atoms

Polar bond

Covalent bond with unequal electron sharing

Nonpolar bond

Covalent bond with equal electron sharing

Partial charge (δ⁺ / δ⁻)

Slight positive or negative charge in a polar bond

Charge separation

Spatial separation of partial charges in a molecule

Molecular polarity

Overall charge distribution of a molecule

Molecular geometry

Three-dimensional arrangement of atoms

Electron domain

Region of electron density around a central atom

Symmetrical molecule

Shape where dipoles cancel

Asymmetrical molecule

Shape where dipoles do not cancel

Intermolecular forces (IMF)

Attractions between molecules

Dipole–dipole forces

Attractions between polar molecules

Hydrogen bonding

Strong dipole–dipole involving H bonded to N, O, or F

London dispersion forces

Weak attractions from temporary dipoles

Ion–dipole forces

Attraction between ion and polar molecule

Spontaneous

Thermodynamically favored, not necessarily fast

Dynamic equilibrium

Continuous forward and reverse reactions

Work

energy transferred by force acting over a distance

Heat

energy transferred due to a temperature difference

Calorimetry

measurement of heat flow using temperature changes

Standard enthalpy of formation

enthalpy change when 1 mole of a compound forms from its elements in their standard states

Sigma Σ

sum of multiple terms

Matter

Anything that has mass and occupies volume

Pure substance

Matter with a fixed, definite composition

Mixture

Physical combination of substances with variable composition

Homogeneous mixture

Mixture with uniform composition throughout

Heterogeneous mixture

Mixture with non-uniform composition

Solution

Homogeneous mixture of solute dissolved in solvent

Solvent

Substance that dissolves the solute

Solute

Substance that is dissolved

Aqueous

Dissolved in water

Base unit of mass

gram (g)

Base unit of length

meter (m)

Base unit of volume

liter (L)

Base unit of amount

mole (mol)

Base unit of temperature

kelvin (K)

kilo (k)

10³

centi (c)

10⁻²

milli (m)

10⁻³

micro (µ)

10⁻⁶

Kilogram to gram

1 kg = 1000 g

Gram to milligram

1 g = 1000 mg

Meter to centimeter

1 m = 100 cm

Centimeter to millimeter

1 cm = 10 mm

Kilometer to meter

1 km = 1000 m

Liter to milliliter

1 L = 1000 mL

Kilojoule to joule

1 kJ = 1000 J