Chemical Equilibrium, Electrochemistry, and Organic Materials

Comprehensive vocabulary flashcards covering chemical equilibrium, acid-base theories, electrochemical cells, redox processes, industrial chemical synthesis, and organic macromolecular structures.

Open System

A chemical system that exchanges both energy and matter with its surroundings.

Closed System

A chemical system that exchanges only energy with its surroundings, which is required for establishing dynamic chemical equilibrium.

Dynamic Equilibrium

A state reached by reversible reactions in a closed system where the forward and reverse reactions occur continuously, simultaneously, and at equal rates, resulting in constant concentrations and unchanging macroscopic properties.

Reaction Reversibility

The property of a reaction to proceed in both directions; it requires sufficient energy to overcome the activation energies ($E_a$) of both the forward and reverse reactions, and is unlikely when the forward and reverse activation energies differ substantially.

Equilibrium Constant ($K_c$)

The numerical value indicating the relationship between product and reactant concentrations at equilibrium, where $Q > K_c$ indicates the system lies to the right of equilibrium and must shift left, and $Q < K_c$ indicates it lies to the left and must shift right.

Solubility Product ($K_{sp}$)

An equilibrium constant providing a measure of the solubility of an ionic compound in a saturated solution; a larger $K_{sp}$ indicates a more soluble compound.

Monoprotic Acid

An acid capable of donating only one proton ($H^+$) per molecule to a base during an acid-base reaction.

Polyprotic Acid

An acid capable of donating more than one proton ($H^+$) per molecule to a base in stepwise reactions.

Strong Acid

An acid that fully dissociates in water, yielding a high $[H^+]$ and a low pH ($0-2$); examples include hydrochloric acid ($HCl$), nitric acid ($HNO_3$), and sulfuric acid ($H_2SO_4$).

Weak Acid

An acid that incompletely or partially dissociates in aqueous solution, releasing fewer $H^+$ ions and having a higher pH ($4-6$); examples include carboxylic acids ($-COOH$) and carbonic acid ($H_2CO_3$).

Strong Base

A base that completely dissociates in water, producing a high $[OH^-]$ and a high pH ($12-14$); examples include Group 1 hydroxides ($LiOH$, $NaOH$, $KOH$, $RbOH$) and barium hydroxide ($Ba(OH)_2$).

Weak Base

A base that accepts hydrogen ions from acids to a limited extent and partially dissociates, releasing fewer $OH^-$ ions and leading to a lower pH ($8-11$); examples include ammonia ($NH_3$) and amines.

Self-Ionisation Constant of Water ($K_w$)

The equilibrium constant for the self-ionisation of water ($2H_2O(l) \rightleftharpoons H_3O^+(aq) + OH^-(aq)$), expressed as $K_w = [H^+][OH^-] = 1 \times 10^{-14}$ at $25^{\circ}\text{C}$.

Brønsted-Lowry Model

An acid-base model defining an acid as a substance that donates a proton ($H^+$) to a base, and a base as a substance that accepts a proton from an acid.

Amphiprotic Species

A substance that can either donate or accept protons, allowing it to act as either a Brønsted-Lowry acid or base.

Buffer

A solution conjugate in nature (typically a weak acid with its conjugate base, or a weak base with its conjugate acid) that resists changes in pH when small amounts of an acid or base are added.

Acid Dissociation Constant ($K_a$)

The equilibrium constant for the ionisation of an acid ($K_a = \frac{[H_3O^+][A^-]}{[HA]}$); a large $K_a$ indicates extensive ionisation (strong acid), while a small $K_a$ indicates limited ionisation (weak acid).

Acid-Base Indicator

A weak acid or weak base whose conjugate acid and conjugate base forms have different colours, causing a visible colour change when the pH of the solution equals the $\text{p}K_a$ of the indicator.

Equivalence Point

The point in a titration at which the reacting species have completely reacted in their exact stoichiometric mole ratios, where $[H^+] = [OH^-]$.

End Point

The point in a titration at which an indicator undergoes a visible colour change, indicating that the reaction has reached its observational completion within the indicator's pH range.

Conductometric Titration Curves

Plots of electrical conductance versus the volume of titrant added; strong acid-strong base and strong acid-weak base systems produce well-defined endpoints at the intersection of two lines, whereas weak acid-strong base systems produce poorly defined endpoints beyond the minimum conductance.

Redox Reaction

A reaction involving electron transfer from a reducing agent to an oxidising agent, wherein one substance increases in oxidation number (oxidised) and another decreases in oxidation number (reduced).

Oxidation

The loss of electrons from a chemical species, resulting in an increase in its oxidation number.

Reduction

The gain of electrons by a chemical species, resulting in a decrease in its oxidation number.

Galvanic Cell

An electrochemical cell that converts chemical energy into electrical energy through a spontaneous redox reaction, featuring a negative anode and a positive cathode.

Electrolytic Cell

An electrochemical cell that uses external electrical energy to drive a non-spontaneous redox reaction, converting electrical energy into chemical energy, with a positive anode and a negative cathode.

Anode

The electrode at which oxidation occurs and from which electrons flow into the external circuit.

Cathode

The electrode at which reduction occurs and toward which electrons flow from the external circuit.

Zinc-Copper Galvanic Cell

A galvanic cell generating approximately $1.1\,\text{V}$ from the oxidation of zinc at the anode ($Zn(s) \rightarrow Zn^{2+}(aq) + 2e^-$, redox potential $-0.76\,\text{V}$) and reduction of copper at the cathode ($Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$, redox potential $+0.34\,\text{V}$), connected by an external wire and a salt bridge.

Salt Bridge

A component connecting two half-cells that enables ions to migrate between them to keep electrical charge balanced, with anions moving toward the anode and cations moving toward the cathode.

Standard Hydrogen Electrode

A reference half-cell consisting of a platinum rod submerged in a solution of $H^+(aq)$ with $H_2(g)$ bubbling through under standard conditions, having an assigned potential of $E^\circ = +0.00\,\text{V}$.

Standard Electrode Potential ($E^\circ$)

The potential difference of a reduction half-cell measured relative to the standard hydrogen electrode under standard conditions, which drives electron flow in an external circuit.

Acidic Hydrogen Fuel Cell

A fuel cell operating in acidic conditions where $H_2(g)$ oxidises at the anode ($2H_2(g) \rightarrow 4H^+(aq) + 4e^-$, $E^\circ = +0.00\,\text{V}$) and $O_2(g)$ reduces at the cathode ($O_2(g) + 4H^+(aq) + 4e^- \rightarrow 2H_2O(l)$, $E^\circ = +1.23\,\text{V}$), forming water and generating electricity.

Alkali Fuel Cell

A fuel cell operating in alkaline conditions where $H_2$ is oxidised at the anode ($2H_2(g) + 4OH^-(aq) \rightarrow 4H_2O(l) + 4e^-$, $E^\circ = -0.83\,\text{V}$) and $O_2$ is reduced at the cathode ($O_2(g) + 2H_2O(l) + 4e^- \rightarrow 4OH^-(aq)$, $E^\circ = +0.40\,\text{V}$), commonly utilizing nickel or platinum catalysts.

Homologous Series

A family of organic compounds sharing the same functional group and general formula, whose successive members differ sequentially by a $-CH_2-$ unit and display similar chemical properties.

Saturated Organic Molecule

An organic molecule containing only single carbon-carbon bonds ($C-C$).

Unsaturated Organic Molecule

An organic molecule containing at least one carbon-carbon multiple bond, such as a $C=C$ double bond, allowing addition reactions to take place.

Structural Isomers

Molecules having identical molecular formulas but different structural arrangements, classified into chain isomers, position isomers, and functional group isomers.

Stereoisomers

Isomers sharing the same molecular formula and bonding connectivity, but differing in spatial 3D orientation; they include geometric (cis/trans) and optical isomers.

Low-Density Polyethylene (LDPE)

An addition polymer of ethene that is highly branched, preventing chains from packing closely, resulting in softer and more flexible material with lower density and weaker intermolecular dispersion forces.

High-Density Polyethylene (HDPE)

An addition polymer of ethene made of predominantly linear chains with little branching, allowing tight packing, which produces a strong, rigid material with high density and strong dispersion forces.

Isotactic Polypropene

A polypropene stereoisomer configuration in which all methyl ($-CH_3$) groups are positioned on the same side of the polymer chain, giving the highest intermolecular forces compared to syntactic and atactic forms.

Polytetrafluoroethylene (PTFE)

A chemically inert addition polymer synthesized from tetrafluoroethylene ($F_2C=CF_2$) in the presence of an initiator such as acetyl peroxide, known commercially as Teflon and characterized by exceptionally strong carbon-fluorine bonds.

Nylon 6,6

A synthetic polyamide formed by condensation polymerisation between hexanedioic acid and hexane-1,6-diamine, linked via recurring amide linkages with the release of $(2n - 1)H_2O$.

Polyester

A synthetic polymer formed through a condensation reaction between a dicarboxylic acid and a diol, joined by ester linkages with the elimination of water molecules.

Zwitterion

A dipolar form of an amino acid where the carboxyl group acts as an acid and donates a proton to the amine group, resulting in positive and negative terminal charges while remaining overall electrically neutral.

Isoelectric Point ($pI$)

The pH at which an amino acid possesses a net electric charge of zero; when the buffer pH is greater than $pI$, the amino acid is deprotonated and negatively charged, and when the pH is less than $pI$, it is protonated and positively charged.

Peptide Bond

A covalent amide bond ($-CO-NH-$) formed between the carboxyl group of one amino acid and the amino group of another via a condensation reaction, eliminating a water molecule.

Tripeptide

A molecule consisting of three amino acid units linked in sequence by two peptide bonds, such as three joined glycine units.

Glycosidic Bond

A covalent bond joining carbohydrate monosaccharide units (such as glucose and fructose to form sucrose) through a condensation reaction with the elimination of water.

Haber Process

The industrial synthesis of ammonia ($NH_3$) operating at compromise optimal conditions of $400^{\circ}\text{C}$, $200\,\text{atm}$, and an $Fe_2O_3$ catalyst to balance yield and reaction rate.

Contact Process

The industrial synthesis of sulfuric acid ($H_2SO_4$), which incorporates the reversible oxidation of sulfur dioxide ($2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$, $\Delta H = -196\,\text{kJ}\,\text{mol}^{-1}$) optimised at $400^{\circ}\text{C}$, $1-2\,\text{atm}$, and a $V_2O_5$ catalyst.

Polylactic Acid (PLA)

A biodegradable polymer made from renewable resources, synthesized by dehydrating lactic acid monomers into cyclic lactide molecules, which subsequently polymerise.

Esterification

A reversible condensation reaction between a carboxylic acid and an alcohol in the presence of concentrated sulfuric acid ($H_2SO_4$) to produce an ester and water.