A-Level Chemistry: Bonding, Thermochemistry, and Organic Compounds

Vocabulary-style practice flashcards covering thermochemistry, chemical kinetics, green chemistry, and organic chemistry principles as detailed in the lecture notes.

Enthalpy change

The name given to the amount of heat given out or absorbed in a reaction carried out at constant pressure.

Exothermic reactions

Reactions that have negative $\Delta H$ values.

Endothermic reactions

Reactions that have positive $\Delta H$ values.

Standard conditions

Conditions used to compare enthalpy values: all substances in standard states, temperature of $298\,K$ ($25^\circ C$), and pressure of $1\,atm$ ($101\,000\,Pa$).

Standard enthalpy change of formation, $\Delta_fH^\theta$

The enthalpy change when $1\,mol$ of a compound forms from its constituent elements in their standard states under standard conditions.

Standard enthalpy change of combustion, $\Delta_cH^\theta$

The enthalpy change when $1\,mol$ of a substance is completely combusted in oxygen under standard conditions.

Hess's law

States that the total enthalpy change for a reaction is independent of the route taken from the reactants to the products.

Bond enthalpy

The enthalpy needed to break $1\,mol$ of the bond to give separated atoms with everything being in the gaseous state.

Average bond enthalpy

The average value of the enthalpy required to break a given type of covalent bond in the molecules of a gaseous species.

Calorimeter

An insulated container used to measure the heat transferred to surroundings during a chemical reaction.

Specific heat capacity ($c$)

The amount of heat required to raise the temperature of a substance, given as $4.18\,J\,g^{-1}\,K^{-1}$ for solutions.

Activation energy, $E_a$

The minimum energy needed for a collision between reacting molecules to be effective and for a chemical reaction to take place.

Collision theory

A theory used to explain how factors affect rates of reaction, stating that molecules must collide in the correct orientation and with sufficient energy to react.

Boltzmann energy distribution curve

A diagram used to show the distribution of molecular energies in a gas and how it changes with temperature.

Catalyst

A substance that increases the rate of a chemical reaction without being used up by providing a different reaction pathway with a lower activation energy.

Homogeneous catalyst

A catalyst that is in the same phase (e.g., liquid or solution) as the reactants.

Heterogeneous catalyst

A catalyst that is in a different state from the reactants, such as iron in the Haber process.

Carbon neutral

A process, such as burning plant-derived biomass, where the carbon dioxide generated is compensated for by the carbon dioxide absorbed during photosynthesis.

Green Chemistry

The practice of making chemicals and products with minimal environmental impact, using renewable materials, high atom economy, and biodegradable products.

Enzymes

Exceptionally efficient biological catalysts that usually catalyse specific reactions and work best close to body temperature.

Functional group

The atom or group of atoms in a compound that gives the compound its characteristic properties.

Homologous series

A family of compounds that have the same functional group and general formula, differing from their neighbor by one $CH_2$ unit.

Hydrocarbon

A compound containing hydrogen and carbon only.

Structural isomerism

Compounds with the same molecular formula but a different structural formula.

Chain isomerism

A form of structural isomerism where the carbon chain is arranged differently, such as through branching.

Position isomerism

A form of structural isomerism where the functional group is in a different position in the molecule.

Functional group isomerism

A form of structural isomerism where the molecular formula is the same but the functional group is different, such as in aldehydes and ketones.

$E-Z$ isomerism

A type of stereoisomerism occurring in alkenes because there is restricted rotation about the $C=C$ double bond.

Sigma ($\sigma$) bond

A covalent bond formed by the end-on overlap of two orbitals, resulting in the highest electron density between the nuclei.

Pi ($\pi$) bond

A covalent bond formed when two p orbitals overlap side-on, above and below the plane of the molecule.

Electrophilic addition

A reaction mechanism where an electrophile attacks the high electron density of a $C=C$ double bond, common in alkenes.

Nucleophile

A species that can donate an electron pair to a partial positive charge ($\delta+$); examples include $H_2O$, $NH_3$, and $OH^-$.

Reflux

A process of heating a reaction mixture with a condenser to cool vapours so they condense and run back into the flask, preventing the loss of volatile chemicals.

Elimination reaction

A reaction where a halogenoalkane reacts with an ethanolic base to form an alkene, water, and a halide ion.

Biofuels

Renewable fuels produced from living organisms, such as bioethanol from sugars and biodiesel from oils and fats.

Esterification

The reaction between a carboxylic acid and an alcohol, catalysed by concentrated sulfuric acid, to produce an ester and water.