Physical Sciences: Chemistry Terms and Definitions

Comprehensive chemistry vocabulary flashcards covering general chemistry, organic reactions, intermolecular forces, reaction kinetics, chemical equilibrium, acids and bases, and electrochemistry definitions.

Empirical formula

The simplest positive integer ratio of atoms present in a compound.

Molecular formula

A chemical formula that indicates the element and numbers of each of the atoms in a molecule.

Percentage yield

The amount of substance produced during a reaction given as a percentage.

Percentage composition

The composition of the elements in a molecule given as a percentage.

Dipole-dipole forces

Forces between two polar molecules.

Induced dipole / London forces

Forces between non-polar molecules.

Hydrogen bonding

Forces between molecules in which hydrogen is covalently bonded to nitrogen, oxygen or fluorine - a special case of dipole-dipole forces.

Intermolecular forces

Forces between individual particles of a substance.

Interatomic forces / chemical bonds (intramolecular forces)

Forces/bonds between atoms within a molecule or compound.

Boiling point

The temperature at which the vapour pressure of a substance equals atmospheric pressure. The stronger the intermolecular forces, the higher the boiling point.

Melting point

The temperature at which the solid and liquid phases of a substance are at equilibrium. The stronger the intermolecular forces, the higher the melting point.

Vapour pressure

The pressure exerted by a vapour at equilibrium with its liquid in a closed system. The stronger the intermolecular forces, the lower the vapour pressure.

Organic molecules

Molecules containing carbon atoms.

Structural formula

A structural formula of a compound shows which atoms are attached to which within the molecule. Atoms are represented by their chemical symbols and lines are used to represent ALL the bonds that hold the atoms together.

Condensed structural formula

This notation shows the way in which atoms are bonded together in the molecule, but DOES NOT SHOW ALL bond lines.

Hydrocarbon

Organic compounds that consist of hydrogen and carbon only.

Homologous series

A series of organic compounds that can be described by the same general formula OR in which one member differs from the next with a $CH_2$ group.

Saturated compounds

Compounds in which there are no multiple bonds between C atoms in their hydrocarbon chains.

Unsaturated compounds

Compounds with one or more multiple bonds between C atoms in their hydrocarbon chains.

Functional group

A bond or an atom or a group of atoms that determine(s) the physical and chemical properties of a group of organic compounds.

Structural isomer

Organic molecules with the same molecular formula, but different structural formulae.

Chain isomer

Same molecular formula, but different types of chains, e.g. butane and 2-methylpropane.

Positional isomers

Same molecular formula, but different positions of the side chain, substituents or functional groups on the parent chain, e.g. 1-chloropropane and 2-chloropropane or but-2-ene and but-1-ene.

Functional isomers

Same molecular formula, but different functional groups, e.g. methyl methanoate and ethanoic acid.

Hydrohalogenation

The addition of a hydrogen halide to an alkene.

Halogenation

The reaction of a halogen ($Br_2$, $Cl_2$) with a compound.

Hydration

The addition of water to a compound.

Hydrogenation

The addition of hydrogen to an alkene.

Dehydrohalogenation of haloalkanes

The elimination of hydrogen and a halogen from a haloalkane.

Dehydration of alcohols

Elimination of water from an alcohol.

Cracking of alkanes

The chemical process in which longer chain hydrocarbon molecules are broken down to shorter more useful molecules.

Hydrolysis – organic chemistry

The reaction of a compound with water.

Macromolecule

A molecule that consists of a large number of atoms.

Polymer

A large molecule composed of smaller monomer units covalently bonded to each other in a repeating pattern.

Monomer

Small organic molecules that can be covalently bonded to each other in a repeating pattern.

Polymerisation

A chemical reaction in which monomer molecules join to form a polymer.

Addition polymer

A polymer formed when monomers (usually containing a double bond) combine through an addition reaction.

Condensation polymerisation

Molecules of two monomers with different functional groups undergo condensation reactions with the loss of small molecules, usually water.

Condensation polymer

A polymer formed by two monomers with different functional groups that are linked together in a condensation reaction in which a small molecule, usually water, is lost.

Heat of reaction ($\Delta H$)

The energy absorbed or released in a chemical reaction.

Exothermic reaction

Reactions that release energy.

Endothermic reaction

Reactions that absorb energy.

Activation energy

The minimum energy needed for a reaction to take place.

Activated complex

The unstable transition state from reactants to products.

Reaction rate

The change in concentration of reactants or products per unit time.

Collision theory

A model that explains reaction rate as the result of particles colliding with a certain minimum energy to form products.

Catalyst

A substance that increases the rate of a chemical reaction without itself undergoing a permanent change.

Open system

An open system continuously interacts with its environment.

Closed system

A closed system is isolated from its surroundings.

Reversible reaction

A reaction is reversible when products can be converted back to reactants and vice versa.

Chemical equilibrium

It is a dynamic equilibrium when the rate of the forward reaction equals the rate of the reverse reaction.

Le Chatelier's principle

When the equilibrium in a closed system is disturbed, the system will re-instate a new equilibrium by favouring the reaction that will oppose the disturbance.

Arrhenius theory

Acids produce hydrogen ions ($H^+$ / $H_3O^+$ / hydronium ions) in aqueous solution. Bases produce hydroxide ions ($OH^-$) in aqueous solution.

Lowry-Brønsted theory

An acid is a proton ($H^+$ ion) donor. A base is a proton ($H^+$ ion) acceptor.

Strong acids

Ionise completely in water to form a high concentration of $H_3O^+$ ions.

Weak acids

Ionise incompletely in water to form a low concentration of $H_3O^+$ ions.

Strong bases

Dissociate completely in water to form a high concentration of $OH^-$ ions.

Weak bases

Dissociate/ionise incompletely in water to form a low concentration of $OH^-$ ions.

Concentrated acids/bases

Contain a large amount (number of moles) of acid/base in proportion to the volume of water.

Dilute acids/bases

Contain a small amount (number of moles) of acid/base in proportion to the volume of water.

Ampholyte

A substance that can act as either acid or base. Water is a good example of an ampholyte substance.

Hydrolysis – acid-base chemistry

The reaction of a salt with water.

Equivalence point

The point at which the acid/base has completely reacted with the base/acid.

Endpoint

The point where the indicator changes colour.

pH scale

A scale of numbers from $0$ to $14$ used to express the acidity or alkalinity of a solution.

$$K_w$$

The equilibrium constant for the ionisation of water or the ion product of water or the ionisation constant of water, i.e. $K_w = [H_3O^+][OH^-] = 1 \times 10^{-14}$ at $298\,\text{K}$.

Auto-ionisation of water

The reaction of water with itself to form $H_3O^+$ ions and $OH^-$ ions.

Galvanic cell

A cell in which chemical energy is converted to electrical energy.

Oxidation – electron transfer

A loss of electrons.

Reduction – electron transfer

A gain of electrons.

Oxidation – oxidation number

An increase in oxidation number.

Reduction – oxidation number

A decrease in oxidation number.

Oxidising agent

A substance that is reduced/gains electrons.

Reducing agent

A substance that is oxidised/loses electrons.

Anode

The electrode where oxidation takes place.

Cathode

The electrode where reduction takes place.

Electrolyte

A substance of which the aqueous solution contains ions OR a substance that dissolves in water to give a solution that conducts electricity.

Electrolytic cell

A cell in which electrical energy is converted into chemical energy.

Electrolysis

The chemical process in which electrical energy is converted to chemical energy OR the use of electrical energy to produce a chemical change.