Chemistry Defs

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Dipole-Dipole forces

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Forces between two polar molecules

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Induced dipole-dipole forces (London forces)

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Forces between non-polar molecules

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Hydrogen bonding

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Forces between molecules in which hydrogen is covalently bonded to nitrogen, oxygen or flourine

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Boiling point

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The temperature at which the vapour pressure equals the atmospheric pressure

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Melting point

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The temperature at which the solid and the liquid phase of a substance are at equilibrium

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Vapour pressure

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The pressure exerted by a vapour at equilibrium with its liquid in a closed system

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Organic molecules

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Molecules containing carbon atoms

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Molecular formula

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Chemical formula which indicates the type of atoms and the correct number of each in a molecule

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Structural formula

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Shows which atoms are attached to which within a molecule

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Condensed formula

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Shows the way in which atoms are bonded together in the molecule but does not show all bond lines

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Hydrocarbon

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Organic compounds that consist of hydrogen and carbon only

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Homologous series

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Series of organic compounds that can be described by the same general formula

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Saturated compound

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

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Unsaturated compounds

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

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Functional group

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A bond, atom or group of atoms that determine the physical and chemical properties of a group of organic compounds

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Structural isomer

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Organic molecules with the same molecular formula but different structural formulae

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Chain isomer

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Organic molecules with the same molecular formula but different types of chains

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Positional isomer

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Organic molecules with the same molecular formulate but different positions of the side chain

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Functional isomer

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Organic molecules with the same molecular molecule but different functional group

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Macromolecule

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A molecule that consists of a large number of atoms

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Monomer

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

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Polymer

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

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Polymerisation

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

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Percentage purity

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Mass of pure substance ÷ mass of impure substance × 100

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Percentage yield

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Made of product produced ÷ maximum theoretical mass of product × 100

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Heat of reaction △H

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Energy absorbed or released in a chemical reaction

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Exothermic reaction

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Reactions that release energy

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Endothermic reactions

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Reactions that absorb energy

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Activation energy

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Minimum energy needed for a reaction to take place

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Activated complex

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The unstable transition state from reactants to products

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Reaction rate (Rate=△c÷△t)

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The change in concentration of reactants or products per unit time

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Collision theory

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

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(Positive) Catalyst

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

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Open system

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Continuously interacting with the environment

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Closed system

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Isolation from its surroundings

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Reversible

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When products can be converted back to reactants

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Chemical equilibrium

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A dynamic equilibrium when the rate of the forward reaction equals the rate of the reverse reaction

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Le Chatelier's principle

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When the equilibrium in a closed system is disturbed, the system will reinstate a new equilibrium by favouring the reaction that will oppose the disturbance

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Acid (Arrhenius theory)

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Substance that produced hydrogen ions in water

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Base (Arrhenius theory)

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Substance that produces hydroxide in water

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Acid (Lowry-Brønsted theory)

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A proton donor

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Base (Lowry-Brønsted theory)

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Proton acceptor

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Weak acids examples

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Ethanoic acid, oxalic acid

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Strong acid examples

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Hydrochloric acid, sulphuric acid, nitric acid

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Weak base examples

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Ammonia, Calcium carbonate, potassium carbonate, sodium hydrogen carbonate

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Amphiprotic

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A substance that can act as either an acid or base

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Equivalence point of a titration

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

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pH scale

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A scale of numbers from 0-14 used to express the hydrogen ion concentration

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Auto-ionisation of water

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The reaction if water with itself to form H³O+ and OH- ions

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Galvanic cell

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A cell in which chemical energy is converted into electrical energy

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Electrolytic cell

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A cell in which electrical energy is converted into chemical energy

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Electrolyte

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A substance that dissolves in water to give a solution that conducts electricity

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Eutrophication

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The process by which an ecosystem becomes enriched with inorganic plant nutrients resulting in excessive plant algae growth