Mocks Science 2 definitions

Boiling point

The temperature at which the vapour pressure of a substance equals atmospheric pressure.

Melting point

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

Vapour pressure

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

Heat of reaction

The energy absorbed or released in a chemical reaction.

Exothermic reactions

Reactions that release energy.

Endothermic reactions

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.

Collision theory

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

Reaction rate

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

Catalyst

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

State 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.

Open system

An open system continuously interacts with its environment, while a closed system is isolated from its surroundings.

A reversible reaction

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

Chemical Equilibrium

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

Arrhenius theory acid

Acids produce hydrogen ions (H+/H3O+/hydronium ions) in aqueous solution.

Arrhenius theory base

Bases produce hydroxide ions (OH-) in aqueous solution.

Lowry-Brønsted theory acid

An acid is a proton (H+ ion) donor.

Lowry-Brønsted theory base

A base is a proton (H+ ion) acceptor.

Hydrolysis

The reaction of a salt with water.

Equivalence point of a titration

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

Endpoint of a titration

The point where the indicator changes colour

Strong acids

Strong acids ionise completely in water to form a high concentration of H3O+ ions

Weak acids

Weak acids ionise incompletely in water to form a low concentration of H3O+ ions.

Strong bases

Strong bases dissociate completely in water to form a high concentration of OH- ions.

Weak bases

Weak bases dissociate/ionise incompletely in water to form a low concentration of OH- ions.

Concentrated acids

Concentrated acids contain a large amount (number of moles) of acid in proportion to the volume of water.

Concentrated bases

Concentrated bases contain a large amount (number of moles) of base in proportion to the volume of water

Dilute acids

Dilute acids contain a small amount (number of moles) of acid in proportion to the volume of water.

Endpoint of a titration

The endpoint of a titration is the point where the indicator changes colour.

The pH scale

The pH scale is a scale of numbers from 0 to 14 used to express the acidity or alkalinity of a solution.

Auto-ionisation of water

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

Dilute bases

Dilute bases contain a small amount (number of moles) of base in proportion to the volume of water.

Hydrolysis

The reaction of a salt with water.

Kw

The equilibrium constant for the ionisation of water

Ampholyte

A substance that can act as either acid or base.

Galvanic cell

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

Oxidation in terms of electron transfer

Oxidation is a loss of electrons

Reduction in terms of electron transfer

Reduction is a gain of electrons.

Oxidation in terms of oxidation numbers

an increase in oxidation number

Reduction in terms of oxidation numbers

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

Electrolysis

The chemical process in which electrical energy is converted to chemical energy

Electrolytic cell

A cell in which electrical energy is converted into chemical energy

Organic molecules

Molecules containing carbon atoms.

Molecular formula

A chemical formula that indicates the type of atoms and the correct number of each in a molecule.

Structural formula

A structural formula of a compound shows which atoms are attached to which within the molecule.

Condensed structural formula

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

Hydrocarbons

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 CH2 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 isomers

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

Chain isomers

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

Positional isomers

Organic molecules with the same molecular formula, but different positions of the side chain, substituents or functional groups on the parent chain.

Functional isomers

Organic molecules with the same molecular formula, but different functional groups.

Hydrohalogenation

The addition of a hydrogen halide to an alkene.

Halogenation

The reaction of a halogen with a compound

Hydration

The addition of water to a compound

Hydrogenation

The addition of hydrogen to an alkene.