Chemistr Unit 4 Definitions

All the definitions needed for AQA Chemistry Unit 4

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Chapter One: Kinetics

Rate of Reaction; is defined as the change in concentration of any reactant or product with unit time.

The Rate Expression  is a mathematical expression showing how the rate of a chemical reaction depends on the concentrations of various species involved.

The Rate Constant is the constant of proportionality in the rate expression.

The Rate Determining Step is the slowest step in the reaction mechanism and governs the rate of the overal reaction.

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Chapter Three: Acids, Bases and Buffers

An Acid is a substance that can donate a proton (H+ ion).

A Base is a substance that can accept a proton.

The Oxonium Ion is an oxygen cation with three bonds (H3O+)

pH is defined as -log10[H+(aq)]

A Strong Acid is one that dissociates completely in dilute aqueous solution.

A Weak Acid is one that dissociates incompletely in dilute aqueous solution.

The Equilivance Point is the point at which sufficient base has been added to just neutralise the acid (or vice-versa)

Buffers are solutions that can resist changes in acidity or alkalinity.

An Acidic Buffer is made from a mixture of a weak acid and a soluble salt of that acid.

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Chapter Four: Nomenclature and Isomerism in Organi

Prefixes are added to the beginning of the root.

Suffixes are added to the end of the root.

Functional Groups are specific groups of atoms within molucules that are responsible for the characteristic chemical reactions of those molecules.

Isomers are compounds with the same molecular formula but a different arrangement of atoms in space.

E-Z Isomerism tells us about the positions of substituents at either side of a carbon-carbon double bond.

Optical Isomers occur when there are four different substituents attached to one carbon atom.

Chiral means 'handed'. A chiral molecule exists in two mirror image forms that are not superimposable.

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Chapter Four: Nomenclature and Isomerism in Organi

Enantiomers are a pair of non-superimposable mirror image isomers.

The Chiral Centre is an atom to which four different atoms or groups are bonded. The presence of such an atom causes the parent molecule to exist as a pair of non-superimposable mirror images.

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Chapter Five: Compounds Containing The Carbonyl Gr

The Carbonyl Group is the C=O present in both aldehydes and ketones.

A Nucleophilic Addition reaction is an addition reaction where in a chemical compound the double bond is removed by the addition of a nucleophile.

A Nucleophile is a negatively charged molecule or atom with a lone pair of electrons.

Oxidation is the loss of one or more electrons to increase the oxidation number of the atom.

Fehling's Solution is made from a mixture of two solutions Fehling's A (Cu2+ ions) and Fehling's B which contains an alkali and a complex agent. It is used to distinguish between aldehydes and ketones.

Tollens' Reagent comtains the complex ion [Ag(NH3)2+] formed when aqueous ammonia is added to aqueous silver nitrate. It is also used to distinguish between aldehydes and ketones.

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Chapter Five: Compounds Containing the Carbonyl Gr

Reduction is the gain of one or more electrons to increase the oxidation number of the atom.

Carboxylic Acids have the functional group C=OOH or COOH and can only be at the end of a carbon chain.

Esters have the functional groupRC=OR' are derived from carboxylic acids, where the hydrogen group is replaced with a hydrocarbon group. the double bond stay.

Delocalisation describes the process by which electrons are spread over several atoms and help bond them together.

Fatty Acids are long chain carboxylic acids.

A Triglyceride is an ester formed between glycerol (propane-1,2,3-triol) and three fatty acid molecules.

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Chapter Five: Compounds Containing the Carbonyl Gr

Acylation is the process by which the acyl group is introduced into another molecule.

An Acid Derivative is an organic compound related to a carboxylic acid of formula RCOZ.

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Chapter Six: Aromatic Chemistry

An Arene is a hydrocarbon based on benzene (C6H6).

Resonance

Resonance Hybrids

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