Chemistry Unit 2 Revision Cards

Exothermic

Reactions which give out heat as they proceed

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Endothermic

Reactions which take in heat from environment

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Enthalpy Change

A measure of heat energy given out or taken in when a chemical or physical change occurs at constant pressure

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Standard molar enthalpy of formation

The enthalpy change when one mole of substance is formed from its constituent elements under standard conditions all reactants and products in their standard states

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Standard molar enthalpy of combustion

The enthalpy change when one mole of substance is completely burnt in oxygen under standard conditions, all reactants and products in their standard states

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Heat

Measure of the total energy of all particles present in a given amount of substance

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Temperature

Related to the average kinetic energy of particles in a system

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Calorimeter

An instrument for measuring the heat changes that accompany chemical reactions

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Specific Heat Capacity

The amount of heat needed to raise the temperature of 1g of substance by 1K

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Hess's law

States that the enthalpy change for a chemical reaction is the same whatever route is taken

10 of 105

Enthalpy of elements

In their standard states (states that exist at 298K and 100kPa) are zero

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Bond dissociation enthalpy

The enthalpy chnage required to break a covalent bond with all species in their gaseous state

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Mean bond enthalpy

Average value of the bond dissociation enthalpy for a given type of bond taken from a range of different compounds

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Collision Theory

Most collisions between molecules don't lead to a reaction. They either don't have enough energy or they are the wrong orientation.

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Activation Energy

Minimum energy required to start a reaction (enough to start breaking bonds)

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Catalyst

Substance that can change the rate of reaction without being chemically changed itself, does this by providing a different route for the reaction, usually at a lower activation energy

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Maxwell-Boltzmann distribution

The distribution of energies (and their speeds) of the molecules in a gas or liquid

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Heterogeneous catalyst

Where the catalyst is in a different phase to the reactants - usually a solid catalyst and reactants are liquids/gases

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Homogeneous catalyst

Where catalyst and reactants are in the same phase

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Catalytic converter

Reduces level of polluting gases in exhaust systems. It is a honeycomb, made of ceramic coated with metal catalysts (e.g. platinum)

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Equilibrium Mixture

The mixture of reactants and products formed when a reversible reaction is allowed to proceed in a closed container until no further change occurs (forward and backward reactions are at the same rate)

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Dynamic equilibrium

A situation in which the composition of a reaction mixture doesn't change because both the forward and the backward reactions are proceeding at the same rate

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Closed system

One where reactants and products can't escape

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Reversible reaction

In reversible reactions, as the reactants react with other reactants to form products, the products are reacting with other products to form reactants.

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Le Chatelier's Principle

If a system at equilibrium is disturbed the equilibrium shifts in the direction that tends to reduce the distrubance

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Chemical feedstock

The starting materials in an industrial chemical process

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Redox reaction

Describes reactions in which electrons are transferred from one species to another

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Oxidation

A reaction in which an atom or group of atoms loses electrons

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Oxidising agent

A reagent that oxidises (removes electrons from another species). It is reduced itself.

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Reduction

A reaction in which an atom/group of atoms gains an electron

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Reducing agent

A reagent that reduces (donates electron to another species). It is oxidised

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Half equation

An equation for a redox reaction which considers just one of the species involved and shows explicitly the electrons transferred to/from it

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Spectator Ion

Ions that are unchanged during a chemical reaction - take no part in the reaction

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Oxidation state/number

The number of electrons lost/gained by an atom in a compound compared to uncombined atom. Forms basis of a way of keeping track of redox reactions.

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Halogen

Group 7 elements e.g. F, Cl, Br, I, At

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Diatomic

Molecule which consists of only a bonded pair of electrons

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Displacement reaction

A chemical reaction in which one atom or group of atoms replaces another in a compound

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Disproportionation

Describes a redox reaction in which oxidation number of some atoms of a particular element increases and that of other atoms of the same element decreases

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Chloric (I) acid

HClO, oxidising agent which kills bacteria also a bleach

39 of 105

Sodium chlorate (I)

Used to form chloric acid with water, oxidising agent used in bleach

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Alkaline earth metals

Group 2 elements e.g. Be, Mg, Ca, Sr, Ba, Ra

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Milk of magnesia

Magnesium hydroxide Mg(OH)2, used in indigestion tablets to neutralise excess stomach acid

42 of 105

Barium meal

Barium sulphate, BaSO4 used to outline the gut during xrays as it absorbs them. Not toxic as insoluble.

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Slaked Lime

Calcium Hydroxide Ca(OH)2 used to treat acidic soil

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Ore

Rock containing enough metal to make it economically viable to extract

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Roasting

Process by which sulfide ores are converted to oxides by heating in air

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Acid rain

Rainfall

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Coke

Impure form of carbon often chosen as a reducing agent for the extraction of metals

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Silica

SiO2, major impurity in iron ores

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Haematite

Fe2O3, major iron ore

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Blast furnace

A large vertical furnace for extraction of iron from ore using coke as the fuel. Designed to direct a continuous blast of air through the fuel in order to obtain a high rate of combustion

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Malachite

Copper Ore containing copper carbonate, copper removed by heating, then heated oxide produced with coke

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Electrolysis

The passage of electric current through an electrolyte with subsequent migration of positively and negatively charged ions to the negative and positive electrodes

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Cathode

Negatively charged electrode

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Anode

Positively charged electrode

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Cation

Positively charged ion

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Anion

Negatively charged ion

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Rutile

Ore made largely on titanium (IV) oxide. Converted to titanium (IV) chloride by reacting with coke and chlorine. Titanium then removed by reduction by sodium

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Haloalkane

Organic compound in which halogen atoms have been substituted for hydrogen atoms in an alkane

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Polar Bond

Types of covalent bond between two atoms in which electrons are shared unequally. So one end of the molecule has a slightly positive charge and the other end a slightly negative charge

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Nucleophile

Ion or group of atoms with a negative charge or partially negatively charged area that takes part in an organic reaction by attacking an electron-deficient area in another reactant

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Nucleophile substitution

An organic reaction in which a molecule with a partially positively charged atom is attacked by a nucleophile. Results in the replacement of one of the groups of atoms on the original molecule with the nucleophile.

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Leaving group

In an organic substitution reaction, the leaving group is the atom or group of atoms ejected from the starting material, normally taking an electron with it and forming a negative ion.

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Nitrile

Formed when haloalkanes react with cyanide ions, organic compounds with the general formual RC(triple bond)N

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Elimination

Reaction in which an atom or group of atoms is removed from a reactant

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CFCs

Chlorofluorocarbons, haloalkanes containing both chlorine and fluorine but no hydrogen

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Intiation

Process of generating free radicals which induce a chain reaction

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Propagation

Intermediary step in a chain reaction, where the products of one reaction supply the reactants of the next reaction.

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Termination

Step in a chain reaction in which reactive intermediates are destroyed

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Free radical

Chemical species with an unpaired electron - usually highly reactive

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Free radical substitution

Used to form haloalkanes, one hydrogen atom of alkane is replaced by free radical

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Ozone degradation

Destruction of upper atmospheric layer of ozone gas caused by CFCs

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Alkene

Unsaturated hydrocarbon with general formula CnH2n

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Planar

Shape of molecules around C=C bond, flat with bond angles of roughly 120 degrees

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Stereoisomerism

Have the structural formula but bonds are arranged differently in space

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Geometrical isomer

Also known as E-Z isomerism, a type of stereoisomerism caused when atoms/groups of atoms are attached in different spatial arrangements on either side of a bond

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Electrophile

An electron-deficient atom, ion or molecule that takes part in an organic reaction by attacking areas of high electron density in another reactant

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Electrophilic addition

A reaction in which a C=C bond is saturated and in which the intial reaction is an attack by an electrophile

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Positive inductive effect

Describes the tendency of some atoms or groups of atoms to release electrons via a covalent bond

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Carbocation

An organic ion in which one of the carbon atoms has a positive charge

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Addition polymerisation

Reaction where alkenes join up into long chains called polymers

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Monomer

A molecule which can combine with others to form a polymer

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Repeating unit

Smallest group of atoms that produce the polymer when repeated over and over

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Biodegradable

Capable of being decomposed by biological agents e.g. bacteria

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Mechanical Recycling

Plastics are recycled by washing, sorting and then grinding them into smaller pellets and metling and remoulding them

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Feedstock recycling

Plastics are recyled by heating to a temperature that will break the polymer bonds and produce monomers. These can then be used to make new plastics.

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Alcohol

Organic compound with the general formula of CnH2n+1OH, it is the functional group -OH attached to a hydrocabon chain.

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Primary/ secondary/tertiary alcohol

Carbon attacked to -OH is attached to one/two/three other carbon atoms

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Fermentation

Process used in the production of ethanol from sugars - chemical breakdown of a substance by bacteria/yeast/other microorganisms

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Hydration

Process by which ethanol is made from ethene (water added in the presence of a phosphoric acid catalyst) process of combining with water, usually reversible

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Carbon neutral

An activity which has no net carbon/GHG emissions to the atmosphere

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Biofuel

Fuel derived from a renewable source (living matter e.g. ethanol from fermentation)

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Aldehyde

Organic compound containing functional group -CHO formed by the oxidation of primary alcohols.

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Ketone

Organic compound containing functional group -C=O, formed by oxidation of secondary alcohols

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Carboxylic acid

Organic acid containing carboxyl group (COOH) formed by the complete oxidation of primary alcohols

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Distillation

The action of purifying a liquid by a process of heating and cooling

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Refluxing

The process of boiling a liquid so that any vapour is liquefied and returned to the stock

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Fehling's/Benedict's test

Test to distinguish between ketones and aldehydes. Benedict's reagent is an oxidising agent, when reduced it goes from blue to red ppt. Aldehydes will be oxidised and ketones will not

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Tollen's reagent

Test to distinguish between ketones and aldehydes. Tollen's reagent is an oxidising reagent, it turns from colourless to metallic silver ions. Aldehydes will be oxidised and ketones will not

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Dehydration

Process by which alkenes are formed from alcohols (added to excess H2SO4

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Molecular ion

In mass spec, this is the molecule of the sample which has been ionised by which hasn't broken up during its flight through the instrument.

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Mass Spectrometry

Instrumental method for identifying the chemical constitution of a substance by means of the separation of gaseous ions according to their differing mass and charge.

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Infra-red spectroscopy

Instrumental technique used to identify substances in particular functional groups present in organic compounds by measuring absorption of IR radiation over a range of frequencies, pattern then compared to IR of known substances for identification

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Peaks (on IR)

Dips in the IR graph which represent particular bonds

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Fingerprint region

The area of a IR spec below about 1500 cm-1 caused by complex vibrations of the hole molecule and is characteristic of a particular molecule

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Chemistry Unit 2 Revision Cards

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