Students should: Introduction This unit introduces more of the principles that underpin chemistry and looks at the applications of these principles and those that have been developed in Unit 1. Wherever possible, candidates should carry out experimental work to illustrate the theoretical principles included in this unit. A knowledge of the Chemistry in Unit 1 is assumed in this unit.

3.2.1 Energetics

Enthalpy change (ΔH)

• know that reactions can be endothermic or exothermic
• understand that enthalpy change (ΔH) is the heat energy change measured under conditions of constant pressure
• know that standard enthalpy changes refer to standard conditions, i.e. 100 kPa and a stated temperature (e.g. ΔH298)
• be able to recall the definition of standard enthalpies of combustion (ΔHc ) and formation (ΔHf )

Calorimetry

• be able to calculate the enthalpy change from the heat change in a reaction using the equation q = mc ΔT

Simple applications of Hess's Law

• know Hess's Law and be able to use it to perform simple calculations, for example calculating enthalpy changes for reactions from enthalpies of combustion or enthalpies of formation

Bond enthalpies

• be able to determine mean bond enthalpies from given data
• be able to use mean bond enthalpies to calculate a value of ΔH for simple reactions

3.2.2 Kinetics

Collision theory

• understand that reactions can only occur when collisions take place between particles having Sufficient energy
• be able to define the term activation energy and understand its signifi cance
• understand that most collisions do not lead to reaction

Maxwell.Boltzmann distribution

• have a qualitative understanding of the Maxwell.Boltzmann distribution of molecular energies in gases
• be able to draw and interpret distribution curves for different temperatures

Effect of temperature on reaction rate

• understand the qualitative effect of temperature changes on the rate of reaction
• understand how small temperature increases can lead to a large increase in rate

Effect of concentration

• understand the qualitative effect of changes in concentration on rate of reaction

Catalysts

• know the meaning of the term catalyst
• understand that catalysts work by providing an alternative reaction route of lower activation energy

3.2.3 Equilibria

The dynamic nature of equilibria

• know that many chemical reactions are reversible
• understand that for a reaction in equilibrium, although the concentrations of reactants and products remain constant, both forward and reverse reactions are still proceeding at equal rates

Qualitative effects of changes of pressure, temperature and concentration on a system in equilibrium

• be able to use Le Chatelier's principle to predict the effects of changes in temperature, pressure and concentration on the position of equilibrium in homogeneous reactions
• know that a catalyst does not affect the position of equilibrium

Importance of equilibria in industrial processes

• be able to apply these concepts to given chemical processes
• be able to predict qualitatively the effect of temperature on the position of equilibrium from the sign of ΔH for the forward reaction
• understand why a compromise temperature and pressure may be used
• know about the hydration of ethene to form ethanol and the reaction of carbon monoxide with hydrogen to form methanol as important industrial examples where these principles can be applied
• know the importance of these alcohols as liquid fuels

3.2.4 Redox Reactions

Oxidation and reduction know that oxidation is the process of electron loss

• know that oxidising agents are electron acceptors
• know that reduction is the process of electron gain
• know that reducing agents are electron donors

Oxidation states

• know and be able to apply the rules for assigning oxidation states in order to work out the oxidation state of an element in a compound from its formula
• understand oxidation and reduction reactions of s and p block elements

Redox equations

• be able to write half-equations identifying the oxidation and reduction processes in redox reactions when the reactants and products are specified
• be able to combine half-equations to give an overall redox equation

3.2.5 Group 7(17), the Halogens

Trends in physical properties

• understand the trends in electronegativity and boiling point of the halogens

Trends in the oxidising abilities of the halogens

• understand that the ability of the halogens (from fluorine to iodine) to oxidise decreases down the group (e.g. the displacement reactions with halide ions in aqueous solution)

Trends in the reducing abilities of the halide ions

• understand the trend in reducing ability of the halide ions
• know the different products formed by reaction of NaX and H2SO4

Identification of halide ions using silver nitrate

• understand why acidified silver nitrate solution is used as a
• reagent to identify and distinguish between F-, Cl-, Br- and I-
• know the trend in solubility of the silver halides in ammonia

Uses of chlorine and chlorate(I)

• know the reactions of chlorine with water and the use of chlorine in water treatment
• appreciate that the benefits to health of water treatment by chlorine outweigh its toxic effects
• know the reaction of chlorine with cold, dilute, aqueous NaOH and the uses of the solutions formed

3.2.6 Group 2, the Alkaline Earth Metals

Trends in physical properties

• understand the trends in atomic radius, first ionisation energy and melting point of the elements Mg . Ba

Trends in chemical properties

• know the reactions of the elements Mg . Ba with water and recognise the trend
• know the relative solubilities of the hydroxides of the elements Mg . Ba and that Mg(OH)2 is sparingly soluble
• know the use of Mg(OH)2 in medicine and of Ca(OH)2 in agriculture
• know the relative solubilities of the sulfates of the elements Mg . Ba
• understand why acidified BaCl2 solution is used as a reagent to test for sulfate ions
• know the use of BaSO4 in medicine

3.2.7 Extraction of Metals

Principles of metal extraction

• know that metals are found in ores, usually as oxides or sulfides and that sulfide ores are usually converted into oxides by roasting in air
• understand the environmental problems associated with the conversion of sulfi des into oxides and also that the sulfur dioxide produced can be used to manufacture sulfuric acid
• understand that extraction of metals involves reduction
• understand that carbon and carbon monoxide are cheap and effective reducing agents that are used in the extraction of iron, manganese and copper (reduction equations and conditions only)
• know why carbon reduction is not used for extraction of titanium, aluminium and tungsten
• understand how aluminium is manufactured from purifi ed bauxite (energy considerations, electrode equations and conditions only)
• understand how titanium is extracted from TiO2 via TiCl4 (equations and conditions only: either Na or Mg as a reducing agent)
• understand how tungsten is extracted from WO3 by reduction with hydrogen (equation, conditions and risks only)

Environmental aspects of metal extraction

• understand the environmental and economic advantages and disadvantages of recycling scrap metals compared with the extraction of metals
• understand the environmental advantages of using scrap iron to extract copper from aqueous solutions compared with the high-temperature carbon reduction of copper oxide
• know that the usual source of such aqueous solutions is low grade ore

3.2.8 Haloalkanes

Synthesis of chloroalkanes

• understand the reaction mechanism of methane with chlorine as a free-radical substitution reaction in terms of initiation, propagation and termination steps
• know that chloroalkanes and chlorofluoroalkanes can be used as solvents
• understand that ozone, formed naturally in the upper atmosphere is benefi cial
• be able to use equations such as the following to explain why chlorine atoms catalyse the decomposition of ozone and contribute to the formation of a hole in the ozone layer Cl. + O3 ¨ ClO. + O2 and ClO. + O3 ¨ 2O2 + Cl.
• know that chlorine atoms are formed in the upper atmosphere when energy from ultra-violet radiation causes C.Cl bonds in chlorofluorocarbons (CFCs) to break
• appreciate that legislation to ban the use of CFCs was supported by chemists and that they have now developed alternative chlorine-free compounds

Nucleophilic substitution

• understand that haloalkanes contain polar bonds
• understand that haloalkanes are susceptible to nucleophilic attack, limited to OH-, CN-, and NH3
• understand the mechanism of nucleophilic substitution in primary haloalkanes
• understand that the carbon.halogen bond enthalpy influences the rate of hydrolysis
• appreciate the usefulness of these reactions in organic synthesis

Elimination

• understand concurrent substitution and elimination (including mechanisms) in the reaction of a haloalkane (e.g. 2- bromopropane with potassium hydroxide) and the role of the reagent as both nucleophile and base
• appreciate the usefulness of this reaction in organic synthesis

3.2.9 Alkenes

Alkenes: structure, bonding mand reactivity

• know that alkenes are unsaturated hydrocarbons
• know that bonding in alkenes involves a double covalent bond
• know that the arrangement >C=C< is planar
• know that the alkenes can exhibit E-Z stereoisomerism
• be able to draw the structures of E and Z isomers
• understand that E-Z isomers exist due to restricted rotation about the C=C bond
• understand that the double bond in an alkene is a centre of high electron density

Addition reactions of alkenes

• understand the mechanism of electrophilic addition of alkenes with HBr, H2SO4 and Br2
• know that bromine can be used to test for unsaturation
• be able to predict the products of addition to unsymmetrical alkenes by reference to the relative stabilities of primary, secondary and tertiary carbocation intermediates
• understand that alcohols are produced industrially by hydration of alkenes in the presence of an acid catalyst.
• know the typical conditions for the industrial production of ethanol from ethene

Polymerisation of alkenes

• know how addition polymers are formed from alkenes
• recognise that poly(alkenes) like alkanes are unreactive
• be able to recognise the repeating unit in a poly(alkene)
• know some typical uses of poly(ethene) and poly(propene) and know that poly(propene) is recycled

3.2.10 Alcohols

Nomenclature

• be able to apply IUPAC rules for nomenclature to alcohols, aldehydes, ketones and carboxylic acids limited to chains with up to 6 carbon atoms

Ethanol production

• know how ethanol is produced industrially by fermentation
• know the conditions for this reaction and understand the economic and environmental advantages and disadvantages of this process compared with the industrial production from ethene
• understand the meaning of the term biofuel
• know that the term carbon neutral refers to ean activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere'
• appreciate the extent to which ethanol, produced by fermentation, can be considered to be a carbon-neutral biofuel

Classifi cation and reactions

• understand that alcohols can be classified as primary, secondary or tertiary
• understand that tertiary alcohols are not easily oxidised
• understand that primary alcohols can be oxidised to aldehydes and carboxylic acids and that secondary alcohols can be oxidised to ketones by a suitable oxidising agent such as acidifi ed potassium dichromate(VI) (equations showing [O] as oxidant are acceptable)
• be able to use a simple chemical test to distinguish between aldehydes and ketones (e.g. Fehling's solution or Tollens' reagent)

Elimination

• know that alkenes can be formed from alcohols by acid catalysed elimination reactions (mechanism not required)
• appreciate that this method provides a possible route to polymers without using monomers derived from oil

3.2.11 Analytical Techniques

Mass spectrometry

• understand that high resolution mass spectrometry can be used to determine the molecular formula of a compound from the accurate mass of the molecular ion

Infrared spectroscopy

• understand that certain groups in a molecule absorb infrared radiation at characteristic frequencies
• understand that efingerprinting allows identification of a molecule by comparison of spectra
• be able to use spectra to identify particular functional groups and to identify impurities, limited to data presented in wavenumber form
• understand the link between absorption of infrared radiation by bonds in CO2, methane and water vapour and global warming