5 Energy from Chemicals

O Level - Pure Chemistry

(a) describe the meaning of enthalpy change in terms of exothermic (ΔH negative) and endothermic (ΔH positive) reactions
(b) represent energy changes by energy profile diagrams, including reaction enthalpy changes and activation energies (see 6.1(c),6.1(d))
(c) describe bond breaking as an endothermic process and bond making as an exothermic process
(d) explain overall enthalpy changes in terms of the energy changes associated with the breaking and making of covalent bonds
(e) describe hydrogen, derived from water or hydrocarbons, as a potential fuel, reacting with oxygen to generate electricity directly in a fuel cell (details of the construction and operation of a fuel cell are not required)

O Level - Combined Chemistry

(a) describe the term exothermic as a process or chemical reaction which transfers energy, often in the form of heat, to the surroundings and may be detected by an increase in temperature,
e.g. the reaction between sodium hydroxide and hydrochloric acid
(b) describe the term endothermic as a process or chemical reaction which takes in energy, often in the form of heat, from the surroundings and may be detected by a decrease in temperature,
e.g. the dissolving of ammonium nitrate in water

- Syllabuses from SEAB

This section is not covered in the N(A) Level (Combined Chemistry) syllabus.

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4 Electrolysis

O Level - Pure Chemistry

(a) describe electrolysis as the conduction of electricity by an ionic compound (an electrolyte), when molten or dissolved in water, leading to the decomposition of the electrolyte
(b) describe electrolysis as evidence for the existence of ions which are held in a lattice when solid but which are free to move when molten or in solution
(c) describe, in terms of the mobility of ions present and the electrode products, the electrolysis of molten sodium chloride, using inert electrodes
(d) predict the likely products of the electrolysis of a molten binary compound
(e) apply the idea of selective discharge based on
(i) cations: linked to the reactivity series (see 9.2)
(ii) anions: halides, hydroxides and sulfates (e.g. aqueous copper(II) sulfate and dilute sodium chloride solution (as essentially the electrolysis of water))
(iii) concentration effects (as in the electrolysis of concentrated and dilute aqueous sodium chloride)
(In all cases above, inert electrodes are used.)
(f) predict the likely products of the electrolysis of an aqueous electrolyte, given relevant information
(g) construct ionic equations for the reactions occurring at the electrodes during the electrolysis, given relevant information
(h) describe the electrolysis of aqueous copper(II) sulfate with copper electrodes as a means of purifying copper (no technical details are required)
(i) describe the electroplating of metals, e.g. copper plating, and state one use of electroplating
(j) describe the production of electrical energy from simple cells (i.e. two electrodes in an electrolyte) linked to the reactivity series (see 9.2) and redox reactions (in terms of electron transfer)

- Syllabus from SEAB

This section is covered only in the O Level (Pure Chemistry) syllabus.

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3 Formulae, Stoichiometry and the Mole Concept

O Level - Pure Chemistry

(a) state the symbols of the elements and formulae of the compounds mentioned in the syllabus
(b) deduce the formulae of simple compounds from the relative numbers of atoms present and vice versa
(c) deduce the formulae of ionic compounds from the charges on the ions present and vice versa
(d) interpret chemical equations with state symbols
(e) construct chemical equations, with state symbols, including ionic equations
(f) define relative atomic mass, Ar
(g) define relative molecular mass, Mr, and calculate relative molecular mass (and relative formula mass) as the sum of relative atomic masses
(h) calculate the percentage mass of an element in a compound when given appropriate information
(i) calculate empirical and molecular formulae from relevant data
(j) calculate stoichiometric reacting masses and volumes of gases (one mole of gas occupies 24 dm3 at room temperature and pressure); calculations involving the idea of limiting reactants may be set
(The gas laws and the calculations of gaseous volumes at different temperatures and pressures are not required.)
(k) apply the concept of solution concentration (in mol/dm3or g/dm3) to process the results of volumetric experiments and to solve simple problems
(Appropriate guidance will be provided where unfamiliar reactions are involved.)
(l) calculate % yield and % purity

O Level - Combined Chemistry

(a) state the symbols of the elements and formulae of the compounds mentioned in the syllabus
(b) deduce the formulae of simple compounds from the relative numbers of atoms present and vice versa
(c) deduce the formulae of ionic compounds from the charges on the ions present and vice versa
(d) interpret chemical equations with state symbols
(e) construct chemical equations, with state symbols, including ionic equations
(f) define relative atomic mass, Ar
(g) define relative molecular mass, Mr, and calculate relative molecular mass (and relative formula mass) as the sum of relative atomic masses
(h) calculate stoichiometric reacting masses and volumes of gases (one mole of gas occupies 24 dm3 at room temperature and pressure); calculations involving the idea of limiting reactants may be set
(The gas laws and the calculations of gaseous volumes at different temperatures and pressures are not required.)
(i) apply the concept of solution concentration (in mol/dm3 or g/dm3) to process the results of volumetric experiments and to solve simple problems
(Appropriate guidance will be provided where unfamiliar reactions such as redox are involved.
Calculations on % yield and % purity are not required.)

N(A) Level - Combined Chemistry

(a) state the symbols of the elements and formulae of the compounds mentioned in the syllabus
(b) deduce the formulae of simple compounds from the relative numbers of atoms present and vice versa
(c) deduce the formulae of ionic compounds from the charges on the ions present and vice versa
(d) interpret chemical equations with state symbols
(e) construct chemical equations, with state symbols, including ionic equations
(f) define relative atomic mass, Ar
(g) define relative molecular mass, Mr and calculate relative molecular mass (and relative formula mass) as the sum of relative atomic masses
(h) perform calculations concerning reacting masses using simple proportions (calculations will not involve the mole concept)

- Syllabuses from SEAB

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2.6 Metallic Bonding

O Level - Pure Chemistry

(a) describe metals as a lattice of positive ions in a ‘sea of electrons’
(b) relate the electrical conductivity of metals to the mobility of the electrons in the structure

- Syllabus from SEAB

This section is covered only in the O Level (Pure Chemistry) syllabus.

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2.5 Covalent Bonding

O Level - Pure Chemistry

(a) describe the formation of a covalent bond by the sharing of a pair of electrons in order to gain the electronic configuration of a noble gas
(b) describe, using ‘dot-and-cross’ diagrams, the formation of covalent bonds between nonmetallic elements, e.g. H2; O2; H2O; CH4; CO2
(c) deduce the arrangement of electrons in other covalent molecules
(d) relate the physical properties (including electrical property) of covalent substances to their structure and bonding

O Level - Combined Chemistry

(a) describe the formation of a covalent bond by the sharing of a pair of electrons in order to gain the electronic configuration of a noble gas
(b) describe, using ‘dot and cross’ diagrams, the formation of covalent bonds between nonmetallic elements, e.g. H2, O2, H2O, CH4 and CO2
(c) deduce the arrangement of electrons in other covalent molecules
(d) relate the physical properties (including electrical property) of covalent substances to their structure and bonding

N(A) Level - Combined Chemistry

(a) describe the formation of a covalent bond by the sharing of a pair of electrons in order to gain the electronic configuration of a noble gas
(b) describe, using ‘dot and cross’ diagrams, the formation of covalent bonds between nonmetallic elements, e.g. H2; O2; H2O; CH4 and CO2
(c) deduce the arrangement of electrons in other covalent molecules
(d) relate the physical properties (including electrical property) of covalent substances to their structure and bonding

- Syllabuses from SEAB

Feel free to post questions related to this topic below. Do include your name and class (i.e. John, 4E3). Also, if you know the answers to questions that your friends posted, do respond to them!