Summary of Sections

1 Information concerning the relative amounts of reactants and products taking part in a chemical reaction is known as the stoichiometry of the reaction. 

2 In general terms, a reaction mechanism provides a molecular description of how reactants are thought to be converted into products during a chemical reaction. 

3 An elementary reaction is one that takes place in a single step, does not involve the formation of any intermediate species, and which passes through a single transition state. 

4 A chemical reaction that proceeds by a series of elementary steps is known as a composite reaction and the corresponding mechanism is referred to as a composite reaction mechanism, or just composite mechanism. 

5 All reaction mechanisms with more than one step will involve intermediate species. These are formed in one step and consumed, in some way, in another. 

1 Molecular mechanics is based on a simplified model of bonding but can produce useful results for large molecules, such as proteins and solids. 

2 For ionic solids, the model is of ions held together mainly by electrostatic interaction with some contribution from intermolecular forces. 

3 Aluminosilicates such as zeolites are more sensitive to intermolecular forces between ions and in addition require a term that retains the ZOSiO and ZOAIO angles. 

4 Modelling of organic molecules uses partial charges rather than the formal charges of the ionic model. 

5 The most important terms for organic molecules are those that use spring-like functions to retain the bond lengths, bond angles and torsion angles. 

1 Oxidation states or oxidation numbers may be regarded as charges, usually fictitious, which are assigned to elements in compounds by assuming that shared electron pairs in covalent bonds are completely transferred to one of the two bound atoms. Transfer is assumed to occur to the more electronegative of the two. 

2 Oxidation is an increase in oxidation number reduction is a decrease. 

3 Redox reactions may be represented by balanced equations. Oxidation numbers are assigned to those substances involved in the oxidation/reduction. The total change in oxidation number is set to zero by adjusting the numbers of reactants and products. In aqueous solution, H2O, H+Caq) or OH (aq) ions are included as necessary to balance the number of hydrogen and oxygen atoms. 

The ten substances listed below contain sulfur. Work out the oxidation number of sulfur in each one. Then present your results in the form of a table, showing the substances in order of increasing sulfur oxidation number. 

By working out the relevant oxidation numbers, specify which of the following are redox reactions and state which element is oxidized, and which is reduced. 

1 Chemistry is a practical subject, requiring specialist apparatus to perform most chemical reactions. 

2 Chemists have a unique style of describing and writing-up experiments. 

3 A risk assessment must always be made before performing any experiment. 

4 It is sometimes necessary to perform reactions under a dry, inert gaseous atmosphere, to exclude all traces of moisture and oxygen. 

The following is taken from a student s badly written laboratory notebook. 

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Armstead, H. C. H. 1975a. Summary of Section VIII. Electricity production. In Proceedings Second United Nations Symposium on the Development... 

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