3) Autocatalysis is a type of catalysis whereby one of the products of the reaction catalyses the reaction. (See lecture notes and page 119 TYS question 6)

• An example is the reaction between manganate(VII) and ethanedioate ions in acidic medium. Mn2+ formed acts as a catalyst for the reaction.
• The rate of such a reaction is slow at the beginning of the reaction (since there is hardly any catalyst).
• As the reaction proceeds, concentration of Mn2+ increases the rate of reaction increases.
• The rate of reaction will eventually decrease as concentration of reactants decreased to very low levels despite the increasing concentration of the catalyst.

4) When calculating rate constant, make sure u give the correct units based on the overall order of the reaction. Note that rate constant and rate is always positive or zero (never negative).

5) When drawing reaction pathway diagram (or commonly known as energy profile), make sure u label the two axes with the y-axis labelled "energy". There should be two horizontal lines, one labelled "reactants" and the other "products". Include the activation energy as well as the enthalpy change of reaction if the data are provided.

6) Activation energy is the minimum energy reactants must possess in order to overcome the energy barrier to form the products.

7) A catalyst increases the rate of a chemical reaction by providing an alternative reaction pathway with lower activation energy. This results in an increase in number of particles having energy greater or equal to activation energy, thus increasing the number of effective collision per unit time. Note that a presence of a catalyst will increase the rate constant but NOT the equilibrium constant.

8) The bond in O2 is a double bond, i.e. O=O. So make sure u quote the right bond energy when calculating the enthalpy change of atomisation for oxygen.

9) Bond breaking is endothermic and bond formation is exothermic.

10) For some definitions, if u r not sure of how to write in a statement, u should give the mathematical expression instead. For example, pH is the negative logarithm to base 10 of the concentration of H+ can be given as pH = -lg[H+].

11) In the electrolysis of brine, the purpose of the asbestos diaphragm is to prevent mixing of the products (Cl2 and NaOH). Thus, it prevents Cl2 from undergoing disproportionation in NaOH(aq) to form NaClO(aq) and NaCl(aq). Note that the diaphragm cell operates at relatively low temperature, NaClO3 is not formed.

12) Sodium hydroxide is used in making of soap (via saponification) and detergent, used in refining aluminium oxide and for manufacturing pulp, paper and textile (rayon - artificial silk). Note: the use of NaOH(aq) in school and college laboratory is NOT acceptable as a large scale use.

Chlorine gas is used as a germicide (sterilisation of water), bleaching agent (for cotton, linen & wood pulp), making polyvinylchloride (PVC used in water pipes). Note: the use of chlorine in manufacturing of CFCs is NOT acceptable.

Hydrogen gas is used in the making of ammonia (Haber Process), for the hydrogenation of fats and oil (manufacturing of margarine) and in metal welding using an oxy-hydrogen flame (2000 degree celsius).

13) For reaction of Cl2 with alkene, it is important to state the physical state of Cl2 (g, aq or in organic solvent such as CCl4) since different products will be obtained.

14) When describing colour change, there is a need to state the initial colour. E.g. Orange K2Cr2O7 turns green.

15) When analysing mass spectrum, make sure that the species are singly positively charged unless otherwise stated by the question.

16) Labile protons are found in alcohols, phenol, carboxylic acids, primary amines, secondary amines, primary amides and secondary amides.