(a) (i) State the collision theory of reaction rates.
(ii) Using the collision theory, explain briefly how temperature can affect the rate of a chemical reaction.
(b) (i) Sketch a graphical representation of Charles’ law.
(ii) Calculate the volume of oxygen that would be required for the complete combustion of 2.5 moles of ethanol at s.t.p.
[molar volume at s.t.p = 22.4 dm(^3)]
(c) (i) Define esterification.
(ii) Give two uses of alkanoates.
(iii) Give the products of the alkaline hydrolysis of ethyl ethanoate.
(d) A tin coated plate and a galvanized plate were exposed for the same length of time.
(i) Which of the two plates corrodes faster?
(ii) Explain briefly your answer in 2 (d) (i).
Explanation
(a)(i) States that atoms, molecules/ions / particles / reactants involved in a chemical
reaction must collide before reaction can take place.
(ii) When temperature is increased/decreased the reacting molecules gain / lose kinetic energy and move faster / slower.
Frequency of collision and effective collision increases/decreases therefore rate of reaction increases/decreases.
(The explanation must correspond to score)
(ii) C(_6)H(_5)OH(_{(aq)}) + 3O(_{2(g)}) → 3H(_2)O(_{(l)}) + 2CO(_{2(g)})
From the equation 1 mole of ethanol requires 3 x 22.4 dm(^3) of oxygen
2.5 mols = (frac{2.5 times 3 times 22.4}{1})
= 168.0 dm(^3)
(c) (i) Esterification is the reaction between an alkanol and alkanoic acid to produce an alkanoate / ester (and water in the presence of a mineral acid.)
(ii) – used as solvents (e.g. for paints, nail, varnishes, lacquer, adhesives and
cellulose nitrates)
– used in perfumes/cosmetics
– used in (artificial) flavouring for foods
– production of soap
– plasticizers
(iii) ethanol / C(_2)H(_5)OHand sodium ethanoate (CH(_3)COONa) / potassium ethanoate(CH(_3)COOK)
(d)(i) Tin – coated plate
(ii) Zinc is more reactive than tin / higher in the electrochemical series than tin. When the tin coated plate is exposed, the plate goes into solution / corrodes. In zinc coated (galvanized) plate, it is the zinc that dissolves / corrodes hence protecting the plate better and zinc coated plate does not corrode.