1. Tímea Szentgyörgyi 1021 Hungary, Budapest, Hűvösvölgyi u. 131. Tel.:36-1-394-2968; Fax: 36-1-200-6615 www.sek.hu; www.sek.net SEK Budapest International School Rates of Reactions

2. Chemical kinetics is the study of the speed with which a chemical reaction occurs and the factors that affect this speed. Chemical kinetics is the study of the speed with which a chemical reaction occurs and the factors that affect this speed. The rate of a reaction is the speed at which a reaction happens. The rate of a reaction is the speed at which a reaction happens. All the molecular level of life some reactions go very rapidly and other take forever. All the molecular level of life some reactions go very rapidly and other take forever.

3. The rate of reaction, r, is defined to be the slope of the concentration-time plot for a species divided by the stoichiometric coefficient of that species. The rate of reaction, r, is defined to be the slope of the concentration-time plot for a species divided by the stoichiometric coefficient of that species.

4. A + 2 B = 3 C A + 2 B = 3 C r = -d[A]/dt = -1/2 d[B]/dt= 1/3 d[C]/dt r = -d[A]/dt = -1/2 d[B]/dt= 1/3 d[C]/dt The reactants have a negative slope, because they are being consumed in the reaction. Products have a positive slope, because they are being formed in the reaction. The reactants have a negative slope, because they are being consumed in the reaction. Products have a positive slope, because they are being formed in the reaction.

5. What factors affect the rate of a reaction? The concentration of the reactants. The more concentrated the faster the rate. Remember for gasses, increasing the pressure simply increases the concentration so that's the same thing. The concentration of the reactants. The more concentrated the faster the rate. Remember for gasses, increasing the pressure simply increases the concentration so that's the same thing.

6. What factors affect the rate of a reaction? Temperature. Usually reactions speed up with increasing temperature. Temperature. Usually reactions speed up with increasing temperature. Physical state of reactants. Powders react faster than blocks - greater surface area and since the reaction occurs at the surface we get a faster rate. Physical state of reactants. Powders react faster than blocks - greater surface area and since the reaction occurs at the surface we get a faster rate. The presence of a catalyst (or inhibitor). A catalyst speeds up a reaction, an inhibitor slows it down. The presence of a catalyst (or inhibitor). A catalyst speeds up a reaction, an inhibitor slows it down.

8. Reaction with High Rates: Reaction with High Rates: 1. FeCl 3 + KSCN → Fe( SCN) 3 + 3 KCl 1. FeCl 3 + KSCN → Fe( SCN) 3 + 3 KCl 2. Faro’s snake 2. Faro’s snake Reaction with Middle Rates: Reaction with Middle Rates: FeCl 3 + Na 2 S 2 O 3 → [ Fe( S 2 O 3 ) 2 ] - FeCl 3 + Na 2 S 2 O 3 → [ Fe( S 2 O 3 ) 2 ] - Halloween reaction / Old Nassau Reaction Halloween reaction / Old Nassau ReactionOld Nassau ReactionOld Nassau Reaction

9. The reaction in this The reaction in this experiment takes place in several steps [5]. several steps [5]. First, sodium First, sodiummetabisulphite reacts with water to form sodium hydrogen sulphite: Na 2 S 2 O 5 + H 2 O ==> 2NaHSO 3 2NaHSO 3 Hydrogen sulphite ions Hydrogen sulphite ions reduce iodate(V) ions to iodide ions: IO 3 - + 3 HSO 3 - ==> IO 3 - + 3 HSO 3 - ==> I - + 3 SO 4 2+ 3H +

10. Once the concentration of iodide ions is large enough that the solubility product of HgI 2 is exceeded, orange mercury(II) iodide solid is precipitated until all of the Hg 2+ ions are used up (provided that there is an excess of I - ions). Once the concentration of iodide ions is large enough that the solubility product of HgI 2 is exceeded, orange mercury(II) iodide solid is precipitated until all of the Hg 2+ ions are used up (provided that there is an excess of I - ions). Hg 2+ + 2 I - ==> HgI 2 (orange or yellow) Hg 2+ + 2 I - ==> HgI 2 (orange or yellow)

12. If there are still I- and IO3 - ions in the mixture, the iodide-iodate reaction If there are still I- and IO3 - ions in the mixture, the iodide-iodate reaction IO 3 - +5 I - + 6 H + ==> 3 I 2 + 3 H 2 O IO 3 - +5 I - + 6 H + ==> 3 I 2 + 3 H 2 O takes place and the blue starch-iodine complex is formed, takes place and the blue starch-iodine complex is formed, I 2 +starch ==>complex (blue or black) I 2 +starch ==>complex (blue or black)

13. Reactions with low rates: 1. Pb( CH 3 COO) 2 + 2KI = PbI 2 +CH 3 COOK 1. Pb( CH 3 COO) 2 + 2KI = PbI 2 +CH 3 COOK 2.NiCO 3 +2 dmg= [Ni( dmg) 2 ] 2+ + CO 3 2- 2.NiCO 3 +2 dmg= [Ni( dmg) 2 ] 2+ + CO 3 2- 3.CoSO 4 +2NH 4 SCN=Co(SCN) 2 + (NH 4 ) 2 SO 4 3.CoSO 4 +2NH 4 SCN=Co(SCN) 2 + (NH 4 ) 2 SO 4

14. Thank you for your attention