H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 1 Chapter 15 The Effect of Temperature Change and Catalyst on Reaction Rate 15.1Effect of Temperature Change on Reaction Rate in Terms of Activation Energy Rate in Terms of Activation Energy 15.2The Interpretation of Rates of Gaseous Reactions at Molecular Level Reactions at Molecular Level 15.3Energy Profile 15.4Catalysts and Their Effect on Reaction Rates

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Effect of Temperature Change on Reaction Rate in Terms of Activation Energy (SB p.50) Activation Energy Exothermic reaction Activation energy = energy required to break bonds (related to the rate of reaction)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Effect of Temperature Change on Reaction Rate in Terms of Activation Energy (SB p.50) Activation Energy Endothermic reaction Activation energy = energy required to break bonds (related to the rate of reaction)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Effect of Temperature Change on Reaction Rate in Terms of Activation Energy (SB p.51) Arrhenius Equation Where k is the reate constant of the reaction, A is a constant which is independent of temperature, e is the base of the natural logarithm, E a is the activation energy of the reaction in J mol -1, R is the ideal gas constant (i.e J K -1 mol -1 ). and T is the temperature in Kelvin. K = Ae –

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Effect of Temperature Change on Reaction Rate in Terms of Activation Energy (SB p.52) Determination of Activation Energy Using Arrhenius Equation In k = In A –

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Effect of Temperature Change on Reaction Rate in Terms of Activation Energy (SB p.52) Determination of Activation Energy Using two rate constants In k 1 = In A – ………………….(1) In k 2 = In A – ………………….(2) By substracting equation (2) from equation (1), we obtain: In k 1 /k 2 = ( 1/T 1 – 1/T 2 )

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 7 gas    Consider a sample of gas: Do all gas molecules move at the same speed? Why is there a distribution of molecular speeds even at a fixed temperature? 15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.55) Distribution of Molecular Speeds in a Gas Area under curve = total no. of gas molecules

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 8 Remarks With an increase in the temperature, the most probable speed increases. Actually the square of the average speed (c 2 )  absolute temp 15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.55) Change in the most probable speed

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 9 Remarks The distribution curve becomes flattened as the temp rises  fewer molecules will possess the most probable speed but there the proportion of fast moving molecules  15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.55) Increased proportion of fast-moving molecules

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 10 Effective collisions = collisions between reactant particles with high enough energies & proper orientations. In terms of Activation Energy: 15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.57) Simple Collision Theory

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 11 In terms of Collision Orientation: A Proper Orientation 15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.57) Simple Collision Theory HCl(g) + NH 3 (g) NH 4 Cl(s)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 12 Some Improper Orientations 15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.57)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Energy Profile (SB p.59) Energy Profile / activated complex

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 14 Rate = k[AB][C] Remark Thus the order of reaction is related to the mechanism 15.3 Energy Profile (SB p.59) Single-stage Reaction A-B + C  [A…B…C]  A + B +C

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 15 Example Rate = k[CH 3 CH 2 CH 2 CH 2 Br][H 2 O] Thus the orders of reaction are both 1 w.r.t.CH 3 CH 2 CH 2 CH 2 Br & H 2 O CH 3 CH 2 CH 2 CH 2 Br + H 2 O  CH 3 CH 2 CH 2 CH 2 OH + H + + Br Energy Profile (SB p.60)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 16 The slowest stage (stage 1) is the rate determining step (RDS) The order of r’x is 1 w.r.t. DE molecularity = 1 molecularity = 2 The order of r’x ~ the molecularity of the RDS 15.3 Energy Profile (SB p.61) Multi-stage Reaction Stage 1: D-E intermediate Stage 2: Intermediate + F D-F + E Overall reaction: D-E + F D-F + E Rate = k[DE]

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 17 Example Rate = k[(CH 3 ) 3 Br] (CH 3 ) 3 Br + H 2 O  (CH 3 ) 3 OH + H + + Br - i.e. 1st order w.r.t. (CH 3 ) 3 Br but 0th order w.r.t. H 2 O 15.3 Energy Profile (SB p.62)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 18 A + B  AB catalyst Mechanism 15.4 Catalysts and Their Effect on Reaction Rates (SB p.64) Catalysts and Reaction Rates Stage 1: A + catalyst A-catalyst Stage 2: A-catalyst + B A-B + catalyst Overall reaction: A + B A-B

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Catalysts and Their Effect on Reaction Rates (SB p.64) Energy profiles of the uncatalysed and catalysed pathways of a reaction

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Catalysts and Their Effect on Reaction Rates (SB p.64) Effect of catalyst on the fraction of particles

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 21 Catalyst Homogenous Catalyst Heterogenous Catalyst (Reactants & catalyst are in the same phase) (Reactants & catalyst are NOT in the same phase) A phase is a part of a system in which there is a uniform distribution of particles Catalysts and Their Effect on Reaction Rates (SB p.66)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Catalysts and Their Effect on Reaction Rates (SB p.65) Homogeneous Catalysis – Intermediate Formation A reactive intermediate is formed.

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Catalysts and Their Effect on Reaction Rates (SB p.65) reactive intermediate Energy Profile of Esterification

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 24 in different phase surface of MnO 2 for adsorption of H 2 O 2 H  O  O  H 15.4 Catalysts and Their Effect on Reaction Rates (SB p.67) Heterogeneous Catalysis – Adsorption 2H 2 O 2 (aq) MnO 2 (s) as catalyst 2H 2 O(l) + O 2 (g)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 25 in different phase surface of MnO 2 for adsorption of H 2 O 2 H  O  O  H 15.4 Catalysts and Their Effect on Reaction Rates (SB p.67) 2H 2 O 2 (aq) MnO 2 (s) as catalyst 2H 2 O(l) + O 2 (g) Heterogeneous Catalysis – Adsorption

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 26 in different phase surface of MnO 2 for adsorption of H 2 O 2 H  O  O  H 15.4 Catalysts and Their Effect on Reaction Rates (SB p.67) Heterogeneous Catalysis – Adsorption 2H 2 O 2 (aq) MnO 2 (s) as catalyst 2H 2 O(l) + O 2 (g)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 27 in different phase surface of MnO 2 for adsorption of H 2 O 2 H  O  O  H Partial bond formation Original bonds weaken Heterogeneous Catalysis – Adsorption 2H 2 O 2 (aq) MnO 2 (s) as catalyst 2H 2 O(l) + O 2 (g) 15.4 Catalysts and Their Effect on Reaction Rates (SB p.67)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 28 Applications of Catalysts Industrial Catalysts 15.4 Catalysts and Their Effect on Reaction Rates (SB p.68) 1.Iron is used in the Haber process. N 2 (g) + 3H 2 (g) Fe 2NH 3 (g) 2. Platinum or vanadium(V) oxide is used in the Contact process 2SO 2 (g) + O 2 (g) Pt or V 2 O 5 2SO 3 (g)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 29 Industrial Catalysts (triesters) Applications of Catalysts 15.4 Catalysts and Their Effect on Reaction Rates (SB p.69) 3. Nickel, platinium or palladium is used in the hydrogenation of unsaturated oils to make margarine. liquid solid

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 30 Industrial Catalysts 15.4 Catalysts and Their Effect on Reaction Rates (SB p.69) Applications of Catalysts 4. Nickel and nickel(II) oxide are used in the production of town gas in Hong Kong. C 5 H 12 (g) + 5H 2 O(g) Ni or NiO 5CO(g) + 11 H 2 (g) 2CO(g) + 2H 2 (g) CO 2 (g) + CH 4 (g)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 31 Applications of Catalysts Catalytic Converters in Car Exhaust Systems 15.4 Catalysts and Their Effect on Reaction Rates (SB p.69) 2CO(g) + 2NO(g) Rh 2CO 2 (g) + N 2 (g) C x H y (g) + ( x + y/4) O 2 (g) Pt xCO 2 (g) + y/2 H 2 O(g) 2CO(g) + O 2 (g) Pt 2CO 2 (g)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 32 Applications of Catalysts Enzymes in Biological Catalysts 15.4 Catalysts and Their Effect on Reaction Rates (SB p.69) C 6 H 12 O 6 (aq) yeast 2C 2 H 5 OH(aq) + 2CO 2 (g)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 33 The END