1. Chemistry 1011 Slot 51 Chemistry 1011 TOPIC Rate of Reaction TEXT REFERENCE Masterton and Hurley Chapter 11

2. Chemistry 1011 Slot 52 11.6 Reaction Rate and Temperature YOU ARE EXPECTED TO BE ABLE TO: Use the kinetic theory of gases to explain the effect of temperature on reaction rate. Use the Arrhenius equation to determine the activation energy for a reaction given appropriate rate data.

3. Chemistry 1011 Slot 53 Reaction Rate and Temperature Most reaction rates increase with temperature A 10 o rise in temperature will double the rate of reaction Food cooks faster in a pressure cooker Food spoils faster outside a refrigerator

4. Chemistry 1011 Slot 54 Using the Kinetic Theory of Gases At any given temperature, only a fraction of molecules possess enough energy to react Raising the temperature raises the average energy of the molecules. This substantially increases the number of molecules possessing the energy necessary to react

5. Chemistry 1011 Slot 55 Temperature effect on energy

6. Chemistry 1011 Slot 56 The Arrhenius Equation Remember that k = p x Z x e -E a /RT –Assume that p is not temperature dependent –Z is only somewhat temperature dependent then k = Ae -E a /RT A is a constant (R is the gas constant) (T is the absolute temperature in Kelvin)

7. Chemistry 1011 Slot 57 The Arrhenius Equation k = Ae -E a /RT Taking logs: ln k = ln A  E a /RT This is the Arrhenius Equation It represents a straight line with slope  E a /R

8. Chemistry 1011 Slot 58 Arrhenius Equation Plot ln k = ln A  E a /RT Slope =  E a /R =  1.61 x 10 4 E a =  R x slope =  (8.31J/mol)(  1.61 x 10 4 K) E a = 134kJ/mol

9. Chemistry 1011 Slot 59 Calculating E a from two Data Points Given two rate measurements at two different temperatures: ln k 2 = ln A  E a /RT 2 ln k 1 = ln A  E a /RT 1 Subtract the second from the first ln k 2  ln k 1 =  E a /R[1/T 2  1/T 1 ] ln k 2 / k 1 = E a T 2  T 1 R T 2 T 1

10. Chemistry 1011 Slot 510 Example 11.6 Rate constant doubles when temperature increases from 15 o C to 25 o C –Calculate E a –Calculate k at 100 o C Use “two point” method to find E a Use ln k 2 / k 1 = E a T 2  T 1 R T 2 T 1 to find k 2