Rate Laws - Oneonta

Section 14.5 Activation Energy and Temperature Bill Vining SUNY Oneonta Activation Energy and Temperature

In this section a. Reaction coordinate diagrams b. The Arrhenius equation c. Temperature, Ea and k d. Graphical determination of Ea Reaction Coordinate Diagrams

Numerical connection between Ea and EE Activation Energy, Temperature and Rate Activation Energy, Temperature and

Rate Trends: As Ea decreases, rate increases As T increases, rate increases Why do reactions go faster at higher temperature?

Why do reactions go faster with lower activation energy? The Arrhenius Equation Trends: k = rate constant

A = frequency factor Ea = activation energy R = gas constant (8.3145 J/K mol)mol) T = temperature (K) As T:

As Ea: The Arrhenius Equation: Two Point Version General Use: k1 = rate constant at temperature 1 k2 = rate constant at temperature 2

T1 = temperature 1 (K) T2 = temperature 2 (K) Ea = activation energy R = gas constant (8.3145 J/K mol)mol) There are five variables. If you know 4 of Them you can solve for the 5th.

The Arrhenius Equation: Two Point Version The activation energy for the gas phase decomposition of t-butyl propionate is 164 kJ. C2H5COOC(CH3)3(g) (CH3)2C=CH2(g) + C2H5COOH(g) The rate constant for this reaction is 3.80 10-4 s-1 at 528 K. What is the rate constant at 569 K?

The Arrhenius Equation: Two Point Version The rate of a reaction triples when the temperature is increased from 280 oC to 300 oC. What is the activation energy? The Arrhenius Equation: Graphical

Determination of Ea k = rate constant A = frequency factor Ea = activation energy R = gas constant (8.3145 J/K mol)mol) T = temperature (K)

1 ln ( )= ln ( ) y

= b + m x Collect k vs. temperature data Plot ln(k) vs. 1/T Ea = - slope x R

Graphical Determination of Elna ( )= ln ( ) 1