Ch_322a_10.07

Ch_322a_10.07 - Rates of Reaction: The Activation Energy...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Rates of Reaction: The Activation Energy The Standard Enthalpy Change, ! H o , is a thermodynamic parameter. It does not directly measure the rate of a reaction. The Activation Energy, E a Within Arrhenius reaction rate theory, the activation energy, E a , measures the rate of a chemical reaction. It is very similar to the enthalpy of activation, ! H , in Transition State Theory.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Analysis of the Chlorination of Methane The standard enthapy change, ! H o , and the activation energy, E a , are shown below for the initiation and propagation steps: intiation Cl 2 2Cl ! H o E a (kcal/mol) +58 +58 . propagation (1) Cl . + CH 4 HCl + CH 3 +1 +3.8 (2) . CH 3 . + Cl 2 CH 3 Cl + Cl . -25.5 ~+2 Although there is no way to directly calculate the E a from the ! H o , it may be experimentally measured.
Background image of page 2
Some General Correlations between ! H o and E a C Cl H H H Cl (DH o = -58) (DH o = -83.5) H 3 C-Cl + Cl . (1) Any reaction where bonds are broken will have an E a greater than zero, even if the ! H o is highly negative . The reason is that bond breaking runs ahead of bond making so the energy released in bond making is not completely available in the bond breaking step.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 10

Ch_322a_10.07 - Rates of Reaction: The Activation Energy...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online