4.2.5

Thermodynamics & Kinetic Control

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Thermodynamic & Kinetic Control

Reactions proceed due to a combination of favorable kinetics and thermodynamics. If one of these factors hinders the progression of a reaction, it is said to be controlling.

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Thermodynamic control

  • If there is enough energy in the system for the activation energy to be reached but the reaction does not proceed, then it is said to be under thermodynamic control.
  • This means that it is not thermodynamically favorable for the reaction to proceed.
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Examples of thermodynamic control

  • A simple example is trying to use a stone as fuel for a fire. The fire provides more than enough energy for activation but it is not thermodynamically favorable for the stone to react with oxygen.
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Kinetic control

  • Kinetic control occurs when a reaction does not occur at a measurable rate despite being thermodynamically favorable.
  • This is not because the position of equilibrium is to the left because the thermodynamics would favor a position to the right.
  • The reason is that there is not sufficient energy to overcome the activation energy.
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Examples of kinetic control

  • Fossil fuels react with oxygen when they burn. These reactions are very thermodynamically favored, both enthalpically and entropically.
  • So why does coal or oil or natural gas not spontaneously combust?
    • There is not sufficient energy to start the reaction.
    • In most cases, some sort of spark or fire is required to provide the activation energy.

Jump to other topics

1Structure - Models of the Particulate of Matter

2Structure - Models of Bonding & Structure

3Structure - Classification of Matter

3.1The Periodic Table: Classification of Elements

3.2Periodic Trends

3.3Group 1 Alkali Metals

3.4Halogens

3.5Noble gases, group 18

3.6Functional Groups: Classification of Organic

3.7Functional Group Chemistry

3.8Alkanes

3.9Alcohols

3.10Halogenoalkanes

4Reactivity - What Drives Chemical Reaction?

5Reactivity - How Much, How Fast & How Far?

6Reactivity - The Mechanisms of Chemical Change

7Measurement, Data Processing & Analysis

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