### 7.5.1. Third Body Terms

In cases that a third body is needed for the reaction to occur, the rate of progress described earlier is scaled by:

| (7–14)

where is the relative participation of component I i in reaction k.

For those components that have a high probability to participate in the reaction, the coefficient is higher than those that rarely participate or do not participate at all (). If the third body term is present in a reaction, CFX assumes the default efficiency for all components (Option = `Default`). Efficiency factors can be specified for individual species by setting Option to `Efficiency Factor List` and listing the components as well as their efficiency factors in the `Materials List` and `Efficiency Factor List` parameters, respectively. If the `Efficiency Factor List` option is effective, the default still applies to those components that are not listed.

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