Selectivity

What is this formula?

Selectivity measures how preferentially a reaction forms the desired product relative to undesired byproducts.

When to use it

Use this formula when evaluating reaction performance, catalyst effectiveness, process optimization, and competing reaction pathways.

Example

Given:

Desired product formed = 4.5 mol

Byproducts formed = 0.5 mol

Formula:

S = ndesired / nbyproducts

Substitution:

S = 4.5 / 0.5

Result:

S = 9

The reaction produces nine moles of desired product for every mole of byproducts formed.

Applications

Organic synthesis

Catalysis

Petrochemical processing

Reaction engineering

Industrial chemistry

Note

Several definitions of selectivity exist in the chemical engineering and organic chemistry literature. This version expresses selectivity as the ratio of desired product formed to undesired byproducts formed and is one of the most common definitions for comparing reaction performance.

Some authors define selectivity relative to reactant consumption or as a percentage. When comparing values from different sources, the exact definition should always be verified.