2.5 – Fractional Conversion Yield Selectivity Excess

2.5.0 – Learning Objectives

By the end of this section you should be able to:

Understand the concepts of fractional conversion, yield, selectivity, and percent excess.

2.5.1 – Introduction

Fractional conversion, yield, selectivity, and percent excess are all important methods of describing how a chemical reaction progresses. They are useful values to solve material balances.

2.5.2 – Fractional Conversion

Fractional conversion is defined as the number of moles of a compound that reacted divided by the amount of the moles that were fed.

$Fractional<text>{}conversion={\frac {{\dot {n}}_{consumed}}{{\dot {n}}_{input}}}$

Another useful form of writing fractional conversion is

$Fractional<text>{}conversion={\frac {{\dot {n}}_{input}-{\dot {n}}_{output}}{{\dot {n}}_{input}}}$

2.5.3 – Yield (Fractional Yield)

Yield is defined as the moles of product formed divided by the ideal number of moles formed.

 $Yield={\frac {{\dot {n}}_{formed}}{{\dot {n}}_{ideal}}}$

The ideal number of moles formed is assuming that the limiting reactant reacts fully and that there are no side reactions.

2.5.4 – Selectivity

Selectivity is defined as the moles of desired products formed divided by the moles of undesired products formed.

 $Selectivity={\frac {{\dot {n}}_{product<text>{}desired}}{{\dot {n}}_{product<text>{}undesired}}}$

== 2.5.5 – Percent Excess

Percent excess is defined as the number of moles that are unreacted divided by the moles fed. $Percent<text>{}excess={\frac {{\dot {n}}_{input}-{\dot {n}}_{consumed<text>{}theoretically}}{{\dot {n}}_{consumed<text>{}theoretically}}}$

Note: any of these terms above can be expressed as a percent (by multiplying 100 to the values)