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.

\[Fractional \space conversion = \frac{\dot{n}_{consumed}}{\dot{n}_{input}}\]

Another useful form of writing fractional conversion is

\[Fractional \space conversion = \frac{\dot{n}_{input}-\dot{n}_{output}}{\dot{n}_{input}}\]

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.

\[Selectivity= \frac{\dot{n}_{product\space desired}}{\dot{n}_{product\space undesired}}\]

2.5.5 – Percent Excess¶

Percent excess is defined as the number of moles that are unreacted divided by the moles fed.

\[Percent \space excess = \frac{\dot{n}_{input}-\dot{n}_{consumed\space theoretically}}{\dot{n}_{consumed\space theoretically}}\]

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

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