Yield and Selectivity

  • Yield: The actual amount of products formed relative to what is actually expected from the reaction. \[\text{% Yield} = \frac{\text{actual amount of product formed}} {\text{theoretical amount of product expected}} \times 100\]

  • Selectivity: The ratio of the moles of the desired product produced to the moles of undesired product (by-product). \[\text{Selectivity} = \frac{\text{moles of desired product formed}}{\text{moles of undesired product formed}}\]

For example, methanol (\(\ce{CH3OH}\)) can be converted into ethylene (\(\ce{C2H4}\)) and propylene (\(\ce{C3H6}\)) by the reactions: \[\begin{aligned} \ce{2CH3OH} &\rightarrow \ce{C2H4} + \ce{2H2O} \\ \ce{3CH3OH} &\rightarrow \ce{C3H6} + \ce{3H2O}\end{aligned}\] If the desired product is ethylene, then the selectivity is computed as: \[\text{Selectivity} = \frac{\text{moles of ethylene formed}}{\text{moles of propylene formed}}\]