key term - Turnover Number

Definition

Turnover number is a measure of the efficiency of a catalyst, defined as the number of substrate molecules converted to product per catalyst molecule per unit time, usually expressed in terms of seconds. This concept is crucial in understanding how effective a catalyst is in speeding up chemical reactions without being consumed in the process. A higher turnover number indicates a more effective catalyst, highlighting its importance in various catalytic applications, especially in homogeneous catalysis and industrial settings with organometallic catalysts.

5 Must Know Facts For Your Next Test

1. Turnover number is typically expressed in units of seconds, which reflects how quickly the catalyst can convert substrates to products.
2. In homogeneous catalysis, catalysts are present in the same phase as the reactants, which can lead to higher turnover numbers due to better interaction between the catalyst and substrate.
3. Turnover numbers can vary widely depending on the nature of the catalyst and the specific reaction conditions.
4. A high turnover number can indicate both high catalytic activity and stability, suggesting that the catalyst can be reused multiple times without significant loss of effectiveness.
5. Turnover frequency (TOF) is closely related to turnover number, as it refers to the number of turnovers per unit time, providing insights into the kinetics of catalytic reactions.

Review Questions

• How does turnover number impact the evaluation of catalyst performance in chemical reactions?
  • Turnover number is crucial for assessing catalyst performance because it quantifies how many substrate molecules are transformed into products by a single catalyst molecule over time. A high turnover number suggests that the catalyst is highly efficient and effective at promoting the reaction. Understanding this concept helps chemists compare different catalysts and optimize conditions for maximum efficiency.
• Discuss the significance of turnover number in industrial applications, particularly concerning organometallic catalysts.
  • In industrial applications, especially those utilizing organometallic catalysts, turnover number plays a vital role in determining cost-effectiveness and sustainability. A catalyst with a high turnover number allows for more product yield with less catalyst required, which can significantly lower production costs and reduce waste. This efficiency is essential for scaling up reactions to commercial levels while maintaining economic viability.
• Evaluate how variations in reaction conditions can influence turnover number and what this means for catalytic processes.
  • Variations in reaction conditions such as temperature, pressure, and solvent can significantly influence turnover number by affecting the stability and activity of the catalyst. For instance, increased temperature may enhance kinetic energy and improve reaction rates but could also lead to catalyst degradation. Understanding these influences enables chemists to tailor conditions that maximize turnover number while ensuring catalyst longevity, thereby optimizing overall catalytic efficiency and effectiveness in both research and industrial settings.

Related terms

Catalysis:

The process of increasing the rate of a chemical reaction by adding a substance (catalyst) that is not consumed in the reaction.

Catalyst: A substance that increases the rate of a chemical reaction without undergoing permanent chemical change.

Selectivity:

The ability of a catalyst to favor the formation of a specific product or products in a chemical reaction over others.