The Damköhler number compares the rate of reaction to the rate of convective transport. Which of the following statements is true?

• A. A high Da indicates the reaction rate dominates transport
• B. Da has no relation to transport
• C. Da only applies to gas-phase reactions
• D. Da is always less than 1 for all reactors

Answer: (A)

The key idea is that the Damköhler number compares how fast the chemistry would proceed to how fast reactants are brought to or moved through the reactive zone. It’s a ratio of the reaction rate to the transport rate, so it tells you which process is controlling the overall rate.

When this ratio is large, the reaction proceeds quickly compared with the pace of convective transport. In that regime, the observed behavior and extent of reaction are governed primarily by the kinetics—the chemistry dominates the comparison with transport. In other words, the reaction rate is the stronger factor relative to how fast material is being moved, so the statement about the reaction rate dominating the transport is the best description.

The other ideas don’t fit as well: Da is fundamentally about the relationship between reaction and transport, so it does relate to transport and isn’t restricted to gas-phase reactions only; its value can be greater than or less than 1 depending on conditions, so it isn’t universally less than 1.