Glossary term
Reaction Rate
Rate at which reactants are consumed or products are formed in a chemical, biochemical, or process reaction.
Definition
quantityReaction rate is the rate at which a chemical species is consumed or produced by reaction.
Reaction rate connects chemistry with reactor volume, conversion, selectivity, residence time, heat generation, scale-up, and process safety. It depends on concentration, temperature, catalyst state, mixing, phase contact, mass transfer, inhibition, side reactions, and operating history.
Reaction rate describes how fast reactants are consumed or products are formed. In a reactor balance, it converts chemistry into an engineering source or sink term. For species i, a rate of formation r_i may be positive for products and negative for consumed reactants, depending on the sign convention.
For a well-mixed reactor volume V:
where R_i is the net generation rate of species i. The rate expression may depend on concentration, temperature, catalyst activity, phase contact, pressure, inhibition, mixing, or mass transfer.
Engineering use
Reaction rate is used to estimate reactor size, conversion, yield, selectivity, residence time, heat generation, runaway risk, catalyst replacement, scale-up, and process control. A rate measured in a laboratory may not transfer directly to plant equipment if mixing, heat transfer, phase contact, or impurities change.
In exothermic systems, reaction rate and heat duty are coupled. A higher temperature can increase rate, which generates more heat, which can increase temperature further if cooling is inadequate.
Common mistakes
A common mistake is treating reaction rate as a fixed property of a chemical reaction. It is a function of conditions and may change with scale, catalyst age, mixing, impurities, mass transfer, and operating history. A strong reaction-rate review states basis, units, sign convention, temperature range, composition range, catalyst state, transport limits, uncertainty, and validation data.