Zero order

[John Calonia 1D]

How can a reaction be completely independent of the concentrations of reactants?

[Akash J 1J]

I found this explanation on this website, I thought it did a good job of explaining some examples of why a reactant can be in zero order: https://chem.libretexts.org/Bookshelves ... _Chemistry)/Kinetics/02%3A_Reaction_Rates/2.10%3A_Zero-Order_Reactions

There are two general conditions that can give rise to zero-order rates:
1. Only a small fraction of the reactant molecules are in a location or state in which they are able to react, and this fraction is continually replenished from the larger pool.
2. When two or more reactants are involved, the concentrations of some are much greater than those of others

[IanWheeler3F]

Going off what Akash said, there's another example of adding a metal catalyst, and adding it makes it so much more likely that a reaction happens that it can change the order of a reactant to be zero since changing reactant concentration will have no effect on how fast the reaction is happening since its already happening at a maximum due to the catalyst. Increasing pressure in gaseous reactions can do the same since the reactants collide much more often.

[MariaCassol1L]

Another example is an enzyme catalyst in a biological reaction. So basically if you need the enzyme to make the reaction happen, the rate of the reaction will only depend on how long the enzyme takes to make the reaction happen if you have fewer enzymes compared to reactants (so the enzyme is never "free" it is always working and therefore saturated). So if you increase the reactant concentration it will not make a difference.

[Eve Gross-Sable 1B]

^ like the post above mentions, this is applied a lot to enzymes! In the microbio course I'm in right now we're studying enzyme kinetics and zero order reactions occur when the rate is directly proportional to the concentration of the substrate, while the rate therefore has nothing to do with the actual concentration of the substrate itself because it is always proportional.

[Tanner Bartyczak 1K]

I was also wondering this. Thanks for the explanation.

[Nicoli Peiris 1B]

This can happen when an enzyme or catalyst is working as hard as it can and any increase in concentration does not increase the rate of the reaction. Similarly, if a reactant is not in the rate limiting step/mechanism, its concentration does not affect the over all rate.

[Neha Jonnalagadda 2D]

Also if there is a catalyst, there is a chance that the order of the reaction will be zero!

[Emily Quill 2H]

Hi! One explanation is that the concentrations of some reactants are a great deal larger than the others' concentrations.