## Zero Order Classification [ENDORSED]

$\frac{d[R]}{dt}=-k; [R]=-kt + [R]_{0}; t_{\frac{1}{2}}=\frac{[R]_{0}}{2k}$

Jake_Susi_2J
Posts: 13
Joined: Sat Jul 09, 2016 3:00 am

### Zero Order Classification

Hey I understand the rate law for a zero order reaction is rate=k but I am still confused on how we know what reactants are zero order, can someone help me clarify how one would go about this?

Aneesh_Gowri 1H
Posts: 21
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Zero Order Classification

So zero-order reactions occur when the rate is unaffected by the concentration of the reactants. So when there is an extremely little amount of a reactant, a zero-order reaction can occur, though it basically never happens in anything but a laboratory setting.
Hope this helps!

AnkitaNair1E
Posts: 17
Joined: Wed Sep 21, 2016 2:55 pm
Been upvoted: 1 time

### Re: Zero Order Classification  [ENDORSED]

Hi Jake,

So I think another way to understand what a zero order reaction means is to consider that you may have a reaction where the rate of the reaction doesn't depend on how much reactant you have. In other words, it could depend on another variable like enzymes or catalysts. For example, in our body, we have a lot of reactions that require catalysts or enzymes for the reaction to occur. In some cases, we have a limited amount of enzyme so no matter how much reactant we put in, the rate of the reaction stays the same because the enzyme is saturated and we need enzymes in order to form products.

To help explain this, consider the enzyme amylase which is responsible for helping us convert carbohydrates (from foods like bread) into glucose during digestion. Lets say you decide to eat an entire loaf of bread and you end up ingesting a lot of carbs. You could have a situation where the rate of your body digesting those carbs stays the same (even though you ate a lot more bread) because you only have enough amylase to digest half a loaf of bread at the time. In this scenario, the amylase in your body would be saturated, and you can't do anything to change your rate of digestion. Even eating more carbs doesn't help simply because you don't have enough amylase to digest it. As a result, we could say that the rate of the reaction (your digestion) doesn't depend on the concentration of reactant (the bread you eat) but only on a constant k (which we could define in this situation as the amount of amylase we have). This is essentially what a zero order reaction is.

So perhaps you're now wondering how to read the graph.[img]201495-163135946-9142-Capture.PNG[/img] Well essentially what this zero order reaction graph tells us is that slope or rate of the reaction of the experiment depends only on k (which we established before. Not the concentration of reactant). It also tells us that the concentration of reactant does get smaller over time (which makes sense when you think about the example in terms of digestion. Even though amylase could be saturated, it will eventually convert all the carbs into glucose) It also says that the reaction will be linear which means that it will happen at a constant rate unlike first and second order reaction where the rate is changing every second.

Hope this helped!
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