### definitions

Posted:

**Thu Mar 07, 2019 11:06 pm**Can someone define zero, first, second order reactions? I thought it had to do with how many components are coming together, but that wouldn't make sense for a zero order rxn.

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=147&t=43811

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Posted: **Thu Mar 07, 2019 11:06 pm**

Can someone define zero, first, second order reactions? I thought it had to do with how many components are coming together, but that wouldn't make sense for a zero order rxn.

Posted: **Fri Mar 08, 2019 1:38 am**

It refers to the exponents on the concentrations. We designate these orders usually in terms of each reactant. So, in something like rate = k[A]^{0}, reaction rate is independent of concentration of A itself. Thus, it's zero order with respect to A. Same idea for other orders.

Posted: **Fri Mar 08, 2019 3:07 am**

I am also led to believe that these values have to be experimentally found, and are not just based off of something you can look at a chemical equation and tell. For example, if you have 1 mol of x that produces 1 mol of product then you have 2 mol of x that produces 2 mol of product you can see this increases by an exponent of 1 so it is of first-order. If you have 1 mol of y that produces 1 mol of product and then have 2 mol of y that produces 4 mol of product then you can see this increases by an exponent of 2 so it is of second-order. Lastly, if you have 1 mol of z that produces 1 mol of product and then you have 2 mol of z that produces 1 mol of product then you can see this increases by an exponent of 0 since it instead just relies on the rate constat thus it is of zero-order.