## Identifying Zero vs. First vs. Second Order Reactions

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

EllieSchmidtke_4I
Posts: 51
Joined: Wed Feb 20, 2019 12:16 am

### Identifying Zero vs. First vs. Second Order Reactions

How can you identify zero, first, and second order reactions?

Ryan 1K
Posts: 101
Joined: Fri Aug 09, 2019 12:15 am

### Re: Identifying Zero vs. First vs. Second Order Reactions

If given their graphs, you can see which graph provides a straight line based on the axes (ln [A] vs $\frac{1}{[A]}$ vs [A]). If given their rate laws or chemical equations, you can see how many molecules are involved in each reaction (molecularity).

chari_maya 3B
Posts: 108
Joined: Sat Sep 07, 2019 12:18 am

### Re: Identifying Zero vs. First vs. Second Order Reactions

In zeroth order, rate is independent of concentration of reactant so long as it is present in some quantity, in first rate is linearly dependent etc.

Chris Charton 1B
Posts: 69
Joined: Mon Jun 17, 2019 7:23 am

### Re: Identifying Zero vs. First vs. Second Order Reactions

You can do so by looking at the graphs produced by modeling the system as 0th, 1st or 2nd order. Which ever order produces a straight line is the correct order.

Kayli Choy 2F
Posts: 100
Joined: Sat Aug 24, 2019 12:17 am

### Re: Identifying Zero vs. First vs. Second Order Reactions

If you are given rate constants, you can also figure out whether a reaction is zero, first, or second order:
zero order: k = M/time
first order: 1/time
second order: 1/ (M * time)

Leonardo Le Merle 1D
Posts: 56
Joined: Wed Feb 27, 2019 12:16 am

### Re: Identifying Zero vs. First vs. Second Order Reactions

Also, if you are given various rates provided reactant concentrations, and rate does not change as a reactant concentration is increased or decreased, you know it is zeroth order. If it changes proportionately, it is first. If it changes exponentially, it is second or third or above.

Tanmay Singhal 1H
Posts: 143
Joined: Sat Jul 20, 2019 12:16 am

### Re: Identifying Zero vs. First vs. Second Order Reactions

once you start becoming more comfortable with the problems you will notice trends that allow you to determine the reaction order

Myka G 1l
Posts: 100
Joined: Fri Aug 30, 2019 12:17 am

### Re: Identifying Zero vs. First vs. Second Order Reactions

In a first order reaction, the rate of reaction is directly proportional to the concentration of a single reacting substance. Whereas in a 2nd order reaction the rate depends on the concentration of 2 reacting first order substances or a single reactant with a squared concentration. Because it depends on a single substance, the graph of a first order reaction is a straight line. For a zeroth order reaction the rate is solely dependent on the rate constant.