## Know Which Order It Is [ENDORSED]

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

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JaeHoCho1B
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Joined: Sat Jul 09, 2016 3:00 am

### Know Which Order It Is

Hello! I was wandering how can we tell what kind of order the reaction is based off the rate? Thank you so much for your help!

Chem_Mod
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### Re: Know Which Order It Is  [ENDORSED]

One way is based off how the rate varies with concentration. If the concentration increases two-fold and the rate increases two-fold, you know that the reaction is first order. Similarly, if the concentration increases two-fold and the rate increases by a factor of 4, then you know the reaction is second order.

Desiree Martin 2A
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Joined: Fri Jul 22, 2016 3:00 am

### Re: Know Which Order It Is

As well as this, another thing to consider is the overall order of the reaction. Depending on the amount of reactants, aA+bB=cC+dD, you must find the order of each reactant, then add the sum of the orders to get the OVERALL order. For example, let's say rate law =k[A]^2 * [B]^2, then the overall order is 2+2=4. From here, they would usually ask to find k. If given the table of values for different concentrations of A and B as well as the rate, then you would simply focus on one line, and plug in k=(rate of reaction)/[A]^2*[B]^2. Then once k is found, you have found the rate law for that reaction by plugging in the value of k to the original equation of the rate law.

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