## Determining Reaction Order

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

AlyssaPeckham1A
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### Determining Reaction Order

could someone further explain how to determine reaction orders?

Akash_Kapoor_1L
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### Re: Determining Reaction Order

To determine reaction order you would add the coefficients of the concentrations in the Rate law. For example, if the rate law = k[A]^2 * [B]:
The Reaction is Second-Order in terms of A, First-Order in terms of B, and (2+1) Third-Order overall.

skalvakota2H
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Joined: Sat Jul 22, 2017 3:01 am

### Re: Determining Reaction Order

The reaction order is determined experimentally. Thus, the pattern is as follows:
If the reactant concentration is doubled and the rate is unchanged, then the reactant is zero order.
If the reactant concentration is doubled and the rate is doubled, then the reactant is first order.
If the reactant concentration is doubled and the rate is quadrupled, then the reactant is second order.

First find the individual order for each reactant and assign this number as the exponent in the rate law for the particular reactant. The overall order can be given by taking the sum of the exponents.

Angel R Morales Dis1G
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Joined: Sat Jul 22, 2017 3:01 am

### Re: Determining Reaction Order

You can also determine reaction order from the rate constant:
K=1/s first order
K=1/M*S second order
K=1/M^2*S third order
You get these units for k by doing this: K= M^(1-X)/S; where X is the order of the reaction. Just a helpful hint to find those units :)

kaushalrao2H
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### Re: Determining Reaction Order

in general, the only way to determine the reaction order is experimentally or via the reaction mechanism.

Pooja Nair 1C
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### Re: Determining Reaction Order

The reaction order is found experimentally, and is usually stated in the question itself. For zero order, rate = k; for first order, the rate is k*[A]; and for second order, the rate is k*[A]^2