## Determining Order

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

805312064
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### Determining Order

If we are not given a graph, how do you determine the order of a reaction? Do we have to write out all the reaction mechanism steps?

jisulee1C
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### Re: Determining Order

It depends on how the problem is given to you. If there is the chart, with different concentrations and rates you can determine the order with respect to a reactant. Or if the rate constant is given in units you can determine the overall reaction order.

Vincent Leong 2B
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### Re: Determining Order

The rate constant and elementary rxns can determine rate order.

Martina
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### Re: Determining Order

You can also look at units of the rate constant if it is given and be able to tell what the order is.

Maika Ngoie 1B
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### Re: Determining Order

Martina wrote:You can also look at units of the rate constant if it is given and be able to tell what the order is.

Yes! for zero order reactions the units are M/s. First order is s^-1, and second order is 1/M.s.

Julie_Reyes1B
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### Re: Determining Order

Maika Ngoie 1B wrote:
Martina wrote:You can also look at units of the rate constant if it is given and be able to tell what the order is.

Yes! for zero order reactions the units are M/s. First order is s^-1, and second order is 1/M.s.

The way that I remember this is that rate is in the units M/s, then when you solve for k you have to divide by the concentration of the reactant. 0 order is [A]^0 which is 1, so you do not divide by anything and K will still have the units of M/s. 1st order has [A]^1 with units of M, so when you divide the units cancel and you are left with 1/s. 2nd order has [A]^2 with units of M^2. so when you divide by M^2 the result is 1/mS

005384106
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### Re: Determining Order

Does the larger the order mean that the more collisions will occur?

Michelle Xie 2B
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### Re: Determining Order

You can look at units of rate constant for the orders of each reactant and add them together.