## General “order” question

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

Celeste 1I
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### General “order” question

What does “first” “second” or “zero” order even mean? And how can you tell the difference?

Tarika Gujral 1K
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Joined: Fri Sep 28, 2018 12:27 am

### Re: General “order” question

Order is essential to calculate kr, half life, change in concentration, or time needed to get to a particular concentration. There are different equations for each order. You’ll either be given order of reaction, or if you are given elementary reactions (and need to determine order of overall reaction), you can use molecularity of elementary reactions to determine overall order. Molecularity depends on reactants present.

Tatum Keichline 2B
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### Re: General “order” question

Zero order is time vs concentration
First order is time vs ln concentration
Second order is time vs 1/concentration

chloewinnett1L
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Joined: Fri Sep 28, 2018 12:20 am

### Re: General “order” question

The order refers to the exponent of concentrations of different species that must interact in order to form a product. For example, a zero order reaction, such as the evaporation of water or the decomposition of a single solid, does not depend on concentration and thus has an exponent of zero. If a reaction involves one aqueous species breaking down into two different aqueous species, or a gas decomposing into two different gases, that is first order because the rate of the reaction only depends on the concentration of one thing. Furthermore, a reaction involving two DIFFERENT species, such as NH4+(aq)+NO2-(aq)->N2(g)+2H2O(l), is second order because the rate depends on two different concentrations interacting. Hope that makes sense.

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### Re: General “order” question

Another Quick Question: how do we determine the first order reaction/how is it correlated with y=mx+C

Danny Elias Dis 1E
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### Re: General “order” question

MadelineHlobik wrote:Another Quick Question: how do we determine the first order reaction/how is it correlated with y=mx+C

For a first order reaction, you must look at the graph of ln[A] = -kt + ln[A]o. If this graph is a straight line with slope -k and y intercept ln[A]o, then you have a first order reaction. Typically you'll be given a graph or a data set and you'll need to apply this equation to it in order to decide if it is first order.

Brian Chang 2H
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Joined: Fri Sep 28, 2018 12:17 am

### Re: General “order” question

0th order reactions are time vs concentration.
1st order reactions are time vs ln(concentration).
2nd order reactions are time vs 1/concentration.