When to use each order

[205192823]

How do I know when it’s zero, first, and second order?

[VPatankar_2L]

You can tell the orders based on the graphs: for zero-order the graph of [A] vs time would be linear, for first-order the graph of lnA vs time would be linear, and for second-order the graph of 1/[A] vs time would be linear. You can also determine the order based on a data table by using experiment trials to determine the order for each reactant. You would look for the results in which the reactant whose order you are not calculating is being held constant while the reactant whose order you are trying to calculate is changing. You would compare the ratio of change in reactant concentration to the ratio of the rate to derive the order. Elementary steps of a reaction can also tell you the order of each reactant based on the coefficients.

[Adam Kramer 1A]

The order is the sum of the exponents in the rate law. You simply add them and whatever the sum is is the order of the reaction

[Felicia Wei 1B]

Order is determined experimentally first. You can only find K once you have determined the order. In the lecture today Professor Lavelle went over how to identify this graphically. You want to look for the graph that will give you a straight line and that slope is K. Do this by graphing [A] vs t, ln[A] vs t, and/or 1/[A] vs t. Whichever one gives a straight line will determine if it is zero order, first order, or second-order(respectively).

[Joseph_Armani_3K]

Algebraically, the order is the sum of the reactant concentrations' exponents. So if the rate = k[A][B], the reaction order would be 2 because 1+1=2

Graphically, the graph that is the most linear out of the three (A vs time, lnA vs time, 1/A vs time) is the reaction's order.

[Claudia_Danysh_2B]

Essentially graphing the information of [A] vs. time, ln[A] vs. time, or 1/[A] vs. time can tell you which order your reaction is in.

[Simi Kapila_3E]

If you look at the reaction graphically, if it is [A] vs time and is linear, then it is a 0 order reaction. If it is ln[A] vs time and is linear, then it is a first order reaction, if it is 1/[A] vs time and is linear, then it is a third order reaction

[Nayra Gharpetian 3F]

i think it's easiest to look at it graphically. if you graph ln [A] vs time and you get a straight line with a negative slope, this is first order. If you graph 1/[A] vs time and you get a straight line with positive slope, this is second order. if you graph [A] vs time and you get a straight line with a negative slope, this is zero order. these are the three orders that we will most commonly see.

[Brian Nguyen 2I]

You can determine order based on different graphs. [A] vs. Time is linear for zero order, ln[A] vs. Time is linear for first order, and 1/[A] vs. Time is linear for second order.

[Mina Tadros 3L]

When the plot of [A] vs. time is linear, then it is zero-order. When the plot of ln[A] vs. time is linear, then it is first-order. When the plot 1/[A] vs. time is linear, then it is second-order.

[FionaHunter21]

You would have to either use rate laws and divide them to find the order of each reactant or you would need to plot the equation using one of the integrated rate laws and see which one makes a linear plot.

[shevanti_kumar_1E]

There are multiple ways to identify which order to use.
1. Look at the graphs
2.Look at the units of the rate constant
3. Might be specified in the problem
4. Experimental data if its given in the problem

I've attached a really helpful graphic organizer.

[Tanner Bartyczak 1K]

Thanks for the graph. That is really helpful.

[Chelsea_Guzman_3C]

In order to determine which order, you can sum up the exponents in the rate law. However, i find the graphs to be more useful, so I really appreciate whoever posted that!

[Lilly Catarozoli 1B]

You can sum up the exponents from the rate law or look at the graphs!

[David Liu 1E]

like everyone else said, you look at the sum of the rate law exponents!

[jasmineculilap_3F]

You can add the exponents in the rate law together, use the units of the rate constant, or use graphs.

[Nan_Guan_1L]

Dr. Lavelle talked about many aspects that you can use to tell whether a reaction is zero, first, second order. for one you can look at the graphs if given; you can also look at the values of half lives; you can also do a ratio of two rates of the same reaction, and see what the exponential is, which denotes the order of the reaction.

[Joshua Swift]

You can determine orders either by the graphs, units, or by looking at the rates in relationship to changing concentrations.

[Michael Cardenas 3B]

Thank you for the graph it is really helpful!