Order of a reaction

[Pratika Nagpal]

How are we supposed to determine the order of a reaction.

In the textbook, it has been stated that decomposition of N205 has a=1 and N02 has a=2. How is this obtained.

I remember seeing somewhere that an order of a reaction if influenced by the order of the reactants and products. if this is true, how are the orders of the compounds in the reaction obtained ?

[Vince Li 2A]

The order for each reactant/product is typically obtained through experiments. Looking at a table which contains the initial concentrations of the reactants/products, and the initial rates, you are able to determine the order of the reactants/products. Remember the general rate law equation, which is rate = rate constant * concentration A^n * concentration B^m * concentration C*l. To find the order for reactant/product A, you would keep the other concentrations constant, and only change the concentration of A. Looking at the table, if doubling the concentration of A doubles the rate of the reaction, then A is first order (n = 1). If doubling the concentration of A quadruples the rate of the reaction, then A is second order. If doubling the concentration of A doesn't affect the rate at all, then it is zero order. Repeat this process for B and C to find the individual orders of reactants/products. To find the order of the reaction, you just add the individual orders together.

[George Hernandez 3I]

Like the previous reply mentioned, its based on experiments. If you refer back to Lavelle's monday week 9 lecture, he shows how experimentation determines the order of the reaction.

[Mari Williams 1K]

Will the experiments and results be likely given to us in a problem to interpret?

[EmilyGillen_1A]

Will the experiments and results be likely given to us in a problem to interpret?

Yes! I can't imagine that on an exam we would be given a problem where the necessary information wasn't already given to us. Doc. Lavelle mentioned it's really hard to find these values without an experiment, so on a test I feel that we would have to at least be given the results of an experiment that was done, and then the question might ask us to interpret. I would also be familiar with the graphs of each of the orders because we could also be given a problem where we have to translate the results of an experiment onto a graph.

[Pratika Nagpal]

The order for each reactant/product is typically obtained through experiments. Looking at a table which contains the initial concentrations of the reactants/products, and the initial rates, you are able to determine the order of the reactants/products. Remember the general rate law equation, which is rate = rate constant * concentration A^n * concentration B^m * concentration C*l. To find the order for reactant/product A, you would keep the other concentrations constant, and only change the concentration of A. Looking at the table, if doubling the concentration of A doubles the rate of the reaction, then A is first order (n = 1). If doubling the concentration of A quadruples the rate of the reaction, then A is second order. If doubling the concentration of A doesn't affect the rate at all, then it is zero order. Repeat this process for B and C to find the individual orders of reactants/products. To find the order of the reaction, you just add the individual orders together.

your response was very helpful. thank you .

[Gian Boco 2G]

Based on experiments and previous data

[Hasan Mirza 3F]

They will likely give a chart with experimental data which you can use to determine the order.

[gabbi_r2C]

If you're given the order of the reactants, then the overall order of the reaction is the sum of those reactants' orders. ie, if [NO] is 2 and [H2] is 1, then the overall order is 3.

[Brian Acevedo 2E]

The order of an overall reaction is equal to the sum of the orders of the individual reactants. If the orders of the reactants are unknown, you can use the method described in a previous reply to determine what they are. A good example of doing all of these steps together can be found on problem 7 of the week 9&10 sapling assignment.

[305614361]

The order of a reaction is usually through experiments and I believe he also talks about in the week 9 lecture