Comparing experiments to find order rxn

[Keirsten Andersen 3L]

When comparing three experiments to determine the order of reaction, when do you compare 1 to 2 and 2 to 3 vs comparing 1 to 2 and 1 to 3, as the book does?

[Helen Meng 2J]

I think when you are comparing experiments to find the reaction order, you look for when concentrations are held constant. For example, if you have three reactants: A, B and C, and you want to find the reaction order for reactant B, you have to look for two experiments where both reactants A and C have concentrations that are held constant. If that happens to be when comparing experiment 1 and 2, then you would use those two experiments. If that happens to be when comparing experiment 1 and 3, then you would you those, and so on. So it doesn't really matter which experiments you compare as long as all but one of the reactants have concentrations that are held constant. Then you can find the reaction order of that reactant that doesn't have a concentration that is held constant. Hope this helps!

[Chem_Mod]

Helen is correct, generally you want to compare two experiments where only one variable has a different value. It follows the design of basic experimentation where you you manipulate an independent variable to observe changes in an outcome while keeping all other factors constant so you are sure that the changes you are making are determining the results. If you have variables X, Y, and Z and you are comparing two experiments where X and Y are both different this can be a little more difficult. But if you have information on how the rate changes if one variable, say X, changes, then you can factor the influence of X in when considering how Y changes the rate.