Multiple Reactants

[Michelle Lee 2E]

Can someone please explain how we compare doubling initial concentration to how the initial rate changes, when finding the order of each reactant for multiple reactant reactions that is?
For example:
1) when we double the concentration and the initial rates are doubled
2) when we double the concentration and the initial rates are tripled
so on so forth.

[Justin Folk 3I]

1) Double reaction and initial rates are doubled:

let's pretend A --> B, [A] = c mol/L and rate = k [A]^1.
Your rate would be k*c^1 = kc

But let's say [A] = 2c, then rate would be k*(2c)^1 = 2kc

So for first order with respect to a reactant, doubling the concentration would give you double the rate

[Sarah Maraach 2K]

A good way to decide is to determine the type of relationship present in an equation. For example, if tripling the concentration causes a triple in rate, then you have a first order reaction because (3x)^1 = 3x. If this change causes an increase in rate by a factor of 9, then it’s a second order reaction because (3x)^2 = 9x. And of course if there is no change in rate then you have a zero order reaction since (3x)^0 = 1.