Question

How do you find the rate of reaction given the rate constant and concentrations if you don’t have the time?

Answer 1

You don't need the time. We take by convention the reaction rate as the initial rate `r_i(t) ~~ r(t)`, i.e. the rate at time zero,

`overbrace(r(t))^("rate") = overbrace(k)^"rate constants"overbrace([A]^m[B]^n)^" concentrations"`,

(where `m` and `n` are reaction orders with respect to each reactant, and `k` is the rate constant)

for the general reaction

`nu_A A + nu_B B -> nu_C C + nu_D D`,

where `nu` is the stoichiometric coefficient, `A` and `B` are reactants, and `C` and `D` are products.

The rest of the process depends on the problem, but this is usually where you would start, as the reaction rate usually decreases over time.