Rate law of reactions, what about the proportions?
[OP, in a comment] oh ok, so if we double the amount of only one substance, that substance will get left?


Yes. The rate law tells you how fast product is being made. The change in the different species is still given by the chemical reaction equation (which tells you in which proportion the amount of species will change, not in which proportion they are present at the beginning or at the end of the reaction).

You can see that when you look at the definition of rate:

$$\mathrm{rate} = \frac{d[X_i]}{\nu_i dt}$$

where $\nu_x$ is the (signed, i.e. negative for reactants) stoichiometric factor of the $i$-th species. Dividing by the stoichiometric factor ensures that the law of definite proportions is followed.


  [OP in another comment] we cant simply put more of a substance to get more of the product, the reactants must have a fixed ratio.


The law of definite proportions is not about the amounts present, but about the change in those amounts. I can set up a reaction with 1000 times more elemental oxygen than hydrogen, but they will still react in a 1:2 ratio if the reaction yields water.