[ampakine]

The question is:

The reaction CO(g) + NO₂(g)   3CO₂(g) + NO(g)
follows the rate law, rate = k[NO₂]²

Determine the proportional change in the rate resulting from each of
the following alterations:
      (i) the pressure of NO₂ is decreased from 0.60 to 0.20 atm;
      (ii) the CO concentration is increased from 0.01 to 0.04 M;
      (iii) the temperature is increased from 300 to 400K.

I can see this reactions 2nd order with respect to NO₂ and 0th order with respect to CO so for (i) I'm guessing the rate will decrease 3² fold and for (ii) I'd say theres no change in rate because its zeroth order with respect to CO but I don't know how to do (iii). Would you say they expect you to use the approximation that "rate doubles for every 10C increase in temperature"? Since they don't actually give you the rate or rate constant you can't use the Arrhenius equation here can you?

[Schrödinger]

You're just going to find out the ratio of rate at 400K to the rate at 300K... You don't need the Arrhenius constant. It'll get canceled anyway. Go ahead with the Arrhenius equation for (iii)

You're right about parts i and ii