Nitric oxide and nitrogen dioxide are found in photochemical smog. Nitrogen dioxide is formed from nitrogen monoxide in the exhaust of automobile engines. A possible mechanism for this reaction is given below. What is the rate law predicted by the mechanism?

Reaction:
2NO(g) + O2(g) → 2NO2(g)
Step 1 (fast): NO + NO → N2O2
Step 2 (slow): N2O2 + O2 → 2NO2

A. Rate = k[NO]2
B. Rate = k[NO2]2
C. Rate = k[NO][O2]
D. Rate = k[NO]2[O2]
E. Rate = k[No2]^2/[No]^2[o2]

(D) Rate = k[NO]²[O₂]

Explanation:

The rate law predicted by the mechanism

     Reaction:

                                                  2 NO(g) + O₂(g) →2 NO₂(g)

                                                 Step 1 (fast): NO + NO → N₂O₂

                                               Step 2 (slow): N₂O₂ + O₂ → 2 NO₂

According to rate law

                        rate of reaction is measured from slowest step

                                    ------------------  (i)

Since N₂O₂ is an intermediate

   So we replace intermediate from rate law equation

                                         From step 1 we can write

From equation (i)      

                        ∴   Rate = k[NO]²[O₂]

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2