Question

The gas-phase reaction between NO and Br is represented by the equation
2NO (g) + Br₂ (g) → 2NOBr (g)
Write the expressions for the rate of consumption of reactants and formation of products.

Answer 1

For the reaction says, aA + bB -- cC + dD,

The rate of reaction will for the D production will be as follows,

Rate (A) = -a/d rate (1)

Rate (B) = -b/d rate (1)

Rate © = c/d rate (1)

Rate of NOBr = -2/1 Rate(1) which will be the actual answer.  

Answer 2

The rate expression is derived by step II of the mechanism, as it is the slower one. <br> Rate

=K[NOBr2][NO]…(1)

is an intermediate and thus its concentration should be replaced from equation (1). For step (I) Equilibrium constant

NOBr2

is an intermediate and thus its concentration should be replaced from equation (1). For step (I) Equilibrium constant

[NOBr2]=Kc[NO][Br2]...(2)

Thus by eqs. (1) and (2) <br> Rate=

K'[NO]2[Br2]