Question

Reaction Rates: Predicting Changes in Concentration We can often predict the change in concentration for some component in the reaction by watching how another species is changing. In the following reaction, molecules of the product are appearing at a faster rate than molecules of the reactant are being consumed. N2O4 (g) → 2 NO2 (g) This is why we scale the rate to the stoichiometry of the reaction. We can express the rate for a reaction with respect to any of the species present, based on the stoichiometry. rate = - Δ[N2O4]/Δt = 1/2 Δ[NO2]/Δt Use the stoichiometry of the reaction to predict the missing entry in the following table: Time [N2O4] [NO2] 0.0000 0.050 0.000 20.000 0.033 ? M

Answer 1

ANSWER : 0.034 M

Consider a reaction N₂O_4(g) 2 NO_2(g)

The rate of above reaction is given as Rate = -   N₂O₄ / t =( 1/2 )  NO₂ / t

Here   N₂O₄ = 0.05 - 0.033 = 0.017 M

   t = 20

Hence Rate= 0.017/20=8.5x 10^-4 M/s

putting these values in rate equation we get ( 1/2 )  NO₂ / t = 8.5x 10^-4  

   ( 1/2 )   NO_{2 =} 8.5x 10^-4 x   t=8.5x 10^-4 x 20

= 0.017  

    NO₂= 0.017 x 2

= 0.034 M