Discuss with your group the data in the table below and answer the following que
ID: 591687 • Letter: D
Question
Discuss with your group the data in the table below and answer the following questions. Before you write down the answers, m]ake sure that everybody in your group understands how to predict reaction rates from such data. aA + bB cC + dD Experiment # (all at 298K) Initial Rate Initial concentration Initial concentration mol/(L-hr) [Alo B]o 0.50 × 10-2 0.50 × 10-2 0.50 × 10-2 1.00 x 10-2 1.50 × 10-2 0.50 0.75 1.00 0.50 0.50 0.20 0.20 0.20 0.40 0.60 a) Without doing any calculation can you predict the order of reaction with respect to A? the order of the reaction with respect to B? the overall reaction order? b) If [Alo is halved what will happen to the initial reaction rate? c) If [Bo is halved what will happen to the initial reaction rate? d) Now work out the units for rate constant for this reactionExplanation / Answer
a) As given in the data , keeping the concentration of B constant, when the concentration of A increase by two times no change in the rate of the reaction remains unchanged.
from, expt 1 and 3 : [A]o = 0.50 mol/ L, [B]o = 0.20 mol/ L , Rate = 0.50 x 10-2 (mol/ L.H)
[A]o = 1.0 mol/ L, [B]o = 0.20 mol/ L , Rate = 0.50 x 10-2 (mol/ L.H)
hence, the rate of reaction is independent of the concentration of A i.e.- reaction is zero order w.r.t A
on the otherhand, keeping the concentration of A constant, when the concentration of B increases by two times, the rate of reaction also increases by two times.
from, expt 1 and 4 :
[A]o = 0.50 mol/ L, [B]o = 0.20 mol/ L , Rate = 0.50 x 10-2 (mol/ L.
[A]o = 0.50 mol/ L, [B]o = 0.40 mol/ L , Rate = 1.0x 10-2 (mol/ L.H)
This indicates that a linear relationship exist among the concentration of B and that of the rate of reaction. Thus, reaction is 1st order wrt B
so, overall order = order wrt A + order wrt B = 0+1=1 i.e.- 1st order
b) The order wrt A is zero order i.e.- order of the reaction is independent of the concentration of A. Hence, when the concentration of A is halved, no change in the initial rate of reaction is observed.
c) order wrt to B is 1st order and hence there exist a linear relationship between them. Thus, when the concentration of B is halved, the rate of reaction also decreases to half of its value.
d) The overall order of the reaction is 1st order
the general representation of unit of rate constant is given by, (mol/L)1-n (time)-1, where, n = order of reaction
in the given question time is expressed in hour and n = 1 (1st order )
thus, unit for rate constant will be, (mol/L)1-1 (hour)-1 = (hour)-1