Question

Part A - Calculating an Average Rate of Reaction

If the experiment below is run for 60 s, 0.16 mol A remain. Which of the following statements is or are true?

I. After 60 s there are 0.84 mol B in the flask.

II. The decrease in the number of moles of A from t1 = 0 to t2 = 20 s is greater than that for t1 = 40 to t2 = 60 s.

III. The average rate for the reaction from t1 = 40 to t2 = 60 s is 7.0×10−3 M/s.

A) Only one of these statements is true

B) Statements I and II are true

C) Statements I and III are true

D) Statements II and III are true

E) All three statements are true

Answer 1

ANSWER IS E

                    A ----------------------> B

Initial concentration of A =    t=0 sec      1 mole                          0         

                                             t=20sec         0.54                                  0.46

                                             t= 40 sec        0.30                                0.24

                                             t=60                 0.16                                  0.14

1) after 60 seconds   [B] =[0.46+0.24+0.14]

                                            = 0.84   TRUE

2) t= 0   to    t=20      Decrease in no of mole of      A = 0.46

     t= 20   to    t=40      Decrease in no of mole of      A = 0.24

                   STATEMENT 2 ALSO TRUE

3) Rate = - [ 0.24-046]/[40-20]

                  = 7x10^-3 seconds   

                  = statement 3 also true

All the statements are true