Cliffs AP Chemistry, 3rd Edition

Samples: Free-Response Questions

1. The reaction
   2 NO 2 (g) + Cl 2 (g) →2 NO 2 Cl(g)

was studied at 20°C and the following data were obtained:

Experiment Initial [NO 2 ] Initial [Cl 2 ] Initial Rate of Increase

(mole ⋅ liter–1) (mole ⋅ liter–1) of [NO 2 Cl]

(mole ⋅liter–1⋅sec–1)

1 0.100 0.005 1.35 × 10 –7

2 0.100 0.010 2.70 × 10 –7

3 0.200 0.010 5.40 × 10 –7

(a) Write the rate law for the reaction.

(b) What is the overall order for the reaction? Explain.

(c) Calculate the rate-specific constant, including units.

(d) In Experiment 3, what is the initial rate of decrease of [Cl 2 ]?

(e) Propose a mechanism for the reaction that is consistent with the rate law expression

you found in part (a).

Answer

1. Given: 2 NO 2 (g) + CO 2 (g) →2 NO 2 Cl(g)
   (a) Restatement: Rate law.
   rate = k[NO 2 ]n[Cl 2 ]m

Expt. 1: rate = 1.35 × 10 –7mole/liter ⋅sec

= k(0.100 M)n(0.0050 M)m

Expt. 2: rate = 2.70 × 10 –7mole/liter ⋅sec

= k(0.100 M)n(0.010 M)m

Expt. 3: rate = 5.40 × 10 –7mole/liter ⋅sec

= k(0.200 M)n(0.010 M)m

./

./

1

2

135 10

270 10

rate

rate

mole liter sec

mole liter sec

7

7

#:

= #:

..

..

k

k

0 100 0 0050

0 100 0 010

MM

MM

nm

nm

=

^^

^^

hh

hh

= 2.00 = (2.0)mm= 1

Kinetics