Question

Be sure to answer all parts. Carbon disulfide, a poisonous, flammable liquid, is an excellent solvent for phosphorus, sulfur, and some other nonmetals. A kinetic study of its gaseous decomposition reveals these data: Experiment Initial [CS2] (mol/L) Initial Rate (mol/L·s) 1 0.100 2.7 × 10−7 2 0.080 2.2 × 10−7 3 0.055 1.5 × 10−7 4 0.044 1.2 × 10−7 (a) Choose the rate law for the decomposition of CS2. Rate = k k[CS2] k[CS2]2 k[CS2]3 (b) Calculate the average value of the rate constant. Enter your answer in scientific notation. × 10 s−1

Answer 1

Explanation:

Experiment Initial [CS2] (mol/L) Initial Rate (mol/L·s)

1 0.100 2.7 × 10−7

2 0.080 2.2 × 10−7

3 0.055 1.5 × 10−7

4 0.044 1.2 × 10−7

a) Choose the rate law for the decomposition of CS2.

Comparing equations 1 and 3, reducing the initial concentration by almost half (from 0.100 to 0.055) leads too the rate of reaction to be reduced by almost half (from 2.7 × 10−7 to 1.5 × 10−7).

This signifies that the reaction is a first order reaction.

Rate = k [CS2]

(b) Calculate the average value of the rate constant.

Taking equation 1.

Rate = k [CS2]

k = Rate / [CS2]

k = 0.100 / (2.7 × 10−7)  = 0.037 x 10^8 = 3.7 x 10^6s-1