Question

At a certain time in a reaction, substance A is disappearing at a rate of 4.0×10^−2 M/s, substance B is appearing at a rate of 2.0×10^−2 M/s, and substance C is appearing at a rate of 6.0×10^−2 M/s. Which of the following could be the stoichiometry for the reaction being studied?

A.) A → 2 B + 3 C

B.) A + 2 B → 3 C

C.) 2 A + B → 3 C

D.) 2 A → B + 3 C

E.) 4 A → 2 B + 3 C

Answer 1

Let the reaction be

given

A is disappearing

and

both B and C are appearing

so

A is reactant and B,C are products

so

Let the reaction be

aA ---> bB + cC

now

accordint to stoichiometry

( -d[A] /dt) / a = ( d[B]/dt) / b = ( d[C]/dt) / c

given

-d[A]/dt = 4 x 10-2

d[B]/dt = 2 x 10-2

so

4 x 10-2 / a = 2 x 10-2 / b

2b = a

now

given

d[C]/dt = 6 x 10-2

so

4 x 10-2 / a = 6 x 10-2 / c

2c = 3a

a = 2c/3

so

we get

a = 2b = 2c/3

let b=1

then

a = 2b = 2 x 1 = 2

c = 3b = 3 x 1= 3

so

the equation becomes

2A ---> B + 3C

so

the answer is D) 2A --> B + 3C