Determining Rate Equations

Run X Y ZInitial Rate

moldm-3s-1

1 0.1 0.1 0.1 2.4 x 10-3

2 0.1 0.1 0.3 7.2 x 10-3

3 0.05 0.1 0.1 2.4 x 10-3

4 0.1 0.4 0.1 3.84 x 10-2

x 3 x 3

• Rate is proportional to change [Z]

• Rate 1st order w.r.t. Z

• Rate = k [Z] so far

Run X Y ZInitial Rate

moldm-3s-1

1 0.1 0.1 0.1 2.4 x 10-3

2 0.1 0.1 0.3 7.2 x 10-3

3 0.05 0.1 0.1 2.4 x 10-3

4 0.1 0.4 0.1 3.84 x 10-2

/ 2

• Concentration of X halved• Rate unchanged• Rate zero order w.r.t. X

• Rate = k [Z] so far (X term omitted)

Run X Y ZInitial Rate

moldm-3s-1

1 0.1 0.1 0.1 2.4 x 10-3

2 0.1 0.1 0.3 7.2 x 10-3

3 0.05 0.1 0.1 2.4 x 10-3

4 0.1 0.4 0.1 3.84 x 10-2

x 4

•Concentration of Y x 4

•Rate x 16 (42)

•Rate 2nd order w.r.t. Y

•Rate = k [Z] [Y]2

x 16

Deduce order w.r.t. A & B. Write rate equation & then calculate ?

Run A BInitial Rate

moldm-3s-1

1 0.2 0.3 1.6 x 10-4

2 0.2 0.6 3.2 x 10-4

3 0.4 0.6 1.28 x 10-3

4 0.5 0.3 ?

• [B] x2 and Rate x2

• Reaction is 1st order w.r.t. [B]

• Rate = k [B]

Deduce order w.r.t. A & B. Write rate equation & then calculate ?

Run A BInitial Rate

moldm-3s-1

1 0.2 0.3 1.6 x 10-4

2 0.2 0.6 3.2 x 10-4

3 0.4 0.6 1.28 x 10-3

4 0.5 0.3 ?

•[A] x2 and Rate x4 (22)

•Reaction is 2nd order w.r.t. [A]

•Rate = k [B] [A]2

Deduce order w.r.t. A & B. Write rate equation & then calculate ?

Run A BInitial Rate

moldm-3s-1

1 0.2 0.3 1.6 x 10-4

2 0.2 0.6 3.2 x 10-4

3 0.4 0.6 1.28 x 10-3

4 0.5 0.3 ?

• [A] x2 and [B] x2

• Rate x8 (23)

• This means overall order is 3

• Rate = k [B] [A]2

Rate = k [A]2 [B]

Run A BInitial Rate

moldm-3s-1

1 0.2 0.3 1.6 x 10-4

2 0.2 0.6 3.2 x 10-4

3 0.4 0.6 1.28 x 10-3

4 0.5 0.3

x 2.5x2.52

x6.5

1.0 x 10-3

Rate = k [X]2 [Y]

Run Y XInitial Rate

moldm-3s-1

1 0.2 0.2 1.2 x 10-4

2 0.4 0.4 9.6 x 10-4

3 0.4 2.4 x 10-4

4 0.6 0.3 b

./. 4./. 4

0.1

Rate = k [X]2 [Y]

Run Y XInitial Rate

moldm-3s-1

1 0.2 0.2 1.2 x 10-4

2 0.4 0.4 9.6 x 10-4

3 0.4 2.4 x 10-4

4 0.6 0.3

x1.5x30.1

x 6.75

x 1.52 x 3

8.1 x 10-4