Question

From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants. (i) 3 NO(g) → N2O (g) Rate = k[NO]2 (ii) H2O2 (aq) + 3 I− (aq) + 2 H+ → 2 H2O (l) + Rate = k[H2O2][I−] (iii) CH3CHO(g) → CH4(g) + CO(g) Rate = k [CH3CHO]3/2 (iv) C2H5Cl(g) → C2H4(g) + HCl(g) Rate = k [C2H5Cl]

Answer 1

H2O2 (aq) + 3 I− (aq) + 2 H+ → 2 H2O (l) + Rate = k[H2O2][I−] (iii) CH3CHO(g) → CH4(g) + CO(g) Rate = k [CH3CHO]3/2 (iv) C2H5Cl(g) → C2H4(g) + HCl(g) Rate = k [C2H5Cl]

Answer 2

Explanation:

1. Rate = k[NO]2 (Given)

Order of the reaction = 2

Dimension of k = Rate / [NO]2

= mol L-1 s-1 / (mol L-1)2

= L mol-1 s-1

 

2. Rate = k[H2O2][I - ] (Given)

Order of the reaction = 2

Dimension of k = Rate  / [H2O2][I - ]

= L mol-1 s-1

 

3. Rate =k [CH3CHO]3/2 (Given)

Therefore, order of reaction = 3/2

Dimension of k = Rate / [CH3CHO]3/2

=  mol L-1 s-1   / (mol L-1)3/2

= mol L-1 s-1   / mol3/2  L-3/2

= L½ mol-½  s-1

 

4. Rate = k [C2H5Cl] (Given)

Order of the reaction = 1

Dimension of k = Rate /  [C2H5Cl]

= mol L-1 s-1   / mol L-1

= s-1