Question

a)Assume the reaction 2Fe3+ + Sn2+ -> 2Fe2+ + Sn4+ has a rate law v = k[Fe3+][Sn2+]. If Fe2+ is produced at a rate of 0.12 mol L-1 s-1 when the reactant concentrations are 0.30 mol L-1 for Fe3+, and 0.40 mol L-1 for Sn2+, then what is the value of the rate constant, k ? Quote your answer to 2 decimal places.

Answer L.mol-1.s-1

b)

The half-life for the decomposition of a gaseous sample of thioketene, H₂C=C=S at 500 Pa is 42 s. When the thioketene pressure is 250 Pa the half-life is 21 s. Determine the order of the reaction, entering your answer as a number.

c)

At 1100 K, acetic acid decomposes via 2 competing, first order reactions:

CH₃COOH -> CH₄ + CO₂,   k₁ = 3.4 s^-1

CH₃COOH -> CH₂=C=O + H₂O,    k₂ = ? s^-1

The half life of acetic acid at this temperature is 0.10 s. What is the value of the rate constant, k₂?

d)

At 1100 K, acetic acid decomposes via 2 competing, first order reactions:

CH₃COOH -> CH₄ + CO₂,   k₁ = 4.1 s^-1

CH₃COOH -> CH₂=C=O + H₂O,    k₂ = ? s^-1

At 1100K, the yield of ketene (CH₂=C=O) is 71.5%. Estimate the rate constant, k₂, for the second reaction

e)

The following mechanism has been proposed for recombination of iodine atoms:

I + I -> I₂*, k₁ = [k1].0

I₂* -> I + I, k_-1 = [k-1].0

I₂* + M -> I₂, k₂ = [k2]

What is overall rate constant if k₁ = 4, k_-1 = 4 and k₂ = 0.04?

f)

The following mechanism has been proposed for recombination of iodine atoms:

I + I -> I₂*, k₁ = 9.0

I₂* -> I + I, k_-1 = 5.0

I₂* + M -> I₂, k₂ = 0.04

What is overall rate constant?

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Answer 1

(a) start by defining the reaction rate for this step can be written as Rate= -d[A]/dt=-d[B]/dt=+d[P]/dt

so the rate of formation of product d[P]/dt = k[A][B]

here 1/2 d[Fe²⁺]/dt = k [Fe³⁺][Sn²⁺]

                                                   1/2 x 0.12mol/L/s = k x 0.40mol/L x 0.30mol/L

                                                    k = 0.06/0.12 = 0.50 L.mol^-1.s^{-1 ( unit derivation = mol/L x 1/s x L/mol x L/mol = L/mol/s)}