help Model 3: Second-order kinetics Characteristics If the concentretion of a re

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help Model 3: Second-order kinetics Characteristics If the concentretion of a reactant is doubled, the rate quadruples At 2x the first half-life, the [A] remaining is 33% Integrated rate law Slope k time 5. At 25 C in CCl solvent, the reaction is second order in the c 1.64x 10a L/mol sSuppose the their concentration after 20 × 10's ssecond order the concentration of iodine atoms. The rate constont k has been measured as o L/mol s. Suppose the initial concentration of iodine atoms is 100 x 10* M. Calculate 6. The forward rate for the reaction Ce (oq) Fe (ag)Ce' (aq) Fe (ag) is first order in [Cet Jand [Fe -1.and second order overall. The rate constant k has been determined to be 1.00 x 10' L/mol s at 25 C. In an experiment, 100.00 ml of 0010 M Ce(SO.)2 solution is mixed rapidly with 100.00 ml Of 0.010 M FesO4 solution and allowed to react. Calculate the concentration of Ce remaining after 2.0 seconds. (NOTE: You my assume that Ce" and Fe are consumed at the same rate (1:1), so use the integrated second-order rate law expression in your calculation.) ior she to

Explanation / Answer

5. 1/[A] = 1/[Ao] + kt

where,

[Ao] = 1 x 10^-4 M

[A] = unknown

k = 1.64 x 10^10 L/mol.s

t = 2 x 10^-6 s

Feed values,

1/[A] = 1/1 x 10^-4 + 1.64 x 10^10 x 2 x 10^-6

[A] = 2.34 x 10^-5 M

6. moles of Ce(SO4)2 = molarity x volume = 0.01 x 0.1 = 0.001 mols

moles of FeSO4 = 0.01 x 0.1 = 0.001 mols

So, 0.001 mols of FeSO4 would react with 0.0005 mols of Ce(SO4)2

moles of Ce(SO4)2 remaining = 0.0005 mols

So, molarity of Ce(SO4)2 remaining = 0.0005/0.2 = 0.0025 M

Feed values,

1/[A] = 1/0.0025 + 1 x 10^3 x 2

[A] = 4.17 x 10^-4 M of Ce4+ remaining after 2 sec

3. the rate law is consistent with the mechanism shown in (ii)

a. the rate law becomes,

rate = k[NO]^2[O2]

b. In mechanism 1, the slow step is step 2

c. rate law for this step is,

rate = k[NO][NO3]

NO3 is the intermediate.

let k2 and k-1 be the rate constants for this step then,

k2[NO][NO3] = k-2[NO2]^2

[NO3] = (k-2/k2)[NO]/[NO2]^2

Feed in above equation

rate = k2.k-2/k2[NO]^2[NO]/[NO2]^2 = k-2[NO]^3/[NO2]^2

d. the rate of a reaction is determined by the slow step,

as we see here, rate = k[NO]^2

which is different then actual rate law,

rate = [NO]^2[O2]

Thus this does not satisfies the rate observed for the reaction.

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