Title: CHE2FCB Kinetics Tutorial Quiz

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

I + I -> I_2*, k_1 = {k1}.0

I_2* -> I + I, k_-1 = {k-1}.0

I_2* + M -> I_2, k_2 = {k2}

What is overall rate constant?
A: {k1}/{k-1}*{k2} (formula; values not in the backup's text)
Feedback: Review Kinetics topic 4 (Mechanisms & complex reactions) - and in particular the section on pre-equilibrium approximation.

Q: The reaction X + Y -> 2Z is carried out in 200 mls of solution, with the rate of reaction 0.80 mol L^-1s^-1. How many mol of Z are produced in 1s? (Give your answer to 2 decimal places).

_______________ mol
A: 0.32
Feedback: General answer requirements - Only the value and not the units will be graded. - You must give your answer to 2 decimal places. To answer this question, the rate of consumption of X or Y must be compared to the rate of production of Z. That is, the reaction rate is given by rate = (-)1/n x d[X]/dt where n is the reaction stoichoimetry coefficient. The sign is negative for reactants and positive for products to ensure that the overall rate is positive in sign. Once the rate of production of Z is determined (units of mol/L/s), then the volume must be taken into account as it is less than a L.

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

CH_3COOH -> CH_4 + CO_2,   k_1 = {k1} s^-1

CH_3COOH -> CH_2=C=O + H_2O,    k_2 = ? s^-1

At 1100K, the yield of ketene (CH_2=C=O) is {y}%. Estimate the rate constant, k_2, for the second reaction.
A: ({k1}*{y})/(100-{y}) (formula; values not in the backup's text)
Feedback ("({k1}*{y})/(100-{y})"): Yield = k2 / (k1 + k2) Also need to take into account that the yield in the question is given as a percentage rather than a ratio as defined in the yield equation given here and in the notes.

Q: The rate constant, k, has units of mol^-2 L^2 s^-1

Enter the rate order as numbers (e.g. 0, 0.5, 1, 1.5, 2, 3...)
A: 3
Feedback ("3"): rate = k [A]^n where the units of rate are mol L^-1 s^-1. So, from the given units of k, the units of [A]^n can be determined.
Feedback: Review Kinetics topic 2 (Determination of rate laws) - and in particular the section on the initial rates method.

Q: The main reaction paths for the combustion of methane are shown below.

CH_4 + M -> CH_3 + H + M

CH_4 + X -> HX + CH_3

CH_3 + O_2 -> CH_2O + H

CH_2O + X -> CHO + HX

HCO + M -> H + CO + M

HCO + OH -> CO + H_2O

HCO + H -> CO + H_2

CO + OH -> CO_2 + H

H + O_2 -> OH + O

How many chain carriers are present according to this mechanism?
A: 6
Feedback ("6"): H, O, HO, HCO, CH_3, CH_2O
Feedback: Review Kinetics topic 5 (Chain reactions). First decide which species are chain carriers. Look for reactive intermediates that are produced and consumed.

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

CH_3COOH -> CH_4 + CO_2,   k_1 = {k1} s^-1

CH_3COOH -> CH_2=C=O + H_2O,    k_2 = ? s^-1

The half life of acetic acid at this temperature is {hl} s. What is the value of the rate constant, k_2?
A: -{k1}+(0.693147181/{hl}) (formula; values not in the backup's text)
Feedback ("-{k1}+(0.693147181/{hl})"): Revise section 4 - competing reactions. The half life is given by t_1/2 = ln(2) / k_eff where k_eff = k_1 + k_2. Rearrange to solve for k_2.
Feedback: Revise section 4 - competing parallel reactions.

Q: The half-life for the decomposition of a gaseous sample of thioketene, H_2C=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.
A: 0
Feedback: Review half-life equations for zero, first and second order reactions. Compare the relationship between t_1/2 and [A]_0.

Q: Assume the reaction 2Fe^3+ + Sn^2+ -> 2Fe^2+ + Sn^4+

has a rate law v = k[Fe^3+][Sn^2+].

If Fe^2+ is produced at a rate of 0.12 mol L^-1 s^-1 when the reactant concentrations are 0.30 mol L^-1 for Fe^3+, and 0.40 mol L^-1 for Sn^2+, then what is the value of the rate constant, k ? Quote your answer to 2 decimal places.

_______________ L.mol-1.s-1
A: 0.5
Feedback: Review Kinetics topic 1 (Introduction) - and don't forget to account for reactant and product stoichiometry. Recall that rate = (-)1/n x d[X]/dt where n is the reaction stoichiometry coefficient. The sign is positive for products and negative for reactants.

Q: The reaction A -> P has order 0.

Which of the following strategies would correctly yield the rate constant, k?
- plot [A] vs time, k = -gradient
- plot [A]^2 vs time, k = -gradient
- plot ln[A] vs ln[time], k = gradient
- plot ln[A] vs time, k = -gradient
- plot 1/[A] vs 1/time, k = -gradient
- plot 1/[A] vs time, k = -gradient
- plot 1/[A] vs time, k = gradient
- plot 1/[A]^2 vs time, k = -gradient
- plot [A] vs time, k = intercept
- plot ln[A] vs time, k = intercept
A: plot [A] vs time, k = -gradient
Feedback: The intehrated rate law needs to be rearranged in the form a a straight line equation: y = mx + c, where a plot of y against x will produce a gradient of m, and a y-intercept of c. For a zero-order reaction, the integrated rate law is [A]_t = [A]_0 - kt So plotting [A] against t will have a y-intercept of [A]_0, and a gradient of -k.

Q: The reaction A -> P has order 2.

Which of the following strategies would correctly yield the rate constant, k?
- plot [A] vs time, k = -gradient
- plot [A]^2 vs time, k = -gradient
- plot ln[A] vs ln[time], k = gradient
- plot ln[A] vs time, k = -gradient
- plot 1/[A] vs 1/time, k = -gradient
- plot 1/[A] vs time, k = -gradient
- plot 1/[A] vs time, k = gradient
- plot 1/[A]^2 vs time, k = -gradient
- plot [A] vs time, k = intercept
- plot ln[A] vs time, k = intercept
A: plot 1/[A] vs time, k = gradient

Q: The reaction A -> P has order 3.

Which of the following strategies would correctly yield the rate constant, k?
- plot [A] vs time, k = -gradient
- plot [A]^2 vs time, k = -gradient
- plot ln[A] vs ln[time], k = gradient
- plot ln[A] vs time, k = -gradient
- plot 1/[A] vs 1/time, k = -gradient
- plot 1/[A] vs time, k = -gradient
- plot 1/[A] vs time, k = gradient
- plot 1/[A]^2 vs time, k = - 0.5 x gradient
- plot [A] vs time, k = intercept
- plot ln[A] vs time, k = intercept
- plot 1/[A]^2 vs time, k = 0.5 x gradient
A: plot [A] vs time, k = -gradient

Q: The reaction A -> P has order 1.

Which of the following strategies would correctly yield the rate constant, k?
- plot [A] vs time, k = -gradient
- plot [A]^2 vs time, k = -gradient
- plot ln[A] vs ln[time], k = gradient
- plot ln[A] vs time, k = -gradient
- plot 1/[A] vs 1/time, k = -gradient
- plot 1/[A] vs time, k = -gradient
- plot 1/[A] vs time, k = gradient
- plot 1/[A]^2 vs time, k = -gradient
- plot [A] vs time, k = intercept
- plot ln[A] vs time, k = intercept
A: plot ln[A] vs time, k = -gradient

Q: In a chain polymerization reaction, what would be the expected outcome if both initiator and monomer concentrations were halved?
- Propagation rate decreases to 50%, chain size decreases to 50% of initial values
- Propagation rate decreases to 71%, chain size decreases to 71% of initial values
- Propagation rate decreases to 35%, chain size decreases to 71% of initial values
- Propagation rate decreases to 50%, chain size increases to 141% of initial values
- Propagation rate increases to 71%, chain size increases to 141% of initial values
A: Propagation rate decreases to 35%, chain size decreases to 71% of initial values

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

I + I -> I_2*, k_1 = [k1].0

I_2* -> I + I, k_-1 = [k-1].0

I_2* + M -> I_2, k_2 = [k2]

What is overall rate constant if k_1 = {k1}, k_-1 = {k-1} and k_2 = {k2}?
A: {k2}*{k1}/{k-1} (formula; values not in the backup's text)
Feedback: Review Kinetics topic 4 (Mechanisms & complex reactions) - and in particular the section on pre-equilibrium approximation.

Q: A plot of 1/[ClO^-] vs time is given for the reaction 3ClO^- -> ClO_3^- + 2Cl^- with gradient [m], intercept [c]. What  is the rate constant k ?

[Image]
- c
- m
- 2m
- 3m
- m/2
- m/3
A: m/3

Q: In a chain polymerization reaction, what would be expected if the initiator concentration is increased by a factor 4?
- Propagation rate increases by factor 4, chain size decreases by factor 4.
- Propagation rate increases by factor 2, chain size decreases by factor 2.
- Propagation rate increases by factor 4, chain size increases by factor 2.
- Propagation rate increases by factor 4, chain size increases by factor 4.
- Propagation rate decreases by factor 2, chain size decreases by factor 2.
A: Propagation rate increases by factor 2, chain size decreases by factor 2.

Q: The reaction H_2 + Br_2 -> 2HBr is believed to follow the mechanism shown below.

Br· + H_2 -> HBr + H

H· + Br_2 -> HBr + Br

Br·+ Br· + M -> Br_2 + M

Br_2 + M -> Br· + Br· + M   (M= H_2 or Br_2)

H· + HBr -> H_2 + Br

How many chain carriers are present according to this mechanism?
A: 2
Feedback: Review Kinetics topic 5 (Chain Reactions)

Q: The reaction H_2 + Br_2 -> 2HBr is believed to follow the mechanism shown below. Label each of following steps as i (for initiation), p (for propagation), b (for branching) or t (for termination).
- Br· + H_2 -> HBr + H | p
- H· + Br_2 -> HBr + Br | p
- Br·+ Br· + M -> Br_2 + M | t
- Br_2 + M -> Br· + Br· + M (M= H_2 or Br_2) | i
- H· + HBr -> H_2 + Br | r
Feedback: Review Kinetics topic 5 (Chain Reactions)

Q: Consider the following mechanism comprised of elementary reactions:

2A -> B ... k_1

A + B -> A + C ... k_2

What is correct expression for d[B]/dt ?
- -k_1[A]^2 + k_2[A][B]
- 2k_1[A]^2 - k_2[A][B]
- k_1[A]^2 - k_2[A][B]
- 2k_1[A] - k_2[A][B]
- k_1[A] + k_2[A][B]
A: k_1[A]^2 - k_2[A][B]

Q: Consider the following mechanism comprised of elementary reactions:

2A -> B ... k_1

C + B -> 2B ... k_2

What is correct expression for d[B]/dt ?
- -2k_1[A]^2 - k_2[C][B]
- k_1[A]^2 + k_2[C][B]
- 2k_1[A]^2 + k_2[C][B]
- -k_1[A] - k_2[C][B]
- 2k_1[A]^2 + 2k_2[C][B
A: k_1[A]^2 + k_2[C][B]

Q: Consider the following mechanism comprised of elementary reactions:

2A -> B ... k_1

A + B -> A + C ... k_2

What is correct expression for d[A]/dt ?
- -2k_1[A]^2 - k_2[A][B]
- -2k_1[A]^2
- 2k_1[A]^2 + k_2[A][B]
- k_1[A]^2
- -2k_1[A]
A: -2k_1[A]^2

Q: Consider the following mechanism comprised of elementary reactions:

A + B -> C ... k_1

C -> A + B ... k_-1

C + B -> C + D ... k_2

A+ 2C -> E + A ... k_3

What is correct expression for d[C]/dt ?
- k_1[A][B] + k_-1[C]^2 - k_2[C][B] - k_3[A][C]^2
- k_1[A][B] - k_-1[C]^2 - k_2[C][B] - 2k_3[A][C]^2
- k_1[A][B] -k_-1[C] - 2k_3[A][C]^2
- -k_1[C] +k_-1[C] - k_2[C][B] - k_3[A][C
- k_1[A][B] +k_-1[C]^2 + k_3[A][C]^2
A: k_1[A][B] -k_-1[C] - 2k_3[A][C]^2

Q: Consider the following mechanism comprised of elementary reactions:

A + B -> 2C ... k_1

2C -> A + B ... k_-1

C + 2A -> D + A ... k_2

C + B -> C + E ... k_3

What is correct expression for d[C]/dt ?
- k_1[A][B] -2k_-1[C]^2 - k_2[C][A] + k_3[C][B]
- 2k_1[A][B] -2k_-1[C]^2 - k_2[C][A]^2
- k_1[A][B] -k_-1[C]^2 - k_2[C][A]^2 + k_3[C][B]
- 2k_1[C]^2 -2k_-1[C]^2 + k_2[C][A]^2 - k_3[E][C]
- k_1[A][B] +k_-1[C]^2 + k_2[C][A]^2
A: 2k_1[A][B] -2k_-1[C]^2 - k_2[C][A]^2

Q: Consider the following mechanism comprised of elementary reactions:

A + B -> 2C ... k_1

2C -> A + B ... k_-1

C + 2A -> D + A ... k_2

D + B -> 3B ... k_3

What is correct expression for d[B]/dt ?
- k_1[A][B] – k_-1[C]^2 + 3k_3[D][B]
- –k_1[A][B] + k_-1[A][B] - k_3[D][B]
- –k_1[A][B] + 2k_-1[C]^2 - 2k_3[D][B]
- –k_1[A][B] + k_-1[C]^2 + 2k_3[D][B]
- k_1[A][B] + k_-1[C]^2 + k_3[D][B]
A: –k_1[A][B] + k_-1[C]^2 + 2k_3[D][B]

Q: Consider the following mechanism comprised of elementary reactions:

A + B -> 2C ... k_1

2C -> A + B ... k_-1

C + 2A -> D + A ... k_2

D + B -> E + C ... k_3

What is correct expression for d[A]/dt ?
- k_1[A][B] – k_-1[C]^2 + k_2[C][A]
- –k_1[A][B] + 2k_-1[C]^2 - 2k_2[C][A]^2
- k_1[A][B] + k_-1[C]^2 + 2k_2[C][A]^2
- –k_1[A][B] + k_-1[C]^2 - k_2[C][A]^2
- –k_1[A][B] + k_-1[A][B] - k_2[C][A]^2
A: –k_1[A][B] + k_-1[C]^2 - k_2[C][A]^2

Q: Match the following descriptions with their methods.
- With all reactants except one in large excess, their concentrations are effectively constant during the experiment | Isolation method
- The reaction commences using chemically equivalent concentrations of reactants | Stoichiometric method
- A differential method in which starting concentrations are systematically varied | Initial rates method
- The equilibrium of a reaction is disturbed by a rapid change in temperature or pressure to allow determination of rate constants for forward and backward reactions | Relaxation method
- Broadening of spectroscopic transitions is measured to provide an indication of rate constants – applying the Heisenberg Uncertainty Principle | Lifetime measurement

Q: A plot of 1/[ClO^-] vs time is given for the reaction 3ClO^- -> ClO_3^- + 2Cl^- with gradient [m], intercept [c]. What is the rate order,

(NEED TO GET THIS PLOT!!)
A: 2nd order / Second order

Q: The following plot has been obtained for the reaction A -> P.

What order is the reaction?

[Image]
- Zero order
- 1st order
- 2nd order
A: 2nd order
Feedback: Review Kinetics topic 2 (Determination of rate laws) - and in particular the graphical summary in integral methods.

Q: The following plot has been obtained for the reaction A -> P.

What order is the reaction?

[Image]
- Zero order
- 1st order
- 2nd order
A: 1st order
Feedback: Review Kinetics topic 2 (Determination of rate laws) - and in particular the graphical summary in integral methods.

Q: The following plot has been obtained for the reaction A -> P.

What order is the reaction?

[Image]
- Zero order
- 1st order
- 2nd order
A: Zero order
Feedback: Review Kinetics topic 2 (Determination of rate laws) - and in particular the graphical summary in integral methods.

Q: If a reaction has an overall order of 1/2, what are the appropriate units for the rate constant?
- mol L^-1 s^-1
- mol^0.5 L^-0.5 s^-1
- s^-1
- mol^-0.5 L^0.5 s^-1
- mol^-1 L s^-1
- mol^-2 L^2 s^-1
A: mol^0.5 L^-0.5 s^-1
Feedback: Try dimensional analysis using rate, ν = k [concentration]^n where n is the reaction order.

Q: Label each of following main reaction paths for the combustion of methane with a single letter: i (for initiation), p (for propagation), b (for branching) or t (for termination).
- CH_4 + X -> HX +CH_3 | p
- CH_3 + O_2 -> CH_2O + H | p
- CH_4 + M -> CH_3 + H + M | i
- CH_2O + X -> CHO + HX | p
- HCO + M -> H + CO + M | p
- HCO + OH -> CO + H_2O | t
- HCO + H -> CO + H_2 | t
- CO + OH -> CO_2 + H | p
- H + O_2 -> OH + O | b
Feedback: Review Kinetics topic 5 (Chain reactions). First decide which species are chain carriers. Look for reactive intermediates that are produced and consumed.