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Ch.14 - Chemical Kinetics
All textbooksTro 4th EditionCh.14 - Chemical KineticsProblem 107
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Chapter 14, Problem 107

What rate law corresponds to the proposed mechanism for the formation of hydrogen bromide, which can be written in a simplified form as: Br2(g) → 2Br(g) (Fast) Br(g) + H2(g) → HBr(g) + H(g) (Slow) H(g) + Br2(g) → HBr(g) + Br(g) (Fast)?

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1
Identify the slow step in the mechanism, as it determines the rate law. In this case, the slow step is: Br(g) + H2(g) → HBr(g) + H(g).
Write the rate law based on the slow step. The rate law is determined by the reactants in the slow step: rate = k[Br][H2].
Recognize that the concentration of Br is not typically known, so we need to express it in terms of known quantities.
Use the fast equilibrium step to express [Br] in terms of [Br2]. The fast step is: Br2(g) ⇌ 2Br(g).
Assume the fast step reaches equilibrium quickly, allowing us to use the equilibrium expression: [Br]^2 = K[Br2], where K is the equilibrium constant. Solve for [Br] and substitute into the rate law.
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Textbook Question

Consider the gas-phase reaction: H2(g) + I2(g) → 2 HI(g) The reaction was experimentally determined to be first order in H2 and first order in I2. Consider the proposed mechanisms. Proposed mechanism I: H2(g) + I2(g) → 2 HI(g) Single step Proposed mechanism II: I2(g) Δk1k-12 I(g) Fast H2( g) + 2 I( g) → k22 HI( g) Slow a. Show that both of the proposed mechanisms are valid.

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Textbook Question

Consider the gas-phase reaction: H2(g) + I2(g) → 2 HI(g) The reaction was experimentally determined to be first order in H2 and first order in I2. Consider the proposed mechanisms. Proposed mechanism I: H2(g) + I2(g) → 2 HI(g) Single step Proposed mechanism II: I2(g) Δk1k-12 I(g) Fast H2( g) + 2 I( g) → k22 HI( g) Slow b. What kind of experimental evidence might lead you to favor mechanism II over mechanism I?

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Textbook Question

Consider the reaction: 2 NH3(aq) + OCl-(aq) → N2H4(aq) + H2O(l) + Cl- (aq) This three-step mechanism is proposed: NH3(aq) + OCl- (aq) Δk1k2 NH2Cl(aq) + OH- (aq) Fast NH2Cl(aq) + NH3(aq) →k3 N2H5+ (aq) + Cl- (aq) Slow N2H5+ (aq) + OH-(aq) →k4 N2H4(aq) + H2O(l) Fast a. Show that the mechanism sums to the overall reaction.

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Open Question
What rate law corresponds to the proposed mechanism for the formation of hydrogen iodide, which can be written in simplified form as: I2 Δk1k-1 2I (Fast), I + H2 Δk2k-2 H2I (Fast), H2I + I ¡k3 2HI (Slow)?
Textbook Question

A certain substance X decomposes. Fifty percent of X remains after 100 minutes. How much X remains after 200 minutes if the reaction order with respect to X is (c) second order?

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Textbook Question

The half-life for radioactive decay (a first-order process) of plutonium- 239 is 24,000 years. How many years does it take for one mole of this radioactive material to decay until just one atom remains?

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