How Does the Reaction Progress Affect Rate in a Second-Order Redox Reaction?

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Discussion Overview

The discussion revolves around the kinetics of a second-order redox reaction involving nitrogen dioxide (NO2) and carbon monoxide (CO). Participants are examining the relationship between initial concentrations and reaction progress, specifically how the rate changes from the initial state to 50% completion.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant states that the initial concentration of NO2 is twice that of CO, leading to a specific stoichiometric relationship.
  • Another participant questions the derivation of the concentrations at 50% completion, specifically the values of 1/2[CO]i and 0.75[NO2]i.
  • A participant requests mathematical clarification on how the concentration of NO2 can be 0.75[NO2]i at 50% completion, suggesting a misunderstanding of the stoichiometry involved.
  • One participant attempts to clarify that if half of the CO has reacted, the remaining concentration of NO2 can be calculated based on the initial stoichiometric ratio.
  • There is a calculation presented that indicates 1.5/2 equals 0.75, which is used to support the claim about the concentration of NO2.

Areas of Agreement / Disagreement

Participants express differing views on the calculations related to the concentrations at 50% completion, indicating a lack of consensus on the interpretation of the stoichiometry and the resulting concentrations.

Contextual Notes

The discussion highlights potential confusion regarding the application of stoichiometric principles in the context of reaction progress and concentration changes, with specific attention to the initial conditions and their impact on the calculations.

Who May Find This Useful

Students and educators in chemistry, particularly those interested in reaction kinetics and stoichiometry in redox reactions.

r_swayze
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Experiments show that the following redox reaction is second-order overall:

NO2(g) + CO(g) --> NO(g) + CO2(g)

In the reaction, the initial [NO2] is twice the initial [CO]. What is the ratio of the initial rate to the rate at 50% completion?

In the solution they say: [NO2]i = 2[CO]i

and then at 50% completion they say: [CO] = 1/2[CO]i and [NO2] = 0.75[NO2]i

where they getting the 1/2 and 0.75 from?
 
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Stoichiometry?

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methods
 
how? can you show the math behind it?

I don't see how they can get .75 if its at 50% completion. Wouldnt that mean NO2 is at 1.5 and CO is at 1? But they can't be since NO2 is twice the initial CO
 
r_swayze said:
the initial [NO2] is twice the initial [CO]

They react 1:1, if half of the CO reacted, how much NO2 was left?

Edit: note, that 1.5/2=0.75...

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