How to find the integrated rate law?

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Discussion Overview

The discussion focuses on finding the integrated rate law for a first-order reaction, exploring various approaches to integration and the correct formulation of the law. It includes attempts at solutions and clarifications regarding integration constants.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant states the rate law as r = -d[A]/dt = k[A] and attempts integration, proposing [A] = (1/2)k*[A]^2, questioning if this is correct.
  • Another participant presents a different integration approach, suggesting that 1/(k*[A]) . d[A] = dt leads to t, and expresses doubt about the first participant's solution.
  • A third participant proposes the equation ln[A] + [A]0 = kt and asks if this is the correct form.
  • A fourth participant suggests ln[A] + C = kt and seeks clarification on why the integration constant is ln[A]0.
  • A fifth participant explains that the integration limits account for the integration constant, indicating that ln(A) corresponds to t and ln[A]0 corresponds to 0.

Areas of Agreement / Disagreement

Participants express differing views on the correct formulation of the integrated rate law, with no consensus reached on the validity of the various proposed solutions.

Contextual Notes

There are unresolved aspects regarding the integration steps and the correct application of limits during integration, which may affect the final form of the integrated rate law.

kasse
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Homework Statement



Find the integrated rate law for a first order reaction


The Attempt at a Solution



We have r = -d[A]/dt = k[A]

Integration with respect to [A] gives

[A] = (1/2)k*[A]^2

Is this it?
 
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d[A]/dt = k[A]

1/(k*[A]) . d[A] = dt

1/(k*[A]) . d[A] = t

now integrate left side ..

I am pretty sure that you have got it wrong
 
ln[A] + [A]0 = kt

Is this the correct form?
 
Last edited:
ln[A] + C = kt

Can anyone explain why the integration constant is ln[A]0?
 
that's due to the integration limits
{from 0 to t}
ln(A) is at t and ln[A]0 is 0
 

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