Kinetics Question: Rate of Reaction at 0.503 M

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Discussion Overview

The discussion revolves around a kinetics problem involving the reaction 2 A + 2 B → C + D at a temperature of 282 K. Participants are tasked with determining the rate of reaction when the concentrations of A and B are both 0.503 M, given initial concentrations and a slope from a plot of ln[A] vs time.

Discussion Character

  • Homework-related, Exploratory, Technical explanation

Main Points Raised

  • One participant presents the reaction and the initial conditions, stating the rate equation and the slope from the ln[A] plot.
  • Another participant questions the significance of the change in concentration of [B] relative to its initial value during the experiment.
  • There is a suggestion that an ICE table may be necessary to solve the problem, although some participants express uncertainty about its relevance.
  • Further clarification is provided on what an ICE table entails, focusing on initial concentrations, changes, and final concentrations.
  • One participant prompts a reconsideration of the final concentration of B if all A had reacted, asking about the percentage change in concentration.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the necessity of using an ICE table, and there is ongoing exploration of the implications of concentration changes during the reaction.

Contextual Notes

There are unresolved assumptions regarding the significance of concentration changes and the application of the rate law in this context. The discussion does not clarify the mathematical steps needed to arrive at the rate of reaction.

Who May Find This Useful

Students studying chemical kinetics, particularly those working on homework problems related to reaction rates and concentration changes.

davev
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Homework Statement


Consider the following reaction at 282 K.

2 A + 2 B → C + D​

where rate = rate=k[A]2. An experiment was performed for a certain number of seconds where [A]0 = 0.000303 M and 0 = 1.63 M. A plot of ln[A] vs time had a slope of -7.27. What will the rate of this reaction be when [A] = = 0.503 M?

Rate (M/s)=

The correct answer is 0.348 M/s.

Homework Equations


I'm not sure where to start here, but I tried using these equations, because I was given the slope, and the slope for ln[A] vs time is given in a first order reaction:

ln[A]t = -kt + ln[A]o
Rate = k[A]
k = -slope


The Attempt at a Solution


Basically I just tried plugging into k = 7.27 into rate=k[A]2 were [A] and are both 0.503 M.

Thank you for the help!
 
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Look at the values of [A] and at the beginning of the experiment. From the specified stoichiometry, how much do you think the concentration of is going to change relative to its initial value during the experiment? Will this really be significant?

Chet
 
Oh, do I have to use an ICE table?
 
davev said:
Oh, do I have to use an ICE table?
I don't know what an ICE table is, but, whatever it is, you don't need to use it on this problem.

Chet
 
Chestermiller said:
I don't know what an ICE table is, but, whatever it is, you don't need to use it on this problem.

Chet

ICE as in initial concentration, change in concentration, and end concentration.

How do you solve this problem?
 
davev said:
ICE as in initial concentration, change in concentration, and end concentration.

How do you solve this problem?
The solution to this problem starts out by reconsidering the questions I asked in post #2. Let me ask in another way. If B had reacted with all the A in the experiment, what would its final concentration have been? What percentage change would this have made in the concentration of B?

Chet
 

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