1) How does the initial reactant concentration affect: the initial reaction rate
ID: 943612 • Letter: 1
Question
1) How does the initial reactant concentration affect:
the initial reaction rate?
the overall reaction order?
the rate constant?
2) How does the temperature affect:
the initial reaction rate?
the overall reaction order?
the rate constant?
3) How can the instantaneous rate of reaction be determined from the graphs?
4) How can the reaction order for a specific chemical species be determined from the graphs?
5) How can the rate constant be determined from the graphs?
6) Under what conditions does the rate constant remain constant?
Graphs: http://imgur.com/a/bOJpg
Effect of Temperature on Rate of Chloromethane Solvolysis 5 Effect of [CH3Cl]i on Rate of Chloromethane Solvolysis 9 1.20E-02 1.00E-02 8.00E-0 1.00E-01 9.00E-02 8.00E-02 7.00E-02 6.00E-02 5.00E-02 4.00E-02 3.00E-02 2.00E-02 1.00E-02 0.00E+00 0 03 M 04 M .05 M 6.00E-03 75'C .79 85 90 400E-03 2.00E-03 .08 M 0.00E+00 100 200 300 1000 2000 3000 4000 5000 6000 Time (min) Time (min) Ln [CH3Ci] vs. Time for Changing Temperatures Ln[CH3Ci] vs. Time for Changing [CH3CIl 1000 2000 3000 4000 70 03M 04M .79 85 4.5 06M 95 Time (min) Time (min) /[CH3cj vs. Time for Changing Temperatures /CH,cj vs. Time for Changing [CH3CIl 03M 04M ·75 79 85 06M 100 09M 150 200 250 300 350 Time (min) 1000 4000 5000 6000 50 100 Time (min)Explanation / Answer
1) Effect of initial concentration
As the initial concentration of [CH3Cl] goes up, the rate of reaction decreases.
The overall order of reaction stayed as first order.
The rate constant was also seen to increase with increasing initial concentration of [CH3Cl]
2) Effect of temperature
As the reaction temperature increases, the initial reaction rate goes down.
With increasing reaction temperature the overall reaction order stayed as first order kinetics.
The rate constant and temperature are found to have an indirect relationship, thus as temperature increase, rate constant was found to decrease.
3) Instantaneous rate determination
Is the slope of line from graph ln[CH3Cl] vs time
slope = -k = -d[lnCH3Cl]/dt
So k is the instantaneous rate of the reaction.
So from the graph of ln[CH3Cl] vs time, slope is equal to instantaneous rate of that particular reaction.
4) A plot of [CH3Cl] vs time for a zero order reaction, ln[CH3Cl] vs time for a first order reaction and 1/[CH3Cl] vs time for a second order is drawn. The graph which gives us a straight line is the order of the reaction.
As can ben seen a graph of ln[CH3Cl] vs time gives us a straight line plot, which tells that the reaction follows a first order kinetics.
5) Rate constant k = -slope
So rate constant k can be determined by taking the slope of line and then taking -ve of that.
slope = -k
so k = slope
6) Under first order reaction condition the rate constant remains constant.
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