# How to find initial rate of reaction from absorbance vs time graph ?

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#1
Hello,

I have a absorbance vs time graph and I need to find initial rate of reaction and also answer needs to come back as a ......△A340min-1. I am going to put links of graph and information about graph here. I really appreciate if someone help me because its been a week and I don't understand a thing. Thank you again.

Graph:
https://ibb.co/w0Fw19v

https://ibb.co/RPbb4h2
0
2 years ago
#2
(Original post by Elenngilbrt)
Hello,

I have a absorbance vs time graph and I need to find initial rate of reaction and also answer needs to come back as a ......△A340min-1. I am going to put links of graph and information about graph here. I really appreciate if someone help me because its been a week and I don't understand a thing. Thank you again.

Graph:
https://ibb.co/w0Fw19v

https://ibb.co/RPbb4h2
The graph should be a curve, so draw a tangent at time zero and find its gradient

Graph is a curve because rate of reaction decreases as time proceeds since concentration of reactants decrease
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#3
(Original post by BobbJo)
The graph should be a curve, so draw a tangent at time zero and find its gradient

Graph is a curve because rate of reaction decreases as time proceeds since concentration of reactants decrease
How I do that can you show me please I dont understand how to do it. I never done this type of question before.
0
2 years ago
#4
(Original post by Elenngilbrt)
How I do that can you show me please I dont understand how to do it. I never done this type of question before.
You need to draw a curve not a straight line. Then draw a tangent to the curve at time zero and find its gradient
1
#5
(Original post by BobbJo)
You need to draw a curve not a straight line. Then draw a tangent to the curve at time zero and find its gradient
My teacher told me to do linear (line of best fit) for each results.
0
2 years ago
#6
(Original post by Elenngilbrt)
My teacher told me to do linear (line of best fit) for each results.
then the rate of reaction is constant and equal to the gradient
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#7
(Original post by BobbJo)
then the rate of reaction is constant and equal to the gradient
Okay but it says what is initial rate of reaction of pH 7 and pH 8.5 how do I find it ? and there is a space for answer it ends with △A340min-1. I am just so confused.
0
2 years ago
#8
(Original post by Elenngilbrt)
Okay but it says what is initial rate of reaction of pH 7 and pH 8.5 how do I find it ? and there is a space for answer it ends with △A340min-1. I am just so confused.
The rate of reaction at pH 7 is the gradient of the line you got for experiment at pH 7
The rate of reaction at pH 8.5 is the gradient of the line you got for experiment at pH 8.5

Units of gradient is units on vertical axis/units on horizontal axis = (340nm)/min = 340nm min^-1 which is what they mean by △A340min-1
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#9
(Original post by BobbJo)
The rate of reaction at pH 7 is the gradient of the line you got for experiment at pH 7
The rate of reaction at pH 8.5 is the gradient of the line you got for experiment at pH 8.5

Units of gradient is units on vertical axis/units on horizontal axis = (340nm)/min = 340nm min^-1 which is what they mean by △A340min-1
Okay so, what i need to do is to divide absorbance/ time to find pH 7's initial rate and pH 8.5 ?
0
2 years ago
#10
(Original post by Elenngilbrt)
Okay so, what i need to do is to divide absorbance/ time to find pH 7's initial rate and pH 8.5 ?
0
#11
(Original post by BobbJo)
Okay thank you BobbJo.
0
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