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# Chemistry rate of reaction urgent!!!

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1. Attachment 547151547153
I don't understand why the rate of reaction is 3.125 which it says on the mark scheme. The rate of reaction is calculated by finding the gradient and I did this for four to eight minutes as can be seen in the first photograph. My working is incorrect as the change in y is 7.5. But 7.5/4 = 1.875 not 3.125. Any help would be appreciated. Thanks in advance.
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2. (Original post by Wolfram Alpha)

Attachment 547151547153
I don't understand why the rate of reaction is 3.125 which it says on the mark scheme. The rate of reaction is calculated by finding the gradient and I did this for four to eight minutes as can be seen in the first photograph. My working is incorrect as the change in y is 7.5. But 7.5/4 = 1.875 not 3.125. Any help would be appreciated. Thanks in advance.
use a tangent bruv, it should tell ya where you got to measure the rate of reaction, is it inital rate of reaction ?
3. (Original post by money-for-all)
use a tangent bruv, it should tell ya where you got to measure the rate of reaction, is it inital rate of reaction ?
The question asks to calculate the rate of reaction from 4-8 minutes. I've never used tangents before in such questions...
4. (Original post by Wolfram Alpha)
The question asks to calculate the rate of reaction from 4-8 minutes. I've never used tangents before in such questions...
well, now is the time to start using them lad.
5. (Original post by money-for-all)
well, now is the time to start using them lad.
No, the question asks for the average, which can get by drawing a line through two points.
6. (Original post by Wolfram Alpha)
The question asks to calculate the rate of reaction from 4-8 minutes. I've never used tangents before in such questions...
You are asked to compare the rate for the first four minutes with the rate from 4-8

There seems to be an error by the teacher. Point it out politely.

Ignore the comment about tangents - your method is correct for average rate.

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