# Kinetics question on rate of reaction......

#1
Shouldn't the graph of a concentration-time graph have a negative gradient curve? as opposed to an increasing gradient curve? I'll send an attachment below, and my working along with it..
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#2
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#3
this is what the mark scheme for this question shows.. although it doesn't make any sense at all.. shouldn't the concentration of the acid decrease with time?? which is as reaction rate decreases?? I would understand the shape of the graph if it were one for the volume of gas evolved.. but its not.. please help.
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4 months ago
#4
(Original post by Abraham_Otaku)
this is what the mark scheme for this question shows.. although it doesn't make any sense at all.. shouldn't the concentration of the acid decrease with time?? which is as reaction rate decreases?? I would understand the shape of the graph if it were one for the volume of gas evolved.. but its not.. please help.
Would have been better to put this in Chemistry rather than maths - I've requested admin to move it.

That said, I'd take the concentration in the graph to be that of .

Since there is an excess of HCl, then it's concentration can't start at zero, so graph is clearly incorrrect.
Last edited by ghostwalker; 4 months ago
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#5
oh.. I wasn't aware that it was in the maths forum...

(Original post by ghostwalker)
Would have been better to put this in Chemistry rather than maths - I've requested admin to move it.

That said, I'd take the concentration in the graph to be that of .

Since there is an excess of HCl, then it's concentration can't start at zero, so graph is clearly incorrrect.
So does that mean that the graph given in the mark scheme is wrong, and mine is correct?(sorry if this is a stupid and obvious question)
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4 months ago
#6
(Original post by Abraham_Otaku)
oh.. I wasn't aware that it was in the maths forum...

So does that mean that the graph given in the mark scheme is wrong, and mine is correct?(sorry if this is a stupid and obvious question)
Sorry, I wasn't clear.

Concentration of HCl decreases from the start at a decreasing rate over time, down to a constant, non-zero, value since there is an excess of HCl.
Also the curve for the powder will be below that of the chips, since the powder will react faster; until they come together at the constant final value.

Edit: Assuming equal weights of chips and powder and the same concentration of HCl at the start.
Last edited by ghostwalker; 4 months ago
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#7
thank you!

(Original post by ghostwalker)
Sorry, I wasn't clear.

Concentration of HCl decreases from the start at a decreasing rate over time, down to a constant, non-zero, value since there is an excess of HCl.
Also the curve for the powder will be below that of the chips, since the powder will react faster; until they come together at the constant final value.

Edit: Assuming equal weights of chips and powder and the same concentration of HCl at the start.
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