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

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..
7f2a23d4-7be2-4294-88a0-5d95b93dd1c1.jpeg
Screenshot 2022-01-19 112717.png52.5KB
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.
Screenshot 2022-01-19 113452.png47.7KB
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 CaCl2CaCl_2.

Since there is an excess of HCl, then it's concentration can't start at zero, so graph is clearly incorrrect.
(edited 2 years ago)
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 CaCl2CaCl_2.

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)
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.

Yes, your graph looks correct.

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.
(edited 2 years ago)
thank you!:biggrin:

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

Yes, your graph looks correct.

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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