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November 01, 2025, 12:50:51 pm
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Author Topic: Neap 2009 Exam question  (Read 993 times)  Share 

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arthurk

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Neap 2009 Exam question
« on: October 17, 2009, 01:51:35 pm »
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For question 3d it asked if we used the same ph of solutions of HCL and another weak acid would we have the same reaction rate
the answer states that 'Both solutions have the same concentration of H+(aq), the reacting species, and so would
have the same reaction rate.'
My teacher came up with the idea that because weak acids are only partially ionised the H+ could be somewhat renewed as it is being used in the process due to a shift in equilibrium to the right as H+ is used while HCL has a define H+ concentration since it is completely ionised from the beginning thus H+ will be consumed only
Should that not mean that the weak acid has a faster reaction rate as H+ is being used but somewhat renewed in the process, even to a slight extent compared to that of HCl?
Views on this?
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thisongaintgottaname

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Re: Neap 2009 Exam question
« Reply #1 on: October 17, 2009, 09:03:06 pm »
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maybe the question is just concerning about the initial reaction rate which purely depends on the concentration of H+ present, as the rate may vary over time due to changes in conditions? :)
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Dark Horse

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Re: Neap 2009 Exam question
« Reply #2 on: October 17, 2009, 09:36:58 pm »
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yeah lol, i thought the same thing! I reckon I would have said they had the same rate, but that question on last years unit 4 exam made me overthink it and say the weak acid has the faster rate. But realistically, my teacher said that the equilibrium shift will not really affect the rate of reaction. Im still not sure though, so I wonder if anyone is sure about the answer to this? 
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arthurk

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Re: Neap 2009 Exam question
« Reply #3 on: October 17, 2009, 09:57:01 pm »
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Quote from: thisongaintgottaname on October 17, 2009, 09:03:06 pm
maybe the question is just concerning about the initial reaction rate which purely depends on the concentration of H+ present, as the rate may vary over time due to changes in conditions? :)
The question simply states rate of reaction and not initial rate

Quote from: Dark Horse on October 17, 2009, 09:36:58 pm
yeah lol, i thought the same thing! I reckon I would have said they had the same rate, but that question on last years unit 4 exam made me overthink it and say the weak acid has the faster rate. But realistically, my teacher said that the equilibrium shift will not really affect the rate of reaction. Im still not sure though, so I wonder if anyone is sure about the answer to this? 

equilibrium shift not really affect it? hmm? this sort of thing usually comes up on vcaa exams to take a few marks away from those that dont overthink things.
But if it has been experimentally proven to be negligible then im happy with that

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