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Topic: Working out concentration of reactant given concentration of product and time?  (Read 3263 times)

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Offline bmu123

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I know I'm probably being thick here but for the reaction 2[A] -> [B ], how would I work out the value of [A] given the values of [B ] at given times?
So I'm given
Time/s                          0    10         20       30       ∞
[B ]/moldm-3  0     0.089    0.153   0.200   0.312

So I'm guessing at ∞ [A] = 0 but then I just can't think of what I need to do to work out the rest.
« Last Edit: February 21, 2015, 11:12:43 AM by sjb »

Offline sjb

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I know I'm probably being thick here but for the reaction 2[A] -> [B ], how would I work out the value of [A] given the values of [B ] at given times?
So I'm given
Time/s                          0    10         20       30       ∞
[B ]/moldm-3  0     0.089    0.153   0.200   0.312

So I'm guessing at ∞ [A] = 0 but then I just can't think of what I need to do to work out the rest.

What does the reaction stoichoimetry tell you?

Offline Plontaj

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If the reaction is irreversible, it is quite simple to determine the concentration of A. If it is reversible, will be a little harder.

Offline bmu123

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It is irreversible. So if there are 2 moles of A for every mole of B so double it?

Offline Borek

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Can you use the data given to calculate [ B] at t=∞?
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Offline bmu123

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So if at ∞ [ B] = 0.312, there must have been 0.624 moles of A to begin with?
So could I then say
for 30 seconds [ B] = 0.200; 0.312 - 0.200 = 0.112 and then x 2 so [A] is 0.224?

So
Time    0         10        20       30       ∞
[ B]      0          0.089   0.153   0.200  0.312
[A]      0.624    0.446   0.318   0.224  0
« Last Edit: February 22, 2015, 01:46:41 PM by Borek »

Offline Borek

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I have not checked the numbers, but the logic looks OK to me.
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