[bmu123]

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.

[sjb]

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?

[Plontaj]

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

[bmu123]

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

[Borek]

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

[bmu123]

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

[Borek]

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