[gt5hz]

"Sucrose reacts with water to form glucose and fructose."

C12H2O11 + H2O ---> C6H12O6 + C6H12O6

At temperature T1, the reaction has the rate law k[C12H22O11] with k=6.17 x 10^-4 s^-1.

I calculated the half life of the rxn in seconds, and got 1.12 x 10^3s.

The question I have trouble on is this...

How long, in minutes, does it take for three quarters of sucrose to react when T=T1.

Here's what I've tried:

Setting up a relation below...
3/4 [C12H22O11] = (1/2)^n [C12H22O11] and solving for n, which equals roughly .41. Then I multiply it by 1.12 x 10^3s to get 7.7 mins. To be honest, I've no idea why I'm doing this; there was an example in the text that was along these lines.

The real answer is 37.3mins. Through inspection, that is equal to twice the half life of the reaction in seconds.

How was this amount attained? Thanks in advance.

[sjb]

What does the half-life of the reaction mean in terms of concentration of starting material? If you had X amount at the start, how much would you have after one half-life?

[gt5hz]

What does the half-life of the reaction mean in terms of concentration of starting material? If you had X amount at the start, how much would you have after one half-life?

Half of X.

[DrCMS]

So how much left after 2 half life's?  So how much has reacted?

Now read the question and look at what you to attempted to calculate.

[gt5hz]

So how much left after 2 half life's?  So how much has reacted?

Now read the question and look at what you to attempted to calculate.

Oh jeez. Doy!

Thank you for your help sjb and DrCMS.