[himat]

Ok so the question is asking

The first order rate constant, k, for the decomposition of glucose was found to be 6.4 x 10-4 s-1. 
      
How long would it take for

(i)   25% of the glucose to decompose
(ii)    90% of the glucose to decompose

The problem is, there's no initial concentration of glucose given and my immediate thought was to use

t(1/2) = 1/k[A]0

K being the rate constant given and [A]0 being the initial concentration.

As for any other methods im completely clueless and I was wondering how to go about doing this question?

Thanks

[sjb]

Ok so the question is asking

The first order rate constant, k, for the decomposition of glucose was found to be 6.4 x 10-4 s-1. 
      
How long would it take for

(i)   25% of the glucose to decompose
(ii)    90% of the glucose to decompose

The problem is, there's no initial concentration of glucose given and my immediate thought was to use

t(1/2) = 1/k[A]0

K being the rate constant given and [A]0 being the initial concentration.

As for any other methods im completely clueless and I was wondering how to go about doing this question?

Thanks

What is the equation for the half-life of a first order process?

[BluePill]

You don't really need initial concentrations. Just use algebra.

For example:

25% glucose to decompose

ln (A_o/A) = kt

A is the concentration after time t

so, for 25% to decompose, this means that 75% of A_o will be left.

Therefore, A = 0.75 A_o. The A_o term would be cancelled out. The final equation would look like:

ln (1/0.75) = kt

You know k, find t.