[yazz]

the half life of a certain first order reaction is 120s.how long do you estimate that it will take for 90% of the original sample to react?
halflife=120s
k=?
.693
k=5.7*10to power -3
120s=1/k(5.7*10-3)
this is what i have ,somebody please help

[berb]

Hi, I worked out this problem on paper and scanned it because I'm very bad at expressing math using a keyboard 



Hopefully you're able to follow my work, the first A is the remaining percentage after reaction (10% or .1, since 90% of the original sample reacted) and the Asub0 is the original amount started with (100% or 1).