## Chemistry and Chemical Reactivity (9th Edition)

a) For first-order processes: $t_{1/2}=0.693/k\rightarrow k=0.0277\ min^{-1}$ $\ln(C/C_0)=-kt$, at constant volume, we can reduce the concentration ratio to a mass ratio: $\ln(m/8.00\ g)=-0.0277\ min^{-1}\times t$ $m(125\ min)=0.25\ g$ $m(145\ min)=0.14\ g$ b) $\ln(2.25\ ng/7.60\ ng)=-0.0277\ min^{-1}t$ $t=43.9\ min$ c) $\ln(C/C_0)=-kt$ $\ln f=-0.0277\ min^{-1}\times 150\ min$ $f=0.016=1.6\%$