Strontium-90 is a radioactive material that decays according to the function \( A(t)=A_{0} e^{-0.0244 t} \), where \( A_{0} \) is the initial amount present and \( A \) is the amount present at time \( t \) (in years). Assume that a scientist has a sample of 800 grams of strontium-90. (a) What is the decay rate of strontium-90? (b) How much strontium- 90 is left after 40 years? (c) When will only 200 grams of strontium-90 be left? (d) What is the half-life of strontium-90? (a) The decay rate of strontium- 90 is \( \square \% \). (Type an integer or a decimal. Include the negative sign for the decay rate.)

1. ¿Cuántos átomos de oxígeno están presentes en \( 0,0500 \mathrm{~mol} \) de \( \mathrm{Ba}(\mathrm{OH})_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O} \) ? \[ \mathrm{N}_{\mathrm{A}}=6,02 \times 10^{23} \] (A. \( 3,01 \times 10^{23} \) B. \( 6,02 \times 10^{23} \) C. \( 3,01 \times 10^{24} \)\( \quad 0.0500 \mathrm{~mol} \mathrm{Ba}(\mathrm{OH})_{2} \).

If the half-life of I-131 is 10.4 days, how many moles of I-131 would be left in Mr. Miller's body after 47 days if he was infused with 7.2 grams? (Round your answer to four decimal places) 0.0117

Las reacciones de doble desplazamiento, son aquellas en las cuales dos elementos de un compuesto, son sustituidos por otros dos elementos al pasar a productos. De las reacciones dadas a continuación, zcuáles de doble desplazamiento? A. \( 2 \mathrm{KI}+\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2} \rightarrow \mathrm{PbI}+2 \mathrm{KNO}_{3} \) B. \( \mathrm{Bi}_{2}\left(\mathrm{SO}_{4}\right)_{3} \rightarrow \mathrm{Bi}_{2} \mathrm{~S}_{3}+6 \mathrm{O}_{2} \) C \( 2 \mathrm{BI}_{2}+6 \mathrm{HCl} \rightarrow 2 \mathrm{BiCl}_{3}+3 \mathrm{H}_{2} \) D. \( \mathrm{N}_{2}+3 \mathrm{H}_{2} \rightarrow 2 \mathrm{NH}_{3} \)

2. Find \( \Delta \mathrm{H}^{\circ} \) for the reaction \( 2 \mathrm{H}_{2}(\mathrm{~g})+2 \mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\mathrm{l}) \), using the following thermochemical data. \( \begin{array}{ll}\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\mathrm{l})+2 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) & \Delta \mathrm{H}=-875 \mathrm{~kJ} \\ \mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{CO}_{2}(\mathrm{~g}) & \Delta \mathrm{H}=-394.51 \mathrm{~kJ} \\ \mathrm{H}_{2}(\mathrm{~g})+1 / 2 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) & \Delta \mathrm{H}=-285.8 \mathrm{~kJ}\end{array} \)

If the half-life of I-131 is 10.4 days, how many moles of I-131 would be left in Mr. Miller's body after 47 days if he was infused with 7.2 grams? (Round your answer to four decimal places)