(2.0) 1. Una muestra de \( { }^{222} \mathrm{Rn} \) contiene inicialmente \( 18,70 \times 10^{-13} \mathrm{~g} \) de este isótopo radiactivo, cuya semivida es de 7,28 días. a. Calcule los núcleos que se han desintegrado después de 12 días. b. Calcule su actividad expresada en becquerel Bq y curios Ci en ese momento. c. El tiempo en segundos que se tarda la muestra radiactiva en reducirse hasta \( 1 / 6 \) de su carga inicial.

3.48 The empirical formula of a compound is CH . If the molar mass of this compound is about 78 g , what is its molecular formula?

Based on bond type, which compound has the highest melting point? 1. \( \mathrm{CH}_{3} \mathrm{OH} \) 2. \( \mathrm{C}_{6} \mathrm{H}_{14} \) 3. \( \mathrm{CaCl}_{2} \) 4. \( \mathrm{CCl}_{4} \)

Questão 1) São dadas as seguintes equações termoquímicas: \( \begin{array}{l}\text { I) } \mathrm{C}_{(\mathrm{s})}+\mathrm{O}_{2(\mathrm{~g})} \longrightarrow \mathrm{CO}_{2(\mathrm{~g})} \quad \Delta \mathrm{H}=-94,1 \mathrm{kcal} / \mathrm{mol} \\ \begin{array}{l}\text { II) } \mathrm{H}_{2(\mathrm{~g})}+1 / 2 \mathrm{O}_{2(\mathrm{~g})}\end{array} \longrightarrow \mathrm{H}_{2} \mathrm{O}_{(\mathrm{l})} \quad \Delta \mathrm{H}=-68,3 \mathrm{kcal} / \mathrm{mol} \\ \text { III) } \mathrm{C}_{(\mathrm{s})}+2 \mathrm{H}_{2(\mathrm{~g})} \longrightarrow \mathrm{CH}_{4(\mathrm{~g})} \quad \Delta \mathrm{H}=-17,9 \mathrm{kcal} / \mathrm{mol} \\ \text { Calcule o calor liberado, em kcal, na reação de combustão de } 1 \text { mol de gás metano. } \\ \mathrm{CH}_{4(\mathrm{~g})}+2 \mathrm{O}_{2(\mathrm{~g})} \longrightarrow \mathrm{CO}_{2(\mathrm{~g})}+2 \mathrm{H}_{2} \mathrm{O}_{(\mathrm{l})} \quad \Delta \mathrm{H}=\text { ? }\end{array} \$ \begin{array}{l}\longrightarrow\end{array} \)

possible Find the hydrogen ion concentration of a solution whose pH is 7.1 . Use the formula \( \mathrm{pH}=-\log \left[\mathrm{H}^{+}\right] \)

Questão 2) Qual o valor da variação de entalpia da reação a seguir? \[ C_{(g r \text { fite })}+\mathrm{O}_{2(g)} \rightarrow \mathrm{CO}_{2(g)} \] Dados: \( \mathrm{C}_{(\mathrm{grffte})}+\frac{1}{2} \mathrm{O}_{2(g)} \rightarrow \mathrm{CO}_{(\mathfrak{g})} \quad \Delta H_{1}=-110,3 \mathrm{KJ} \) \( \mathrm{CO}_{(g)}+\frac{1}{2} \mathrm{O}_{2(g)} \rightarrow \mathrm{CO}_{2(g)} \quad \Delta H_{2}=-283,0 \mathrm{KJ} \)