6. During a chemical reaction, energy is either released or absorbed 7. Is the following sentence true or false? Physical and chemical changes can be either exothermic or endothermic changes. 8. What is an exothermic reaction? 9. Is the following sentence true or false? In exothermic reactions, the energy required to break the bonds in the reactants is greater than the energy released as the products form.

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

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. \( \mathrm{CCl}_{4} \)

14 Nitrogen has atomic number 7 and oxygen has atomic number 8 What is total number of electrons in \( \left(\mathrm{NO}_{3}\right)^{-} \)ion ? \( \begin{array}{ll}\text { (a) } 15 \mathrm{e}^{-} & \text {(b) } 31 \mathrm{e}^{-} \\ \text {(c) } 32 \mathrm{e}^{-} & \text {(d) } 46 \mathrm{e}^{-}\end{array} \)

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?

10 Essay 5 points Please identify the following components for the element Selenium: 1 Chemical Symbol 2. Atomic Number 3. Family \# 4. Valence Electrons 5. Category Edit View Insert Format Tools Table