For each of the following compounds, write a balanced thermochemical equation depicting the formation of one mole of the compound from its elements in their standard states and then look up \(\Delta H^{\circ}{ }_{f}\) for each substance in Appendix \(\mathrm{C}\). (a) \(\mathrm{NO}_{2}(g),\) (b) \(\mathrm{SO}_{3}(g),\) (c) \(\mathrm{NaBr}(s),\) (d) \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(s).\)

Short Answer

Expert verified
(a) \(\frac{1}{2}N_{2}(g) + O_{2}(g) \rightarrow NO_{2}(g)\), \(\Delta H^{\circ}{ }_{f} = +33.2\,\mathrm{kJ\,mol^{-1}}\) (b) \(S(s) + \frac{3}{2}O_{2}(g) \rightarrow SO_{3}(g)\), \(\Delta H^{\circ}{ }_{f} = -395.7\,\mathrm{kJ\,mol^{-1}}\) (c) \(Na(s) + \frac{1}{2}Br_{2}(l) \rightarrow NaBr(s)\), \(\Delta H^{\circ}{ }_{f} = -362.7\,\mathrm{kJ\,mol^{-1}}\) (d) \(Pb(s) + N_{2}(g) + 3\,O_{2}(g)\rightarrow Pb(NO_{3})_{2}(s)\), \(\Delta H^{\circ}{ }_{f} = -765.6\,\mathrm{kJ\,mol^{-1}}\)

Step by step solution

01

(a) Formation of NO2(g)

: From its elements, Nitrogen and Oxygen, we can write the balanced thermochemical equation for the formation of one mole of \(\mathrm{NO}_{2}(g)\) as: \[ \frac{1}{2}N_{2}(g) + O_{2}(g) \rightarrow NO_{2}(g) \] To find the \(\Delta H^{\circ}{ }_{f}\) for one mole of \(\mathrm{NO}_{2}(g)\), refer to Appendix \(\mathrm{C}\) and look for the value. You should find that the \(\Delta H^{\circ}{ }_{f}\) for \(\mathrm{NO}_{2}(g)\) is \( +33.2\,\mathrm{kJ\,mol^{-1}} \).
02

(b) Formation of SO3(g)

: From its elements, Sulfur and Oxygen, we can write the balanced thermochemical equation for the formation of one mole of \(\mathrm{SO}_{3}(g)\) as: \[ S(s) + \frac{3}{2}O_{2}(g) \rightarrow SO_{3}(g) \] To find the \(\Delta H^{\circ}{ }_{f}\) for one mole of \(\mathrm{SO}_{3}(g)\), refer to Appendix \(\mathrm{C}\) and look for the value. You should find that the \(\Delta H^{\circ}{ }_{f}\) for \(\mathrm{SO}_{3}(g)\) is \( -395.7\,\mathrm{kJ\,mol^{-1}} \).
03

(c) Formation of NaBr(s)

: From its elements, Sodium and Bromine, we can write the balanced thermochemical equation for the formation of one mole of \(\mathrm{NaBr}(s)\) as: \[ Na(s) + \frac{1}{2}Br_{2}(l) \rightarrow NaBr(s) \] To find the \(\Delta H^{\circ}{ }_{f}\) for one mole of \(\mathrm{NaBr}(s)\), refer to Appendix \(\mathrm{C}\) and look for the value. You should find that the \(\Delta H^{\circ}{ }_{f}\) for \(\mathrm{NaBr}(s)\) is \( -362.7\,\mathrm{kJ\,mol^{-1}} \).
04

(d) Formation of Pb(NO3)2(s)

: From its elements, Lead, Nitrogen, and Oxygen, we can write the balanced thermochemical equation for the formation of one mole of \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(s)\) as: \[ Pb(s) + 2\,NO_{3}^{-}(aq) \rightarrow Pb(NO_{3})_{2}(s) \] Please note that nitrate ions \(\mathrm{NO}_{3}^{-}\) are formed from Nitrogen and Oxygen: \[ 2\,N(g) + 6\,O_{2}(g) \rightarrow 4\,NO_{3}^{-}(aq) \] Thus, for the balanced thermochemical equation for \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(s)\), we have: \[ Pb(s) + N_{2}(g) + 3\,O_{2}(g)\rightarrow Pb(NO_{3})_{2}(s) \] To find the \(\Delta H^{\circ}{ }_{f}\) for one mole of \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(s)\), refer to Appendix \(\mathrm{C}\) and look for the value. You should find that the \(\Delta H^{\circ}{ }_{f}\) for \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(s)\) is \( -765.6\,\mathrm{kJ\,mol^{-1}} \).

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Most popular questions from this chapter

Ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) is blended with gasoline as an automobile fuel. (a) Write a balanced equation for the combustion of liquid ethanol in air. (b) Calculate the standard enthalpy change for the reaction, assuming \(\mathrm{H}_{2} \mathrm{O}(g)\) as a product. (c) Calculate the heat produced per liter of ethanol by combustion of ethanol under constant pressure. Ethanol has a density of $0.789 \mathrm{~g} / \mathrm{mL}$. (d) Calculate the mass of \(\mathrm{CO}_{2}\) produced per kJ of heat emitted.

A sample of a hydrocarbon is combusted completely in \(\mathrm{O}_{2}(g)\) to produce $21.83 \mathrm{~g} \mathrm{CO}_{2}(g), 4.47 \mathrm{~g} \mathrm{H}_{2} \mathrm{O}(g),\( and \)311 \mathrm{~kJ}$ of heat. (a) What is the mass of the hydrocarbon sample that was combusted? (b) What is the empirical formula of the hydrocarbon? (c) Calculate the value of \(\Delta H_{f}^{\circ}\) per empiricalformula unit of the hydrocarbon. (d) Do you think that the hydrocarbon is one of those listed in Appendix C? Explain your answer.

Calcium carbide \(\left(\mathrm{CaC}_{2}\right)\) reacts with water to form acetylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)\) and \(\mathrm{Ca}(\mathrm{OH})_{2}\). From the following enthalpy of reaction data and data in Appendix C, calculate \(\Delta H_{f}^{\circ}\) for \(\mathrm{CaC}_{2}(s);\) $$ \begin{aligned} \mathrm{CaC}_{2}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s)+\mathrm{C}_{2} \mathrm{H}_{2}(g) & \\ \Delta H^{\circ}=&-127.2 \mathrm{~kJ} \end{aligned} $$

(a) Derive an equation to convert the specific heat of a pure substance to its molar heat capacity. (b) The specific heat of aluminum is $0.9 \mathrm{~J} /(\mathrm{g} \cdot \mathrm{K}) .$ Calculate its molar heat capacity. (c) If you know the specific heat of aluminum, what additional information do you need to calculate the heat capacity of a particular piece of an aluminum component?

The heat of combustion of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l),\( is -1367 \)\mathrm{kJ} / \mathrm{mol}$. A bottle of stout (dark beer) contains up to \(6.0 \%\) ethanol by mass. Assuming the density of the beer to be \(1.0 \mathrm{~g} / \mathrm{mL},\) what is the caloric content due to the alcohol (ethanol) in a bottle of beer \((500 \mathrm{~mL})\) ?

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