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Chapter 8: Problem 69

Use bond energy values (Table 8.5\()\) to estimate \(\Delta H\) for each of the following reactions in the gas phase. a. \(\mathrm{H}_{2}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl}\) b. $\mathrm{N} \equiv \mathrm{N}+3 \mathrm{H}_{2} \rightarrow 2 \mathrm{NH}_{3}$

Short Answer

Expert verified
Using bond energy values and the formula \(\Delta H = \text{Energy of bonds broken} - \text{Energy of bonds formed}\), we calculated the change in enthalpy (\(\Delta H\)) for two reactions: a. \(\mathrm{H}_{2}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl}\) \(\Delta H = -190\text{ kJ/mol}\) b. $\mathrm{N} \equiv \mathrm{N}+3 \mathrm{H}_{2} \rightarrow 2 \mathrm{NH}_{3}$ \(\Delta H = -93\text{ kJ/mol}\)

Step by step solution

01

Reaction a: H2 + Cl2 -> 2 HCl

In this reaction, one H-H bond and one Cl-Cl bond are broken, and two H-Cl bonds are formed. Look up the bond energy values for these bonds in Table 8.5: H-H bond: 432 kJ/mol Cl-Cl bond: 242 kJ/mol H-Cl bond: 432 kJ/mol
02

Reaction b: N≡N + 3 H2 -> 2 NH3

In this reaction, one N≡N triple bond and three H-H bonds are broken, and six N-H bonds are formed. Look up the bond energy values for these bonds in Table 8.5: N≡N triple bond: 941 kJ/mol H-H bond: 432 kJ/mol N-H bond: 391 kJ/mol **Step 2: Calculate \(\Delta H\) for each reaction** For each reaction, calculate \(\Delta H\) using the following formula: \(\Delta H = \text{Energy of bonds broken} - \text{Energy of bonds formed}\)
03

Reaction a: Calculate \(\Delta H\)

Calculate \(\Delta H\) for reaction a using the bond energies from Step 1: \(\Delta H = (1\cdot432 + 1\cdot242) - 2\cdot432 = -190\text{ kJ/mol}\)
04

Reaction b: Calculate \(\Delta H\)

Calculate \(\Delta H\) for reaction b using the bond energies from Step 1: \(\Delta H = (1\cdot941 + 3\cdot432) - 6\cdot391 = -93\text{ kJ/mol}\) Now, we have the change in enthalpy (\(\Delta H\)) for both reactions: a. \(\mathrm{H}_{2}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl}\) \(\Delta H = -190\text{ kJ/mol}\) b. $\mathrm{N} \equiv \mathrm{N}+3 \mathrm{H}_{2} \rightarrow 2 \mathrm{NH}_{3}$ \(\Delta H = -93\text{ kJ/mol}\)

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Most popular questions from this chapter

Which of the following incorrectly shows the bond polarity? Show the correct bond polarity for those that are incorrect. a. \(^{\delta+} \mathrm{H}-\mathrm{F}^{\delta-} \quad\) d. $\delta^{+} \mathrm{Br}-\mathrm{Br}^{\delta-}$ b. \(^{\delta+} \mathrm{Cl}-\mathrm{I}^{\delta-} \qquad\) e. \(\quad\) e. $\quad ^{\delta+}\mathrm{O}-\mathrm{P}^{\delta-}$ c. \(\quad \delta+\mathrm{Si}-\mathrm{S}^{\delta-}\)

Think of forming an ionic compound as three steps (this is a simplification, as with all models): (1) removing an electron from the metal; (2) adding an electron to the nonmetal; and (3) allowing the metal cation and nonmetal anion to come together. a. What is the sign of the energy change for each of these three processes? b. In general, what is the sign of the sum of the first two processes? Use examples to support your answer. c. What must be the sign of the sum of the three processes? d. Given your answer to part c, why do ionic bonds occur? e. Given your above explanations, why is NaCl stable but not $\mathrm{Na}_{2} \mathrm{Cl} ? \mathrm{NaCl}_{2} ?$ What about MgO compared to \(\mathrm{MgO}_{2} ? \mathrm{Mg}_{2} \mathrm{O} ?\)

Although both \(\mathrm{Br}_{3}^{-}\) and \(\mathrm{I}_{3}^{-}\) ions are known, the \(\mathrm{F}_{3}-\) ion has not been observed. Explain.

Use bond energies to estimate \(\Delta H\) for the combustion of one mole of acetylene: $$\mathrm{C}_{2} \mathrm{H}_{2}(g)+\frac{5}{2} \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)$$

Write Lewis structures that obey the octet rule (duet rule for H) for each of the following molecules. a. \(\mathrm{H}_{2} \mathrm{CO} \quad\) c. \(\mathrm{HCN}\) b. \(\mathrm{CO}_{2}\)
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