3 Hydrogen and chlorine react to form hydrogen chloride gas, as shown in the equation. \[ \mathrm{H}_{2}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl} \] This equation can be represented as shown. \[ \mathrm{H}-\mathrm{H}+\mathrm{Cl} l \mathrm{Cl} \rightarrow 2 \mathrm{H}-\mathrm{Cl} \] Some bond energies are shown in the table. \begin{tabular}{|c|c|} \hline bond & bond energy in \( \mathrm{kJ} / \mathrm{mol} \) \\ \hline \( \mathrm{H}-\mathrm{H} \) & 436 \\ \hline \( \mathrm{Cl}-\mathrm{Cl} \) & 243 \\ \hline \( \mathrm{H}-\mathrm{Cl} \) & 432 \\ \hline \end{tabular} Calculate the energy change for the reaction between hydrogen and chlorine, using the following steps. - Calculate the energy needed to break the bonds. - Calculate the energy released when bonds are formed. \( \mathrm{kJ} \) \( \mathrm{kJ} \) - Calculate the energy change for the reaction. \( \mathrm{kJ} / \mathrm{mol}[3] \) [Total: 3] 3 4 Carbon is an element in Group IV of the Periodic Table. It reacts with oxygen to form carbon dioxide. The energy level diagram for this reaction is shown. Explain how this diagram shows that the reaction is exothermic. [Tota.
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We need to break one H-H bond and one Cl-Cl bond. The bond energies are given in the table: Energy needed to break H-H bond: 436 kJ/mol Energy needed to break Cl-Cl bond: 243 kJ/mol Total energy needed to break bonds: 436 kJ/mol + 243 kJ/mol = 679 kJ/mol Show more…
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Chloromethane, $\mathrm{CH}_{3} \mathrm{Cl},$ a compound found throughout the environment, is formed in the reaction of chlorine atoms with methane. $$ \mathrm{CH}_{4}(\mathrm{g})+2 \mathrm{Cl}(\mathrm{g}) \rightarrow \mathrm{CH}_{3} \mathrm{Cl}(\mathrm{g})+\mathrm{HCl}(\mathrm{g}) $$ (a) Calculate the enthalpy change for the reaction of $\mathrm{CH}_{4}(\mathrm{g})$ and $\mathrm{Cl}$ atoms to give $\mathrm{CH}_{3} \mathrm{Cl}(\mathrm{g})$ and $\mathrm{HCl}(\mathrm{g}) .$ Is the reaction exo- or endothermic? (b) Draw an energy level diagram that shows how the various enthalpies in this problem are related.
Q $\Delta$ Methane undergoes several different exothermic reactions with gaseous chlorine. One of these forms chloroform, $\mathrm{CHCl}_{3}(\mathrm{~g})$. $$ \begin{aligned} \mathrm{CH}_{4}(\mathrm{~g})+3 \mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow \mathrm{CHCl}_{3}(\mathrm{~g})+3 \mathrm{HCl}(\mathrm{g}) \\ \Delta H_{\mathrm{rxn}}^{0}=-305.2 \mathrm{~kJ} / \mathrm{mol} \mathrm{rxn} \end{aligned} $$ Average bond energies per mole of bonds are: $\mathrm{C}-\mathrm{H}=$ $413 \mathrm{~kJ} ; \mathrm{Cl}-\mathrm{Cl}=242 \mathrm{~kJ} ; \mathrm{H}-\mathrm{Cl}=432 \mathrm{~kJ} .$ Use these to calculate the average $\mathrm{C}-\mathrm{Cl}$ bond energy in chloroform. Compare this with the value in Table $15-2$.
Calculate the amount of energy, in kilojoules, that is involved when 1 mol of nitrogen gas is reacted with 3 mol hydrogen gas to form 2 mol ammonia gas, using the following steps: a. Draw the Lewis structures of all the molecules involved in the reaction: $$ \mathrm{N}_{2}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{NH}_{3}(\mathrm{~g}) $$ b. If the bond energy for the $\mathrm{N} \equiv \mathrm{N}$ bond is $946 \mathrm{~kJ} / \mathrm{mol}$, how much energy is needed to break all the bonds in 1 mol nitrogen molecules? c. If the bond energy for the $\mathrm{H}-\mathrm{H}$ bond is $432 \mathrm{~kJ} / \mathrm{mol}$, how much energy is needed to break all the bonds in 3 mol hydrogen gas? d. If the bond energy for the $\mathrm{N}-\mathrm{H}$ bond is $391 \mathrm{~kJ} / \mathrm{mol}$, how much energy is released when 1 mol ammonia is formed? e. What is the net result of energy needed to break the bonds, less the energy released when new bonds are formed? How do you interpret the sign of that answer?
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