b) Consider following two paths for the preparation of methylene chloride. Path I : [ mathrm{CH}_{4}(mathrm{~g})+2 mathrm{Cl}_{2}(mathrm{~g}) ightarrow mathrm{CH}_{2} mathrm{Cl}_{2}(mathrm{~g})+2 mathrm{HCl}(mathrm{g}) quad Delta mathrm{H}_{1}=-202.3 mathrm{~kJ} ] Path II : [ egin{array}{ll} mathrm{CH}_{4}(mathrm{~g})+mathrm{Cl}_{2}(mathrm{~g}) ightarrow mathrm{CH}_{3} mathrm{Cl}(mathrm{g})+mathrm{HCl}(mathrm{g}) & Delta mathrm{H}_{2}=-98.3 mathrm{~kJ} \ mathrm{CH}_{3} mathrm{Cl}(mathrm{g})+mathrm{Cl}_{2}(mathrm{~g}) ightarrow mathrm{CH}_{2} mathrm{Cl}_{2}(mathrm{~g})+mathrm{HCl}(mathrm{g}) & Delta mathrm{H}_{3}=-104.0 mathrm{~kJ} end{array} ] Based on the reaction scheme above, explain how to determine the heat of a chemical reaction. (4 marks)
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It is a state function, meaning it only depends on the initial and final states of the system, not on the path taken to get there. In the given question, we have two paths to prepare methylene chloride and we are given the enthalpy changes for each step in both Show more…
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The industrial degreasing solvent methylene chloride, CH2Cl2, is prepared from methane by reaction with chlorine: $$ \mathrm{CH}_{4}(g)+2 \mathrm{Cl}_{2}(g) \longrightarrow \mathrm{CH}_{2} \mathrm{Cl}_{2}(g)+2 \mathrm{HCl}(g) $$ Use the following data to calculate $\Delta H^{\circ}$ in kilojoules for the reaction: $$ \begin{array}{ll}{\mathrm{CH}_{4}(g)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{Cl}(g)+\mathrm{HCl}(g)} & {\Delta H^{\circ}=-98.3 \mathrm{kJ}} \\ {\mathrm{CH}_{3} \mathrm{Cl}(g)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{CH}_{2} \mathrm{Cl}_{2}(g)+\mathrm{HCl}(g)} & {\Delta H^{\circ}=-104 \mathrm{kJ}}\end{array} $$
Calculate $\Delta H_{\mathrm{rsn}}$ for the reaction: $$ \mathrm{CH}_{4}(\mathrm{~g})+4 \mathrm{Cl}_{2}(g) \longrightarrow \mathrm{CCl}_{4}(g)+4 \mathrm{HCl}(g) $$ Use the following reactions and given $\Delta H$ 's. $$ \begin{array}{cc} \mathrm{C}(s)+2 \mathrm{H}_{2}(g) \longrightarrow \mathrm{CH}_{4}(g) & \Delta H=-74.6 \mathrm{~kJ} \\ \mathrm{C}(s)+2 \mathrm{Cl}_{2}(g) \longrightarrow \mathrm{CCl}_{4}(g) & \Delta H=-95.7 \mathrm{~kJ} \\ \mathrm{H}_{2}(g)+\mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{HCl}(g) & \Delta H=-92.3 \mathrm{~kJ} \end{array} $$
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.
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