Directions: For the following problems be sure to show the rearranged equations in the space provided below. Cross out any substances which will cancel and demonstrate that the reactions do add up to the overall reaction. Show all calculations related to the ?H's. To the left of the equations, on the line provided, write out what change you are making. 1. Calculate the ?H for the following reaction: (12 pts) 2 P + 5 Cl? ? 2 PCl? Given the following information: __________ PCl? ? PCl? + Cl? ?H = +87.9 kJ __________ P + 3/2 Cl? ? PCl? ?H = -574 kJ
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You wish to know the enthalpy change for the formation of liquid $\mathrm{PCl}_{3}$ from the elements. $$ \mathrm{P}_{4}(\mathrm{s})+6 \mathrm{Cl}_{2}(\mathrm{g}) \rightarrow 4 \mathrm{PCl}_{3}(\ell) \quad \Delta_{r} H^{\circ}=? $$ The enthalpy change for the formation of $\mathrm{PCl}_{5}$ from the elements can be determined experimentally, as can the enthalpy change for the reaction of $\mathrm{PCl}_{3}(\ell)$ with more chlorine to give $\mathrm{PCl}_{5}(\mathrm{s}):$ $\mathrm{P}_{4}(\mathrm{s})+10 \mathrm{Cl}_{2}(\mathrm{g}) \rightarrow 4 \mathrm{PCl}_{5}(\mathrm{s})$ $\Delta_{i} H^{\circ}=-1774.0 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}$ $\mathrm{PCl}_{3}(\ell)+\mathrm{Cl}_{2}(\mathrm{g}) \rightarrow \mathrm{PCl}_{5}(\mathrm{s})$ $$ \Delta_{r} H^{\circ}=-123.8 \mathrm{kJ} / \mathrm{mol}-\mathrm{Dxn} $$ Use these data to calculate the enthalpy change for the formation of 1.00 mol of $\mathrm{PCl}_{3}(\ell)$ from phosphorus and chlorine.
You wish to know the enthalpy change for the formation of liquid $\mathrm{PCl}_{3}$ from the elements. $\mathrm{P}_{4}(\mathrm{~s})+6 \mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow 4 \mathrm{PCl}_{3}(\ell)$ $\Delta H^{\circ}=?$ The enthalpy change for the formation of $\mathrm{PCl}_{5}$ from the elements can be determined experimentally, as can the enthalpy change for the reaction of $\mathrm{PCl}_{3}(\ell)$ with more chlorine to give $\mathrm{PCl}_{5}(\mathrm{~s})$ : $\mathrm{P}_{4}(\mathrm{~s})+10 \mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow 4 \mathrm{PCl}_{5}(\mathrm{~s}) \quad \Delta H^{\circ}=-1774.0 \mathrm{~kJ}$ $\mathrm{PCl}_{3}(\ell)+\mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow \mathrm{PCl}_{5}(\mathrm{~s}) \quad \Delta H^{\circ}=-123.8 \mathrm{~kJ}$ Use these data to calculate the enthalpy change for the formation of $1.00 \mathrm{~mol}$ of $\mathrm{PCl}_{3}(\ell)$ from phosphorus and chlorine.
Write the balanced overall equation (equation 3$)$ for the following process, calculate $\Delta H_{\text { overall }},$ and match the number of each equation with the letter of the appropriate arrow in Figure $\mathrm{P} 6.70$ : (1) $\quad \mathrm{P}_{4}(s)+6 \mathrm{Cl}_{2}(g) \longrightarrow 4 \mathrm{PCl}_{3}(g) \quad \Delta H=-1148 \mathrm{kJ}$ (2) $2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g) \quad \Delta H=-114.2 \mathrm{kJ}$ (3) $\quad\quad\quad\quad\quad \Delta H_{\text { overall }}=?$
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