Chemical thermodynamics

Bond energy

Exercise 4

  

Use the →   Table of enthalpies of formation to calculate the standard enthalpy of the reaction $NH_3(g)$ $+$ $3F_2(g)$ $\longrightarrow$ $NF_3(g)$ $+$ $3HF(g)$ Find the bond energy of the $N-F$ bond using the →   Table of bond energies

$NH_3(g)$ $+$ $3F_2(g)$ $\longrightarrow$ $NF_3(g)$ $+$ $3HF(g)$ $\Delta H$ $ = $ $\Delta H_f(NF_3(g))$ $ +$ $ 3\Delta H_f(HF(g))$ $ - $ $\Delta H_f(NH_3(g))$ $=$ $ -880.19\;kJ$

$\Delta H$ $=$ $3E_{bond}(N-H)$ $ +$ $ 6E_{bond}(F-F)$ $ - $ $(3E_{bond}(N-F)$ $+$ $3E_{bond}(H-F)$ Let be $x$ $=$ $E_{bond}(N-F)$: $-880.19$ $ =$ $ 3\cdot 389$ $ +$ $6\cdot 155$ $-$ $3x$ $-$ $3\cdot 565$ $E_{bond}(N-F)$ $=$ $x$ $=$ $427\; kJ$