What is the standard $N \equiv N$ bond enthalpy from the following reaction? $N_{2(g)} + 3H_{2(g)} \longrightarrow 2NH_{3(g)} \quad \Delta H^{\circ} = -83 \ kJ$
Given: $(\Delta H^{\circ}_{(H-H)} = 435 \ kJ \text{ mol}^{-1}, \Delta H^{\circ}_{(N-H)} = 389 \ kJ \text{ mol}^{-1})$

The bond energies of $H-H$ and $Cl-Cl$ are $430 \, kJ \, mol^{-1}$ and $242 \, kJ \, mol^{-1}$ respectively. $\Delta H_f$ for $HCl$ is $-91 \, kJ \, mol^{-1}$. The bond energy of $HCl$ will be ............. $kJ \, mol^{-1}$.

Calculate the enthalpy of formation of ethylene $(C_2H_4)$ from the following data:
$(I)$ $C_{\text{(graphite)}} + O_{2(g)} \longrightarrow CO_{2(g)}$; $\Delta H = -393.5 \ kJ$
$(II)$ $H_{2(g)} + \frac{1}{2} O_{2(g)} \longrightarrow H_2O_{(l)}$; $\Delta U = -256.2 \ kJ$
$(III)$ $C_2H_{4(g)} + 3 O_{2(g)} \longrightarrow 2 CO_{2(g)} + 2 H_2O_{(l)}$; $\Delta H = -1410.8 \ kJ$ (in $kJ$)

Based on Hess's law calculations,what is the average $S-O$ bond energy in $SO_3$ if $\Delta H_f^o$ of $SO_3$ is $-270 \ kJ \ mol^{-1}$. Given: Bond energy of $O=O$ is $495 \ kJ \ mol^{-1}$,heat of sublimation for $S_{(s)}$ is $277 \ kJ \ mol^{-1}$,and bond energy of $S=O$ is not provided,but we assume the formation reaction: $S_{(s)} + \frac{3}{2} O_{2(g)} \rightarrow SO_{3(g)}$. Use the atomization energy of $S_{(s)} = 277 \ kJ \ mol^{-1}$ and $O=O = 495 \ kJ \ mol^{-1}$. Calculate the average $S-O$ bond energy in $SO_3$.

The heat evolved in the combustion of benzene is given by the equation $C_6H_{6(l)} + 7.5 O_{2(g)} \to 3H_2O_{(l)} + 6CO_{2(g)}$,$\Delta H = -781.0 \ kcal \ mol^{-1}$. Which of the following quantities of heat energy will be evolved when $39 \ g$ of benzene is burnt in an open container?

The bond energies of $H-H$ and $Cl-Cl$ are $430 \, kJ \, mol^{-1}$ and $240 \, kJ \, mol^{-1}$ respectively. If the value of ${\Delta _f}H$ for $HCl$ is $-90 \, kJ \, mol^{-1}$,then the $H-Cl$ bond energy is ..... $kJ \, mol^{-1}$.