What is the heat of formation of $$\mathrm{HCl}_{(\mathrm{g})}$$ from following equation?

$$\mathrm{H}_{2(\mathrm{~g})}+\mathrm{Cl}_{2(\mathrm{g})} \rightarrow 2 \mathrm{HCl}_{(\mathrm{g})} \Delta_{\mathrm{f}} \mathrm{H}=-194 \mathrm{~kJ}$$

If $$\mathrm{Q}$$ is the heat liberated from the system and $$\mathrm{W}$$ is the work done on the system then first law of thermodynamics can be written as,

Formation of $$\mathrm{NO}_{2(\mathrm{g})}$$ from $$\mathrm{N}_{2(\mathrm{g})}$$ and $$\mathrm{O}_{2(\mathrm{g})}$$ is an endothermic process. Which of the following is true for this reaction?

What is enthalpy of formation of $$\mathrm{NH}_3$$ if bond enthalpies are as $$(\mathrm{N} \equiv \mathrm{N})=941 \mathrm{~kJ},(\mathrm{H}-\mathrm{H})=436 \mathrm{~kJ},(\mathrm{N}-\mathrm{H})=389 \mathrm{~kJ}$$ ?