A system does 394 J of work on surrounding by absorbing 701 J heat. What is the change in internal energy of the system?

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 $$(\mathrm{N} \equiv \mathrm{N})=941 \mathrm{~kJ},(\mathrm{H}-\mathrm{H})=436 \mathrm{~kJ},(\mathrm{N}-\mathrm{H})=389 \mathrm{~kJ}$$ ?

What is the difference between $$\Delta H$$ and $$\Delta \mathrm{U}$$ for reaction given below at $$298 \mathrm{~K}$$ ?

($$\mathrm{R}=8.314 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}$$

$$2 \mathrm{C}_6 \mathrm{H}_{6(\ell)}+15 \mathrm{O}_{2(\mathrm{~g})} \rightarrow 12 \mathrm{CO}_{2(\mathrm{~g})}+6 \mathrm{H}_2 \mathrm{O}_{(\ell)}$$