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

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

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

When 1 mole of gas is heated at constant volume, the temperature rises form $$273 \mathrm{~K}$$ to $$546 \mathrm{~K}$$. If heat supplied to the gas is $$\mathrm{x~J}$$, then find the correct statement from following.

What is the value of $$\mathrm{\Delta H-\Delta U}$$ for the formation of 2 moles of ammonia from $$\mathrm{H_{2(g)}}$$ and $$\mathrm{N_{2(g)}}$$ ?

Two moles of an ideal gas are expanded isothermally from $$15 \mathrm{dm}^3$$ to $$20 \mathrm{dm}^3$$. If the amount of work done is $$-6 \mathrm{dm}^{-3}$$ bar, find external pressure needed to obtain this work.