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

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

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

Enthalpy of formation of methane is $$-$$75 kJ/mol. What is the enthalpy change for formation of 24 g of methane?

The expansion of gas having no opposing force is called as

1 mole of an ideal gas expands isothermally and reversibly by decreasing pressure form $$210 \mathrm{~kPa}$$ to $$105 \mathrm{~kPa}$$ at $$300 \mathrm{~K}$$. What is the work done? $$\left(\mathrm{R}=8.314 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\right)$$