A gas expands isothermally against a constant external pressure of 1 bar from 10 dm$^3$ to 20 dm$^3$ by absorbing 800 J of heat from surrounding. Calculate value of $\Delta$U.

Which of the following equations indicates increase in entropy?

Which from following statements is true about internal energy?

2 moles of an ideal gas are expanded isothermally and reversibly from 20 L to 40 L at 300 K . Calculate work done. ( $\mathrm{R}=8.314 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}$).