Two moles of an ideal gas is expanded isothermally from a volume of $300 \mathrm{~cm}^3$ to 2.5 $\mathrm{dm}^3$ at 298 K against a constant pressure at 1.9 bar. Calculate the work done in joules.

Calculate heat required to convert 9 g of liquid water to water vapours from following equations.

$$\begin{aligned} & \mathrm{H}_{2(\mathrm{~g})}+\frac{1}{2} \mathrm{O}_{2(\mathrm{~g})} \longrightarrow \mathrm{H}_2 \mathrm{O}_{(\mathrm{g})} \Delta \mathrm{H}=-57 \mathrm{kCal} \\ & \mathrm{H}_{2(\mathrm{~g})}+\frac{1}{2} \mathrm{O}_{2(\mathrm{~g})} \longrightarrow \mathrm{H}_2 \mathrm{O}_{(\mathrm{g})} \Delta \mathrm{H}=-68.3 \mathrm{kCal} \end{aligned}$$

One mole of a gas occupying 3 L volume is expanded against a constant external pressure of 1 bar to a volume of 15 L . Calculate work done by the system

Which from the following defines enthalpy of a system?