Two moles of an ideal gas expand reversibly and isothermally at $300 K$ from $5.0 L$ to $20 L$ . Taking $R = 8.314 J mo l^{- 1} K^{- 1}$ , the work $w$ (IUPAC sign convention, work done on the system) is

Answer: C

For a reversible isothermal process

w = - n RT ln (V_{2} / V_{1}) = - (2) (8.314) (300) ln 4 = - 6915 J = - 6.92 kJ

. The sign is negative because the gas does work. Using

lo g_{10}

in place of

ln

V_{2} / V_{1}

directly gives the wrong magnitudes.