For the reaction, CaCO₃(s) → CaO(s) + CO₂(g) △H = 82.8 kJ at 25°C, △U at 25°C is

For spontaneous process △G < 0

For reversible process △G = 0

Work depends on the path followed by the system so work is path function.

$w=-nRTln\frac{V_2}{V_1}$

$\left|w\right|=2.303nRTlog\frac{V_2}{V_1}$

$\left|w\right|=1\times 2.303\times 8.314\times 300log\frac{100}{10}$        

|w| = 5744 J

|w| = 5.744 kJ » 6 kJ