Chemical Thermodynamics Chapter 4 Chemistry Class 12 Textbook Solution

1. A free expansion occurs when a gas expands in a vacuum where there is no opposing force (P_ext = 0).
2. During such an expansion, the work done by the system is given by:
   \( W = - P_ext \Delta V = 0 \)
   Thus, no work is done when a gas expands freely in a vacuum.

Note: Units of energy and work:

1 Joule (J) = 1 kilogram-meter² per second^-2 = 1 Pascal (Pa) meter³

1 Pascal (Pa) = 1 kilogram per meter per second^-2

When the pressure is expressed in bar and ΔV in decimeters cubed (dm³), then the work has units of bar dm³.

1 bar = 10⁵ Pa = 10⁵ kg per meter per second^-2

1 dm³ bar = dm³ × 10⁵ kg per meter per second^-2

= meter³ × 10^-3 × 10⁵ kg per meter per second^-2

= 100 kilogram-meter² per second^-2 = 100 Joules (J)