One kg of air ($${R = 287\,\,J/kg}$$-$$K$$) under goes irreversible process between equilibrium state $$1\,\,\left( {{{20}^ \circ }C,\,\,0.9\,\,{m^3}} \right)$$ and equilibrium state $$2\,\,\left( {{{20}^ \circ }C,\,\,0.6\,\,{m^3}} \right).$$ The change in entropy $${s_2} - {s_1}$$ (in $$J/kg$$-$$K$$) is _________