ontaneous. (a) 2NH3(g)3H2(g)+N2(g)Hrxn=+91.8kJ/mol sign of Ssys : positive negative sign of Ssurr : positive negative spontaneity: spontaneous at all temperatures spontaneous only at low temperatures spontaneous only at high temperatures not spontaneous at any temperature (d) C2H5OH(I)+3O2(g)2CO2(g)+3H2O(g)Hrxn=1234.8kJ/mol sign of Ssys : positive negative sign of Ssurr: : positive negative spontaneity: spontaneous at all temperatures spontaneous only at low temperatures spontaneous only at high temperatures not spontaneous at any temperature