The reversible reaction, 2NO{g) ⇌ N2 (g) + O2 (g), would be classified as a reaction. homogeneous
heterogeneous
endothermic

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.

Temperature and pressure

The answer should be vaporization