Which of the following is balanced chemical equations for the synthesis of nabr from na and br2

2Na + Br2 -> 2NaBr
Br is a diatomic element so the 2 is a subscript, not a coefficient.

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.