Nitrogen gas, $N_2(g),$ and hydrogen gas, $H_2(g),$ are suspected to be two important components of the primitive Earth. These two substances could have reacted to form ammonia $N{H}_3(g)$ in the atmosphere according to this reaction: $N_2(g)+3H_2(g)2N{H}_3(g).$

List different factors may affect whether the reaction between nitrogen and hydrogen will occur.