is there a universal method to knowing this.
Briefly, no. As everyone else has said. The question now remains, what specifically do you need to do, so we can figure out how to explain it to you. The other question, why you thought there was a universal method to all understanding all chemical reactions -- from the weathering of rocks over millenia, to the rusting of iron, to biological reactions needed for life to continue, to explosions, well, that's all up to you to explain.