4.1: Collision THeory
Basic Principle: for things to react, they must first collide with enough energy, and in the right orientation.
Bimolecular collisions are much more likely than trimolecular collisions. Termolecular collisions (4 molecules) are nigh-impossible.
You can make collisions more likely by increasing concentration (which, for gasses, can be accomplished by raising pressure), or by increasing the temperature to speed up the molecules.
You can make collisions have more energy by increasing the temperature.
The likelihood of collisions will determine how fast the reaction goes; this is COMPLETELY separate from thermodynamics, which determines whether it will go or not.
Examples of collisions: