At low temperatures, none of the particles have sufficient energy to surmount the activation barrier. This changes as the temperature is gradually increased. The reaction rate depends on the frequency of collisions, the amount of energy in the particles during collisions, and the relative orientation of particles during collisions. At any given temperature there are always a collection of particles that have enough energy to overcome the activation barrier. The order of the reaction generally reflects the number of molecules that collide during reaction. All of the above are true.