If the rate is a large number then the reaction is very, very slow. A chemical explosion is a very fast chemical reaction that releases energy. The nitrogen gas that is formed very quickly fills up the airbag. An increase in temperature increases the reaction rate. As you increase temperature you increase the kinetic energy of molecules.
Reactions can only occur if molecules get close enough together to collide.
The smaller the subdivision of materials the faster the reaction rate. The smaller the pieces, the more surface are. The increased surface area means that you have a greater chance for collisions to take place. The higher the concentration of reagents, the faster the reaction rate. The higher the concentration, the closer the molecules and therefore the greater chance for collisions.