4.21     explain that a catalyst speeds up a reaction by providing an alternative pathway with lower activation energy.

A catalyst provides an alternative reaction pathway with a lower activation energy, i.e., an easier route to the products.  At a given temperature, more  particles will  have  enough  energy  to react on  collision, so there will be more successful collisions per second. Note that particles have not been given more energy - they just don’t need as much to react on collision.  Particles have the same kinetic energy whether a catalyst is present or not, as long as the temperature is the same.