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

4.19 •activation energy represents the minimum energy needed by reacting particles for the

         reaction to occur

                  •a catalyst makes the reaction happen faster by providing an alternative reaction

                   pathway (i.e another way for the particles to react) with a lower activation energy 

                            •this is shown by the lower curve on the diagram, which shows that less initial energy is needed for the reaction to begin 

                                      •the overall energy change for the reaction remains the same