Fig 8The energy barrierenergy along the reactionuncatalysed
catalyst
Even a reaction that releases energy has to climb a barrier first, because old bonds must start to break before the new ones form. That barrier, the activation energy, is why paper sits in air without catching fire until a match heats it. A catalyst offers a different route with a lower barrier, so the reaction runs much faster at the same temperature, but it doesn't change where the reaction starts or ends, so it releases the same heat.