a reaction mechanism is a step by step sequence of elementary steps, by which an overall chemical change occurs. Now, when we use the term elementary step, an elementary step is just one step in a series of reactions that show the progress of a reaction at the molecular level. Now here we're gonna have a reaction mechanism overview. So we're gonna stay here step one and step to represent our two elementary steps. So this would be elementary step one. An elementary step two. In elementary step one, we have cl gas plus O three gas, giving us cielo gas plus O two, gas. In elementary step two, we have cielo gas plus cielo gas, gives me cl gas plus C L +02 gas. Now, both elementary steps together. Well, that represents our reaction mechanism. So these two elementary steps together, our reaction mechanism. And we can say here that our overall reaction can be created by canceling out what we call our catalysts and reaction intermediates. So if we take a look here, we're going to say that a catalyst is a compound shown as a reactant in the first step, and then as a product in the final step. So here the first step is just elementary step. One final step is elementary step two. Now, if this mechanism of another mechanism we see has let's say four elementary steps, then the first step would still be the initial step and it will be the very last one. Step four, that would be our final step. Okay, but in this case, since there's only two, this is the first step. This is the second step. Now our reaction intermediate. This is a compound that first appears as a product in one elementary step, and then later as a reactant in another elementary step. Now these are canceled out and by counseling them out. What's left behind comes down to form our overall reaction. So if we looked at the overall reaction, this would come down here. This came down here, this came down here and then this came down over here. So keep this in mind. When you're looking at a reaction mechanism, a reaction mechanism is just all of the elementary steps together. If we were to cancel out our catalysts and our reaction on our reaction intermediates, that should give you the overall reaction for the equation. Okay, so just keep this in mind these key terms when it comes to any type of reaction mechanism and elementary step.