The negative change in concentration of y over BT gives you the rate of disappearance of Y. Now, the rate of appearance of W and Z can be given by these formulas where now we have the positive because these guys appear and so these guys will both be positives. Now, let's look at the factors affecting our reaction rates. So, we already said that temperature affects our rates of reaction because it affects our rate constant. Now, if the rate constant increases, then our rate of reaction increases. And we'll see why at the end of this lecture.