 Today, I'd like to talk to you about mole ratios and its relationship to energy. We all know that when we have food to eat, that the more food we eat, the more energy we get out of it. Well, chemical reactions are not that much different than eating food. In fact, you can say that our food breakdown is a chemical reaction. But what you may not understand is that there is a finite amount of energy that can be given off by any chemical reaction. And so we'd like to talk about that just briefly this morning. If we look at this chemical reaction, which is the reaction or combustion of hydrogen with oxygen to form water, we see that our delta H, which is our energy that's given off for this reaction, is a negative 364 kilojoules per mole. How we can write this or say it another way is that two moles of hydrogen would convert or combust to give us negative 364 kilojoules of energy. You can also say that in this reaction, one mole of oxygen would give you the same quantity of energy. And so we can ask ourselves this question, what if we didn't have the same ratios here of these materials? How would that affect the amount of energy that we would get from this reaction? Suppose I told you that we didn't have just two moles of hydrogen, but rather we have four moles of hydrogen. How would we determine the amount of energy that we would get from using four moles of hydrogen? We need to understand here that when I say four moles of hydrogen, I'm saying this, that we have four moles of hydrogen and we have plenty of oxygen to react with it to completely convert it to water. Thus, hydrogen would not be left within our process. If that is the case, then here's how we would set that up. We would say we have four moles of hydrogen times negative 364 kilojoules for every two hydrogens. The two comes from this coefficient here. And the answer to our question then would be that from four moles of hydrogen we would double the amount of heat that would be emitted and we'll have a negative 728 kilojoules of energy. Now, let's think about this from a different direction. Notice that instead of having knowing how much reactants we had, we simply knew the amount of energy that we got out of the reaction. And let's say that we had an unknown mixture which had plenty of oxygen available and wanted to know how much hydrogen was reacted. What if I told you that we had a negative 182 kilojoules of energy per mole? A negative 182 kilojoules of energy that was emitted by the reaction. And we were trying to determine how much hydrogen was reacted. We go back to our equation again and we say that there's two hydrogens for every 364 kilojoules of energy. In this instance then it would mean that we would only react one mole of hydrogen. So we can use energy as a way of calculating the amount of chemical that has reacted. We can also predict based on the amount of materials that are present how much energy will be given. Is this practical? The answer is yes, it's practical. And not only is it practical, it's something that's important for this reason. There are systems that we use every day that would have limits to the amount of energy or the amount of heat that they can take at any given time. So engineers use these sorts of calculations to design our automobiles, our airplanes, many things that emit or use energy. And so as you move forward think about this process and also think about your bodies because the chemical reactions that take place within our bodies when we consume food are not greatly different than these. I hope that you've learned something from this this morning and thank you.