Show how Equations 18.7 and 18.9 can be added to give Equation 18.10.

Video transcript

welcome back everyone. We need to select the correct edition of equations one and two to get equation three. So looking at equation one compared to equation three, we should recognize that we need two moles of phosphorus oxy chloride. Where in the first equation we only have one mole of phosphorus oxy chloride. We also should recognize that between equations one and three, we have an equation 31 mole of oxygen, whereas in the first equation we have a half mole of oxygen. So to correct these two variations, we want to go ahead and take this first equation and multiply it by two. And so this would now give us two moles of phosphorus oxy chloride plus two moles of chlorine, producing two moles of phosphorus Penta chloride and one mole of oxygen gas. Our next step is to compare the second equation to the third equation. So in the second equation we should recognize that we only have two moles or one mole of phosphorus Penta chloride, where in the third equation we have two moles of phosphorus Penta chloride. We also need to recognize that in our final equation, we do not have any phosphorus Penta chloride and so we want to cancel the phosphorus Penta chloride out. However, we would only be able to do so if in the second reaction it occurs on the opposite side, so it would need to react be a reacting actually. And so what we should do is take this second equation and we want to multiply it by two so that we get the proper moles of phosphorus tri chloride being two moles. And we want to also reverse reverse the reaction. And so this would now give us a reaction where we have phosphorus Penta chloride as a reactant which produces two moles of phosphorus tri chloride. And this would give us, sorry, two moles of phosphorus pencil chloride, because we were multiplying everything by two, Added to two moles of chlorine. And now that we've manipulated equations one and two to the best ability to get two. Equation three, we can now add these two equations together to see if we get our final equation. And so we want to cancel out everything that appears the same, but on opposite sides of each equation. So we can cancel the two moles of phosphorus Penta chloride from the product side in the first equation and from the reaction side in the second equation, we can also cancel out the two moles of cl two in the first equation, on the reactant side, with the two moles of cl two in the second equation, on the product side. And now we're left with everything else to get to our final equation where we have two moles of phosphorus oxy chloride which produces Our product two moles of phosphorus tri chloride plus 02. And so as you can see our manipulations above were able to give us our third equation. And so we want to see which reaction or which answer choice below. A B C or D gave us that choice and analyzing all the way down to choice D. We would see that the only answer choice which showed our reaction being reversed for the second reaction as well as both reactions being multiplied by two, is choice D, which gives us our final third equation here. And so that means that D. Is the only correct answer choice to complete this example. So D would be our final answer. I hope that everything I review was clear. If you have any questions, please leave them down below and I will see everyone in the next practice video.