The reaction of A with B to give D proceeds in two steps: (1) A + B → C ΔH° = -20 kJ (2) C + B → D ΔH° = +50 kJ (3) A + 2B → D ΔH° = ? (a) Which Hess's law diagram represents the reaction steps and the overall reaction? Diagram 1 Diagram 2

Video transcript

Hello everyone today. We have the following problem. Consider the formation of X and X forming which occurs in two steps shown below. Selected the Hess's law diagram that best depicts the individual reactions and the overall process. So for one we see that we have this first reaction and then we have this second reaction. If we notice the 1st and 2nd reaction add up to that third reaction there. We see this in that we have our W here in the reactant and R. W. And our products and then we have three X indicating that we added these two together, the two X. And the one X. To make three X. And then we have our to Z on our right side. So what happened to our two? I well the two eyes actually canceled out since they were on opposite sides of our reaction arrow. And so now we simply just have to add the Entropy changes together. So 100 -60 is going to give us 40 kill jules. And so now let's compare to see how these reaction arrows relate to our options. So for the first one they both are the same distance so we cannot count the first one for our answer. However, for our second one for our diagram A we noticed that too is in a positive direction whereas in diagram B two is in the negative direction. And so when delta H or entropy change is negative, our arrow is supposed to be pointing downwards as in diagram B. If we look at three we have a positive 40 kg joules and our arrow should be pointing up another way to figure out the answer. In this is to simply look at how the arrows compare arrow Based on our mathematics. Arrow three should be smallest smaller than Arrow two and one in diagram B, arrow three is smaller than arrow to however, in diagram a arrow three is larger than Arrow, too, and so therefore diagram B. It's going to be our answer that best depicts the individual reactions and the overall process overall. I hope that this helped, and until next time.