 So we're going to do another example this time. I'm going to just do this straight out following the rules just from my memory So we're going to start by writing the half equations So we've got CR 2, 0, 7, 2, minus, goes 2 CR 3 plus and Hg Going to Hg 2 plus All right, so first step balance for everything other than hydrogen and oxygen I've got two chromiums on this side and only one on that side So we need to have two chromiums on that side. If I look at my mercury, I've got one mercury on both sides That's okay Next step balance for oxygen by adding water So I've got seven oxygens on the left hand side of here none on the right hand side So I need to add seven water molecules to the right hand side over there Look again down mercury one nothing much is happening there Next I need to balance for hydrogen by adding hydrogen ions where appropriate So I've got 14 hydrogen ions 14 hydrogens over here. So seven times two. So it means I need to add 14 Hydrogen ions to the left hand side Again, if I look down the bottom, I don't have any hydrogen to worry about Next step we're going to balance for charge by adding electrons So my total charge on the left-hand side over here, we've got plus 14 minus 2 so a total charge of plus 12 And if I look on my right hand side, I've got a total charge of two times plus three So I've got a total charge of plus six So that means I need to add six electrons to this side All right, so there's my six electrons All right, if I look at my bottom equation I've got a charge of zero on the left hand side and a charge of plus two on the right hand side So I'm going to add two electrons to the right-hand side So now we need to get the same number of electrons in both equations So I've got six at the top only two down the bottom. So I need to times the bottom by three. So I get three Hg goes to three Hg Two plus plus six electrons Now we cancel out what we can and add everything together So I've got six electrons at the top six electrons down the bottom that I can get rid of and that's about all we can cancel out So now we write down everything that we've got left over 14 H plus plus CR 2 07 2 minus plus 3 Hg goes to 2 CR 3 plus plus 7 H2o plus 3 Hg 2 plus All right Now we can check to see that we've got everything on the right sides and that we're all balanced So we'll start by charge. So we've got plus 14 minus 2 So we've got a total charge so plus 14 and minus 2 so tell charger plus 12 on the left-hand side On the right-hand side, you've got plus six plus another six. I've got plus two on the right-hand side So they're all balanced there next we'll check to see what atoms we have. So we've got 14 H plus we got 7 times 2 so 14 H plus I've got seven oxygens I've got seven oxygens three Mercury's three Mercury's two chromium is two chromium. So we're all balanced there