A Beginner’s Guide to Balancing Equations


Mr. Andersen explains the basics of balancing chemical equations. A visual guide shows you how to change coefficients to balance the atoms in reactants and products.


Transcript Provided by YouTube:

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My beginner’s guide for balancing equations. The first thing that I want to
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let you know is that there’s no magic to balancing equations. There’s no secret that you can
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somehow pick up and all of a sudden become a guru. The reason I made this video is that
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some students just seem to struggle with how do I even do that or the concept behind it.
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And so if you’re really have troubles, hopefully I can kind of clear some of that up. And if
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you’re not, this is probably not the video for you. I would just go google balancing
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equations practice and you’ll find some really hard ones out there that you can try your
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hand at. So let’s get started. The first one we’re going to talk about is the combustion
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of hydrogen. This is the Hindenburg explosion and after this we quit putting hydrogen gas
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into blimps for obvious reasons. But essentially what happens is hydrogen combines with oxygen.
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Okay, so if we look at the equation down here at the bottom, the equation as it is
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H2 + O2 yields water or H2O and we’re going to get a lot of energy out of there as well.
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Now the first thing we need to talk about is what these numbers actually mean. So this
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2 down here is a subscript and that means that it tells you how many atoms of hydrogen
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are in a molecule. And so this is what the molecule of hydrogen would look like. We’re
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going to have two atoms of hydrogen. The thing that you need to remember is you can never
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change the subscript. Subscripts have to remain the same. Because if you change it, you’re
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changing what that molecule actually is. And so this would be H2, this would be O2, so
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we have two oxygen molecules attached together, then finally we have H2O. H2O is one oxygen
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and two hydrogens on either side. And so when I look at this, a lot of people will just
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try to go and answer this but maybe we need to step back a little bit and actually look
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graphically at what’s going on here. And so when I look at this I can see here’s reactants
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before the reaction and products. And so just looking at it when these are graphically shown
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you can see that I have two of these red oxygen atoms on the left side and only one on the
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right. And so the first thing you might want to do is kind of double that. And so let me
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do that. Okay, so now visually we’ve got two water molecules and so I’ve got two reds on
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the right side and two reds on the left side. You’ll also notice, so that’s balanced, that
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the hydrogens are changed. And so I have four hydrogens on the right side but I only have
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two on the left side. So now let me click it again and we’ve got a balanced equation.
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In other words, I can never change the subscripts, I can never change what these molecules are
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but when you’re balancing equations what you’re trying to do is add more of the molecules
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so you can see that reactants and products will be balanced. Okay. Now how do we actually
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write that out? So we can put in front of here what are called coefficients. And coefficients
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are numbers in front of the molecule that tells you how many there are. And so there
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is one oxygen and we never write the coefficient of one. And so you don’t want to write one
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as a coefficient. If it’s a coefficient of one you just leave it blank. But let’s go
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over here to H2. You’ve got this H2, that H2 and so you have 2 H2. So that would be
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on the left side. If we go onto the right side you have this molecule of water, this
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molecule of water and so we have two molecules of water on the right side. And so if we step
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through this, this means we have two molecules of H2, so that would be 4 hydrogens on the
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left side. After you balance an equation you want to go back and look at it to make sure
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it’s balanced. Over here we have 2 H2s as well so we have 4 hydrogens. We have 2 oxygens
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on the left side, and we have 2, this coefficient multiplies this whole thing, so we have 2
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oxygens on the right side as well. And so we would call that a balanced equation. And
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so hopefully just by looking at it graphically that might help a little bit. Let’s go to
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the next one. The next one in a chemistry lab is, you see it all the time, this is a
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Bunsen burner. And these are some flames from a Bunsen burner. And so a Bunsen burner works
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using a gas called methane. And methane is CH4. So if we took a look at methane, methane
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looks like this right here. It’s got one carbon molecule and then it’s got four hydrogens
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attached around the outside. And when we burn methane, what that really means is that we’re
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combining methane with oxygen and we’re creating these two things in complete combustion. We’re
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creating some carbon dioxide (CO2) gas, that’s one carbon, two oxygens and then we’re creating
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a little bit of water (H2O). The other thing we’re going to produce is going to be energy.
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Okay. So if you look at this just graphically on the left side and on the right side, the
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first thing, at least to me that jumps out is that there is way more hydrogen on the
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left side then the right side. So the first thing I could do would be to add another water
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on the right side. So if I add another water on the right side, the yellow balls on the
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right now match the yellow balls on the left. The carbon, there’s only one on the left,
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matches the one on the right. So we must be getting really close. But I’ve got four reds
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on the right and only have two. And so I have to add that as a whole molecule, so if I made
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one more molecule of oxygen, now we have a balanced equation. So how do we write that
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out? So methane on the left side, I have one methane but I’m not going to right the number
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one. How many molecules of oxygen do we have? We have two. So I’m going to put a 2 as a
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coefficient right here. Now on the right side we only have one carbon dioxide, so I’m not
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going to put a one. But there should be in your mind a 1 there. Then how much water do
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we have? We have just two waters. So I’m going to put 2 right here. Now we could go through
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the whole thing. So how many carbons do we have? One on the left, one on the right. How
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many hydrogen do we have? Four on the left. And this 2 is multiplied by the subscript,
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so we’ve got 4 on the right and 4 on the left. And then if we look at oxygen, we’ve got 4
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on the left and then we’ve got 2 oxygen here and we have 2 oxygen there. And so when I’m
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solving and trying to balance equations, I’m not really seeing these, but if that helps
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you visualize it then it will help you do better at that. So let’s try it. So the only
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way to get better at this is to just practice. And so let’s try a few and I will show you
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how I would think through this in my mind. So if we look at the first one, this H2O2
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which is hydrogen peroxide. It breaks down into hydrogen gas and oxygen gas. Okay. So
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how would I set this up. Well on the left side we’ve got H2. So if I want to write it
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out I could. So I’ve got 2 hydrogens on the left and as far as oxygens on the left I’ve
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got 2 oxygens as well. And so on the right side how many hydrogens do I have? I have
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2 on the right and I have 2 on the left as well. And so this already is a balanced equation.
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And so what do you do if you find a balanced equation that’s already balanced? You don’t
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do anything to it. In other words we’d write a 1 in front of each of those but we never
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write ones so I’m going to leave that one the way it is. Let’s go to the next one. On
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the left side we’ve got sodium (Na), we’ve got chlorine gas (Cl2) and then we’re making
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table salt. And so if you want to write this out you could. We’ve got Na and I’ve got 1
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of those. I’ve got chlorine on the left side and I’ve got 2 of those. So that’s on the
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left side. That’s on the reactant side. Now let’s go to the product side. How many sodium
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do we have? We only have one sodium. And how many chlorine do we have on the right side?
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Well, we only have 1 chlorine so that’s a problem because on the product side we only
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have 1 atom of chlorine and on there reactant side we actually have 2. So how could I fix
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that? Well, let’s try to go back. Let’s say I’ve got too few chlorine on this side, so
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let me just try and add the next step which is to add a 2 on the right side. So by adding
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a 2 on the right side I’ve taken care of my chlorine, so on the right side now I have
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2 sodium and 2 chlorine. But I’ve set up another problem. In other words I have 2 sodium on
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the right side so now I have to balance that over here. And so I’m going to come back over
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here and write a 2 over here which makes this a 2. Okay so now we’ve got 2, 2, 2, 2 and
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that’s balanced. And so the right answer for that one is to put a 2 in front of the sodium
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(Na) and then a 2 in front of the sodium chloride (NaCl). And that’s a balanced equation. Remember
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you can never change the subscript. Alright. Let’s do another one. And so these are getting
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progressively harder and so I’ll give you some tips as far as that goes. The first tip
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would be this. If we look at this one we’ve got silver sulfide (Ag2S), Silver (Ag) and
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Sulfur (S8). So this 8 jumps out right away. So on the right side I’ve got 8 sulfur atoms.
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If we look on the left side I’ve only got 1. And so as a bare minimum I’m going to try
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writing an 8 right here and let’s see what that does. Well now we have 8 sulfur on the
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left side, 8 sulfur on the right side, but our silvers aren’t matching. So on the left
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side we actually have 16 silver but on the right side we only have 1. And so let me trying
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just writing a 16 down. So now that’s a balanced equation. So we could go through. 16 silver,
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16 silver, 8 sulfur, 8 sulfur and that’s going to be a balanced equation. The nice thing
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about balancing equations is you can always check it at the end and you know that you
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are right. It’s not like maybe you’re right, you absolutely are right as long as you’re
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just adding the coefficients. Alright. So here’s the ones that are more likely that
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you’re going to find. And so let’s work through this and always be patient remembering that
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if you get frustrated you can just erase them all. Start over again. You should be able
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to figure them all out. It’s just kind of a guess and check. But let me show how I would
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think this one out. So I’ve got water (H2O), carbon dioxide (CO2), got a hydrocarbon (C7H8)
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here and then we’ve got an oxygen (O2). And so on the right side, the thing that jumps
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out to me right away is we’ve got 7 carbons on the right side and so what I’m going to
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try to do is put a 7 over here. Okay. So what does that do for me? Now I’ve got my 7 carbons
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taken care of. The other thing that jumps out right away is on the right side I have
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8 hydrogens and water is the only thing on the left side that actually has hydrogens.
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And so there’s an 8 here and let me try putting a 4 over here. Okay, so what that does is
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give me hydrogen on the left is going to get me 8. Hydrogen on the right side is going
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to get me 8 as well. Now I love it when I solve these and I get down to just like one
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thing left and it has one atom in it. And so I think carbons and hydrogens are good
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on either side but let me take a look at the oxygen. On the left side we have 4 oxygens.
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So in this molecule of 4 waters. And then we have 14 here. So I’ve got 14 total oxygen,
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14 here and 4 then over here, and so how do I get to, so again I’ve got 18 total, and
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so if I were to put a 9 over here, that would give me on the right side 18 total oxygens.
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On the left side 18 total oxygens as well. So that would be a perfectly balanced equation.
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And so that’s kind of my starter’s guide on how to balance equations. Remember you can
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only add the coefficient. You can never change the subscripts. And if you get confused, start
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imagining them as molecules and even draw them out if you have to and that might help
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a little bit. So I hope that’s helpful and have a great day.\
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This post was previously published on YouTube.

Photo credit: Screenshot from video

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