Lesson video

Hello, my name's Mrs. Nevin, and today we're going to be talking about balancing equations as part of our unit on calculations involving masses.

Now, you may have some experience of this from your previous learning, but what we do in today's lesson is essential for any chemist going forward, because what it's going to do is not only help us to better understand and answer that big question of what are substances made of, but it helps us to better communicate with other chemists and other scientists what's going on in a chemical reaction in a far more detailed way.

But more than that, it's forms the basis for us to be able to make more detailed discussions about what is facing society at large.

For instance, climate change is widely discussed and debated at the moment, and some airlines are actually offering people the chance to offset the amount of carbon dioxide that's produced from one of their flights.

For instance, if somebody's travelling from London to Athens or from Manchester to Florida, a balanced equation will help us to calculate the amount of carbon dioxide that might be produced during that flight.

And then it would also help us to decide, hmm, how many trees might we need to plant in order to offset the amount of carbon dioxide that's produced? And all of those answers start with an understanding of the balanced equations representing those reactions that take place during those activities.

So let's get started.

By the end of this lesson, you should hopefully feel more comfortable balancing a chemical equation and explaining why it's important to ensure that symbol equations are balanced.

Throughout the lesson, I'll be referring to some key words, and these include word equation, chemical formula, symbol equation, balance symbol equation, and coefficient.

Now the definitions for these keywords are provided in sentence form on the next slide, and you may wish to pause the video here so that you can make a note of these definitions that you can then refer to later on in the lesson or later on in your learning.

So today's lesson is broken up into two parts.

The first part we'll look at the different ways that we can represent chemical reactions, and the second one we'll look at specifically how we balance symbol equations.

So let's get started by looking at the different ways that we can represent a chemical reaction.

Now, anyone has done any cooking or baking will be familiar with recipes, and they'll know that recipes provide a lot of information.

For instance, they're going to indicate the ingredients that are needed, and it will tell you how much of each is required.

A recipe will also tell you what you're making and how much you can expect to make.

Now a chemical equation then is simply the recipes that are used in chemistry and they indicate what's needed and what's made.

So we look at this particular reaction of magnesium plus oxygen makes magnesium oxide, it's telling me what's needed and what I can expect to make.

Now this is an example of a word equation, and a word equation represents reactions by providing the names of my reactants and the names of my products.

And they're incredibly useful for those people who are new to chemistry and who use the same language that it's represented in.

But there are a few downsides to representing a chemical reaction using a word equation.

For instance, it's not universally understood.

This same equation written in English as magnesium plus oxygen makes magnesium oxide would look like this in Greek, and I'm afraid I'm not going to attempt to pronounce that because I don't speak Greek.

It also doesn't provide very much information about the atoms that are involved or the ratios of the substances that are involved because it doesn't contain any values.

So it's not telling me how much I need or how much I can expect to make.

Let's stop here for a quick check.

What are two reasons to represent a reaction using a word equation? Well done if you said B and D.

We'd use a word equation because it's useful for people who are new to chemistry and it will tell us the names of those reactants and products that will be used.

So it's the simplest way to represent a chemical reaction.

Well done and great start guys.

Now symbol equations then are the next step up from a word equation.

Now they also are going to be able to indicate the reactants in products, but they do so using chemical formula.

So we have here again still our word equation of magnesium plus oxygen makes magnesium oxide.

But below it then we have taken those words, the names or chemical names and changed them into the chemical formula.

And again, it's still showing us the reactants that I need and the products that I'm gonna be making.

But there are some downsides to using symbol equations because you need to be able to actually understand what those elements are and what the state symbols mean.

You also need to be able to interpret that chemical formula in order to be able to understand what a symbol equation is telling you.

So why do it then? Why represent a chemical reaction using chemical formula, using those symbols? Well, there's a very good reason for this.

Because what it does is it's going to represent the elements that are present using those symbols.

So rather than just the words, we can identify the elements that are involved.

And more than that, it also tells us the ratio of the atoms in each substance.

So I can interpret my symbol equation as showing one magnesium atom will react with two oxygen atoms, and it will make something that is composed of one magnesium and one oxygen based on those formula that I get from my symbol equation.

Now if we take that symbol equation and balance it using coefficients, I get even more information that I can use about that chemical reaction that's taken place.

So again, we go back to that magnesium and oxygen, making magnesium oxide, we've got our word equation and our symbol equation.

The coefficients then are those big numbers that come before the chemical formula.

And what they do is they indicate then the ratio of each substance in that reaction.

So for this particular reaction, I can say, because of the coefficients, I'm going to need twice as much magnesium as I have oxygen in order for this reaction to occur.

So despite there being some drawbacks to using a symbol equation, there are some really good reasons why we as chemists choose to use them.

For instance, it is universally understood.

The symbols that are used to represent our different elements are used across the world.

It doesn't matter what language you speak or read or understand.

The same is true then about the physical states of these substances that are involved.

So it includes those state symbols, which we didn't have in our word equation.

It's also going to include the chemical formula.

And remember these are telling me the ratio of the elements that are involved in each substance.

And it also when it's balanced, is gonna show me the ratio of the substances.

So how much do I need of each chemical for my reactants and how much can I expect to make then of my products? Let's stop here again for another quick check.

True or false, ratios of atoms in a substance are shown using coefficients.

Well done if you said false.

But which of these statements best justifies that answer? Well done if you said A.

The ratio of substances in a reaction are shown using coefficients, not the ratio of the elements, that's shown in a chemical formula.

Well done if you manage to choose false and the correct supporting statement.

You're doing really well, guys, keep it up.

Okay, time for today's first task.

What I'd like you to do is I'd like you to convert each description below into a word equation and only a word equation to start with.

What I'm gonna recommend is if you have two different colours to perhaps do all the reactants, highlight them, circle them, underline them, whatever, in one colour for the reactants and a different colour for the products.

If you don't have different coloured markers or pens, what you might like to do is to draw a square around the reactants and a circle around the product, something like that just to help guide you into transforming these descriptions into a word equation.

This might take a little bit of time, so if you'd like to pause the video here and come back when you're ready to check your answers.

Okay, let's see how you got on.

So I use that suggestion of using two different colours to identify my reactants and products.

And when I read, when magnesium reacts with hydrochloric acid, we form the salt, magnesium chloride and hydrogen gas.

So my reactant, so what I start with that's reacting together are magnesium and hydrochloric acid.

And what is formed then is the magnesium chloride and hydrogen gas.

So my word equation should look like this.

Remember, we're using an arrow, not an equal sign to distinguish between my reactants and my products.

For B then, sulphur dioxide gas is made when sulphur reacts with oxygen.

My reactants then are my sulphur and oxygen, and my product is sulphur dioxide.

So my word equation should look like this.

Sulphur plus oxygen, arrow, sulphur dioxide makes a sulphur dioxide.

And C then, the salt strontium sulphate, carbon dioxide gas and water are formed when strontium carbonate reacts with sulfuric acid.

It's quite a long one, but if I identify my reactants and my products, my word equation then should look like this, strontium carbonate plus sulfuric acid, arrow, or makes strontium sulphate plus carbon dioxide plus water.

Now remember your reactants and your products can be in whichever order you want them to be.

They don't have to match the order that I've put them on this slide, but it's really important they're on the correct side of the arrow.

So make sure that the strontium carbonate and the sulfuric acid are on the same left hand side of that arrow, and the rest are on the right in whichever order, as long as they're at the correct side of that arrow.

Great start guys.

Let's move on to the next part of today's task.

So the next step of converting a word equation into a symbol equation is making sure that you use the correct chemical formula for that chemical name.

So I have the names of some substances listed and I'd like you to match up the correct formula for that name.

Now be careful, there are a few red herrings in there that might mess you up.

So you might wish to discuss this with the people nearest you.

So pause the video and then come back when you are ready to check your answers.

Okay, let's go through how you got on.

Now, before we actually get started, can I just recommend that as we do go through these, if you have any that are incorrect, make sure that you are correcting them, and if you left any blank, make sure that you are putting the correct answers in that space because you're going to need the answers from this task for the next part, okay? So, magnesium is Mg, making sure you've got that capital M, lowercase G.

Hydrogen then is H2.

Remember that two should be small subscript.

Oxygen then is O2, so it's diatomic as well, but sulphur is just S.

Hydrochloric acid is HCl.

And the key there was hydro for hydrogen, chloric for chlorine.

So if you had your periodic table handy, you can find those symbols on there quick and easy.

Sulfuric acid was a tricky one, but it's H2SO4.

Sulphur dioxide, the di meaning two means SO2 then for my sulphur dioxide.

Water is a pretty common one, so H2O.

Carbon dioxide is CO2.

Magnesium chloride is MgCl2.

Strontium carbonate was SrCO3.

Again, be really careful that you've got your capital letters for the first part of that symbol and a lowercase letter, and that you've got those different sizes in there, okay? It's really important that your formula is clearly written.

And then your strontium sulphate should be SrSO4.

So take a moment just to double check you've got those formula correct, correcting ones that you've got wrong and filling in any ones that you've got blank.

But very well done if you manage to correctly use or match up the formulas and the names, guys, it's not an easy task, but really pleased with the work you guys have been doing, keep it up.

Okay, for the last part of this task, what I'd like you to do is go back to those word equations that we wrote in Task A Part 1, and we're gonna convert them into a symbol equation and try to include those states symbols as well.

To help you with this, you may wish to go back and use the formula that we matched up to those chemical names from Task A Part 2 to help you.

Once you've finished that, changing your word equations into our symbol equations with state symbols, go back through those symbol equations.

Do you think anything is missing or needs improving in any of them? And why or why not, okay? Now this is gonna take a little bit of time.

You may wish to confer with the people around you.

So pause the video here and come back when you're ready to check your answers.

Okay, let's see how you got on.

So for that first equation, it was magnesium plus hydrochloric acid makes magnesium chloride and hydrogen.

So all I'm gonna do then is take the formula for each of these chemical names and put them directly below their names.

So I should have Mg, and magnesium is a metal, so it's likely to be a solid.

That's why we've got S in brackets, plus hydrochloric acid, which was HCl.

Now it's tricky sometimes, you may have said it was a liquid, it's actually an aqueous solution, so it's normally dissolved in water.

Don't worry if you got that one wrong, it's a tricky one.

Most acids are an aqueous solutions, so there's something to think about going forward.

And then making magnesium chloride, which is MgCl2, it's a salt.

We've got a metal and a non-metal, therefore it's gonna be a solid, so that's why it's in S in brackets for its state symbol.

And then the hydrogen is a gas, that's H2.

And then we've got the subscript G in brackets to represent it as a gas.

So well done if you manage to get that one correct.

The second equation then, sulphur plus oxygen makes sulphur dioxide.

We should have an S, which is a solid, plus O2, which is a gas, makes SO2, which is also a gas.

Again, a tricky one if you weren't sure about sulphur dioxide as being a gas.

But well done if you managed to do that is a simple molecular structure.

And finally then we had strontium carbonate plus sulfuric acid, make strontium sulphate, carbon dioxide and water.

So changing those chemical names into formula, we should have something like this.

Now, strontium carbonate, we've got metals and non-metals.

So that makes me think it's an ionic substance and it's probably going to be a solid, that's why I've put it as a state symbol of S.

I said earlier that acids tend to be aqueous.

So again here, aq to show that it's dissolved in water.

Again with the strontium sulphate, I've got metals and non-metals, suggesting that it's ionic and probably a salt, therefore a solid.

Carbon dioxide we said is a gas, and water in its standard state is a liquid, which is why I've put an L.

So very well done if you manage to get firstly the symbols in the correct places to represent the different chemical names, and very well done if you manage to correctly identify the state symbols for each of those substances as well, guys.

It's not an easy task and you are doing absolutely brilliantly.

Keep it up.

So for the very last part of this task, I asked you to review those symbol equations and decide if you think anything was missing or anything might need improving in any of equations.

And as you start to look at them and compare them across each individual equation, you might have noticed that the first one seemed a little off.

And that's because this reaction doesn't actually have the right number of hydrogen or chlorine in the reactants to form all the products.

We don't have enough of what we need in order to make the products that are suggested by this chemical equation.

So that's something we're gonna look at improving next.

Now that we're feeling a little more comfortable about how we can represent chemical reactions, let's look at how we can balance those symbol equations.

Now the main aim when we try to balance a symbol equation is to ensure that we have the same number of atoms of each element on both sides of the reaction arrow so that we have the right number of atoms of elements in our reactants as in our products.

So if we look at a really simple reaction, we have iron plus sulphur makes iron sulphide.

Now the main thing we need to do is to keep our reactants separate from our products.

So underneath that arrow I'm going to draw a line.

And then underneath each of my substances I'm going to draw a representation of it.

So I've got my iron and my sulphur, and then they combine to make one unit of iron sulphide.

I'm also then going to list the element symbols on both sides.

So I have my reactants on one side and my products on the other.

You may wish to simply create it as a table where you list the element symbols once.

I personally like it on both sides of my line that's separating my reactant and products, but it's completely up to you.

You might develop a process that works easier for you.

But when I count up then the atoms I have on each side of my iron, I have one on my reactant side and one on my product side.

And then when I look at my sulphur, I also have one on my reactant side and one on my product side.

So when I then read across those lines, so the iron, I have one each, and my sulphur, I have one each.

In my reactants and products, I could say that this reaction is actually completely balanced as written.

Now that does happen sometimes, in which case the symbol equation is my balanced symbol equation.

But sometimes it doesn't happen.

So what we need to do then is to keep some things in mind when we are balancing a symbol equation that isn't balanced as written simply as a symbol equation.

So a few rules.

The first one is about chemical formula.

It's really important to understand that chemical formula does not change.

If you change it, you are talking about a completely different substance.

And here's an example, okay? If you were to, for instance, change the subscript numbers in the formula, you're actually changing it into a different substance.

So water for instance is H2O.

Let's say you needed another oxygen atom, so you changed it to H2O2.

Well, that is actually known as hydrogen peroxide, that particular formula, H2O, water, you could actually consume that, it's safe for you to drink.

H2O2 is toxic.

So simply by changing, adding that little subscript two behind the oxygen symbol of water to change it into hydrogen peroxide, you've changed something that was completely safe to use into something completely toxic to consume.

So do not change the chemical formula.

Do not touch.

The other thing we need to remember is that coefficients, those big numbers are always found in front of the formula, and they can change.

So for instance, here I have sulphur, sorry, sulfuric acid.

And you can see the green boxes then are at the front.

The numbers are the same size as the capital letters and they can change, okay? And also if there is a number that's not in front of that formula, simply by having the formula there means I have a coefficient of one.

So my formula here of O2 really means I have one O2 molecule.

H2SO4 by itself without a number in front of it really means I have at least one whole unit of H2SO4.

Let's stop here for a quick check.

What numbers can be changed in a chemical equation? Well done if you said B.

The coefficients, those large numbers at the front of formula are the only numbers that can be changed when you are balancing a symbol equation.

Now, besides being careful of remembering which numbers you can and can't change when balancing equation, it's important to remember a few other things, including the fact that all the reactant atoms are reorganising to form the products, and therefore no atoms are being lost or gained during these chemical reactions.

And that the number of the reactant atoms needs to equal the number of the product atoms. So if we go back to that reaction we were talking about earlier, magnesium reacting with oxygen to make magnesium oxide, we know that the formula for magnesium oxide is MgO.

If we leave it at that, with our reactant formula, we can see that there might be this additional oxygen atom that's kind of left over.

And because of that, you might be tempted to add that formula.

And that's not the process that we use here.

The only thing that you can change when balancing equation is those coefficients that we talked about earlier.

All we're doing is changing that ratio of the reactants and products.

So we're not adding anything new suddenly into my reaction mixture.

And I'm not suddenly forming some random extra thing in my products.

I have, I know what I need in order to make my products.

I know what I should be forming.

I can't be adding or taking away from either side.

So the only thing that changes when we balance an equation are those large coefficient numbers at the front of the chemical formula.

Okay, so how do we go about balancing a symbol equation? Now there's gonna be a variety of different ways that you can do it, and I'm going to walk through a very systematic approach that you may find you start skipping steps on the more that you do this.

Balancing symbol equations requires perseverance and practise.

And I know you guys can do this, particularly if you've got a strategy in hand.

So let's go through the strategy I would recommend using.

And the first bit is actually starting with your symbol equation, and then drawing a simple diagram for each substance to keep track of those atoms involved, okay? So like before, I'm gonna draw that line that separates my reactants from my products, 'cause I need to make sure the atoms of each element on each side of that arrow equal each other.

So I'm gonna keep them nice and separate.

Then my diagrams then are going to represent those particles.

So my magnesium exists as one atom.

My oxygen is one particle, but it's a diatomic particle, so I'm gonna have it all in one circle.

But both of those symbols, so each individual atom is actually shown within that one particle diagram.

And then I've got my magnesium oxide.

Now this is a formula unit.

So I have a magnesium ion and an oxygen ion, but it's all one particle unit, which is why I've shown them as the individual ions, magnesium oxide.

But I've put that larger circle around it to make sure that it exists as one unit.

Then I'm going to list my elements in both my reactants and my products, and then I'm going to count up how many I have of each.

So magnesium, I've got one reactant, but two oxygen atoms as a reactant.

And in my products I have one magnesium and one oxygen.

Now it's clear that these are unbalanced, particularly when you compare the oxygen, it's unbalanced.

So I'm gonna have to do something now to balance this equation.

Now I know I can't change the formula for any of the substances involved in my reaction, but using these diagrams, these substance diagrams that we've drawn is gonna come in really handy because the side that you have the fewer atoms of an element on, you're going to add a whole nother diagram containing that atom on that side of the diagram.

So for this one, I can see I have fewer oxygen atoms on my product side, so I'm gonna draw an entirely new substance diagram that contains that element's atom, okay? Now when I do that, I have to recalculate the number of atoms I have of the elements.

So I now have two magnesium atoms and two oxygen atoms. And while my oxygen atoms now are balanced, my magnesium is not, it's still unbalanced.

What you'll need to do then is to continue adding those appropriate substance diagrams where necessary on either the reactants or product side until you have the same number of atoms of each element on each side of that, on each side, the reactants and the product side.

And it's absolutely essential that every time you add one of these substance diagrams that you are recalculating the number of atoms of the elements.

So I can see here from before, I have now more magnesium on my products than I do on my reactants, and therefore I'm gonna add a magnesium substance diagram, recalculate the number of atoms here.

And I can see now that my reaction, excuse me, is completely balanced as written.

So you think about your, pardon me, your reactant equation as being a little bit like a seesaw, and it's tipping one way or the other on that arrow.

Do I have more reactants? Do I have more products? How am I going to eventually get it to balance completely having the right number of atoms of each element on both sides of my equation? So now I know from my work earlier that my reaction is now balanced here, but I need to show that using a balanced symbol equation with my coefficients.

And the way I do that is simply tallying up the substance diagrams that I have drawn.

So I have two magnesium diagrams, one oxygen diagram, and two magnesium oxide diagrams. So I put then those coefficients, remember these are the large numbers the same size as my capital letters in front of my formula, and my balance symbol equation will look like this.

Now you'll notice that the one in front of my O2 in my reactants is gone.

Now this is my balance symbol equation.

You would not be penalised for keeping the one there, but if you remember we said if there's no coefficient in front of that formula, it still represents the number one, okay? Okay, let's have another go at balancing a symbol equation.

We're gonna do it all on one go here.

So I have nitrogen plus hydrogen makes ammonia.

So I'm gonna draw my line underneath the arrow to separate my reactants and products.

And I'm going to draw my substance diagrams. So I've got two nitrogen in one substance, two hydrogens in one particle, and then I have my ammonia in one particle.

And then I'm going to keep track of the number of atoms on each side.

So I have two nitrogen atoms on my reactants and two hydrogen atoms on my reactants.

And in my products I have one nitrogen and three hydrogen.

Now here's a little hint and tip.

Anytime you have atoms that exist by themselves, so my nitrogen or hydrogen, my products, they're not bonded to any other type of atom.

I'm gonna leave those to balance last, okay? So because my nitrogen is unbalanced here, I'm going to put one more ammonia substance diagram on my product side, recalculate my atoms and I have two nitrogens now, which is balanced, but six hydrogens, and my hydrogens now are unbalanced.

So I'm gonna have to add more hydrogen on my reactant side.

And when I do that, I now have four hydrogens and I need more still.

So I'm gonna add one more diagram of hydrogen.

And now I have my balanced atoms, two nitrogens on each side and six hydrogens on each side.

So when I tally up the different substance diagrams that I've drawn, I get my balance symbol equation that looks like this.

N2 as a gas plus 3H2 as a gas makes 2NH3 as a gas.

So I've shown you a diagram here in one way you can do it all in one go.

Now I'm gonna ask you to have a go at trying to balance this symbol equation.

It may take you a little bit of time to get your head wrapped around how to do it.

You may wish to practise it, maybe using a mini whiteboard so you can rub things out really easily or talk it over, work with a partner on this.

But pause the video and come back when you're ready to check your work.

Okay, let's see how you go on.

So first things first, you wanna separate your reactants and products, and then we're going to draw our substance diagrams so we can keep track of the particle units and also look at how many atoms we have of each in each of those particle units.

Keeping track then of the atoms we have in both the reactants and products, I have two nitrogen, four hydrogen, and two oxygen on my reactants, two nitrogen, two hydrogen and one oxygen in my products.

To balance these then, I need to add another water molecule on my product side.

And when I do that and recalculate the number of atoms I have on each side, I now have four hydrogens in my products and two oxygens in my products.

And that balances out this number of atoms in my reactants and my products.

So my final balance of the equation should look like this, N2H4 as a liquid, plus O2 as a gas, makes N2 as a gas, plus 2H2O as a liquid.

Well done if you manage to get that balanced correctly.

Let's stop here for another quick check.

Hydrogen reacts with oxygen to make water.

Now, which particle diagram do you think best represents this reaction? So we have four different examples here and you have a key at the top to help you.

So you may wish to pause the video here and come back to your answers in a moment.

Well done if you said D.

D is the best answer here, because it shows the correct number of atoms necessary for this reaction.

B is an incorrect answer because it's showing the production of hydrogen peroxide rather than water.

A is incorrect because we have the incorrect number of oxygen atoms on the product side.

And C is incorrect because it has the incorrect number of hydrogen atoms on the reactant side.

So in order to balance this in terms of the particle diagrams, D was the best answer 'cause we have the equal numbers of both the oxygen atoms and hydrogen atoms in both the reactants and the products.

Very well done if you manage to get that correct.

Now, I said earlier that drawing the different substance diagrams to help us balance the symbol equation is really useful, but it's also very useful to help us interpret a balanced symbol equation as well.

So for instance, here I have magnesium plus hydrochloric acid makes magnesium chloride and hydrogen.

And what I could do is I could first of all draw a diagram for each of these substances, and then I can use the coefficient to make sure I have the right number of diagrams for each of my substances as well.

And what I can do then is I can double check, do I actually have the right number of atoms of each element in both my reactants and my products.

So let's stop here for a quick check to see on how you can interpret a balanced symbol equation.

So for this one, I'd like you to tell me how many oxygen atoms are there shown in the reactants? Well done if you said D, there are six atoms shown in the reactants.

So the first thing we needed to do was kind of get tunnel vision on our balance symbol equation to the reactants and then focus in on the atoms on the reactant side.

Then what I'm gonna do is draw my three different diagrams to represent each oxygen molecule.

And when I add up all the different atoms that are represented, I get six.

So well done if you manage to get that correct.

Let's try another one.

How many atoms of oxygen are shown in the products? Well done if you said C, there are four oxygen atoms, and this is how we get to that answer.

First of all, you need to have tunnel vision to the product side of our reaction equation.

And we can see that oxygen is found in both of these substances.

So I'm gonna draw my diagrams again, but this time I'm gonna show the oxygens in a different colour just to make them kind of ping out at me and make it easier to count.

Now I've drawn my carbon dioxide and my water, but water has a two in the front of it, so I need to add two diagrams here.

And when I count up all my oxygen atoms, I have four.

So very well done if you manage to get that correct.

Now, you may recall that the coefficients in a balanced symbol equation tell us the ratio of our ingredients, what we're starting with, to how much product we're gonna actually make.

And regardless of these change, the ratio stays exactly the same.

So in my initial balanced symbol equation, I know that I need two magnesium atoms reacting with one oxygen molecule, so half as much, and that will create then two magnesium oxide formula units.

If I was to double this and use four magnesium atoms, I'd need half as much, so this time two oxygen molecules.

And because my coefficients for the magnesium and magnesium oxide are exactly the same, I'd be able to make the same ratio, so four formula units of my magnesium oxide.

Similarly, if I change it to 12 magnesium atoms, I need half as much oxygen, six, and I'd be able to make the same amount of magnesium to magnesium oxide 'cause those coefficients are exactly the same, 12.

We'll come back to look at this later on in your learning, but the key here is that the ratio stays the same.

So if you compare this back to say cooking or baking, let's say you wanted to bake some muffins and the recipe called for two eggs, but you only had one, you could still make those muffins.

You would just have to have all of the other ingredients to keep the ratios the same.

So that's what we're talking with our balance symbol equation.

It's our recipe showing the ratios of our reactants and our products.

Okay, let's move on to the last task of today's lesson.

For the first part, we can see that sulphur reacts with oxygen to make sulphur dioxide using the balanced symbol equation of S plus O2 makes SO2.

What I'd like you to do is to copy and complete the particle diagram to show this reaction.

You may wish to pause the video here and come back when you're ready to check your answer.

Okay, let's see how you got on.

So we can see that for every one sulphur atom, we need one oxygen molecule to make one sulphur dioxide molecule.

And when we look at the balance, sorry, the particle diagram that's been provided, we can see we have nine sulphur atoms, which means we need to have a total of nine oxygen molecules and make nine sulphur dioxide molecules.

And it looks a little bit busy here, and that's because we have gases that are present.

So the molecules are gonna be all over the place, they're bumping into each other and moving all over the place.

So it's organised to show not only the correct number of molecules to show that ratio, but also that we're showing the state symbols here as well.

So very well done if you have the correct number of molecules drawn for your oxygen and sulphur dioxide, and very well done if you manage to represent that in the correct state as well.

Great job guys.

For the second part of this task, I want you to consider this reaction of when propane burns, it reacts with oxygen and it produces carbon dioxide and water.

Now, Andeep has written the chemical equation for this reaction like this, C3H8 plus 4O2 makes 3CO2 plus 4H2O.

What I'd like you to do is to use the reaction equation that Andeep has written to complete the table.

And once you've done that, I want you to consider, is Andeep's chemical equation correct? Why or why not? So I'm looking for a because clause, And if it's incorrect, please correct it.

This is gonna take a little bit of time, so pause the video here and come back when you're ready to check your answers.

Okay, let's see how you got on.

Now, you may have been able to fill the table in a variety of different ways.

You may have simply been able to read the equation and fill in the columns yourself, or you may have drawn out your substance diagrams to help you.

It doesn't matter how you did it, the calculations and how you fill this table in should have been exactly the same.

So we should have three carbon atoms, eight hydrogen atoms, and eight oxygen atoms, all on the reactants side.

And on the product side then, we should have three carbons, eight hydrogens, and 10 oxygens according to Andeep's equation.

You were then asked to decide whether or not Andeep's chemical equation was correct and to explain why or why not.

And to be fair, it is incorrect, and that's because, there's our because clause, the oxygen atoms, when we compare them for the reactants and products are unbalanced.

So we have an unbalanced equation as Andeep has written it.

Now, because it's incorrect, I asked you to please correct it.

And if you have done what you should have done is added another oxygen molecule to the reactants and you'd end up then with a new equation that's balanced and it reads as this, C3H8 plus 5O2 goes to 3CO2 plus 4H2O.

Very well done if you've managed to get that correct.

Okay, for the last part of today's task, I'd like you to consider the reaction of when methane burns in oxygen, it produces carbon dioxide and water.

Now we have four different equations that are written here.

I'd like you to decide which is correct, and for those that are incorrect, why are they incorrect? So pause the video here and come back when you're ready to check your answers.

Okay, let's see how you got on.

So the correct chemical equation for this reaction was reaction B, and then I asked you guys to tell me what was wrong with the other equations.

So A was incorrect because the oxygen atoms are unbalanced.

So even though we have the correct formula for all the substances, there were only two oxygens on the reactants and three on the products.

Don't forget that oxygen atom that's in the water molecule of the products.

C was incorrect because it had the incorrect formula for the products.

It was showing hydrogen gas rather than water, which is H2O.

And D had a similar problem in that it had the incorrect formula for oxygen in the reactants, it was shown as O3, which is ozone, not O2, which is the oxygen gas.

So very well done if you managed to choose the correct chemical equation for the reaction of methane burning in oxygen.

And incredibly well done if you were able to identify even one of the errors in the other reaction equations.

And very well done if you managed to identify all the errors.

I think what we've learned here is that we first have to have the correct formula for all the substances in our equation, and then it needs to be balanced correctly.

Very, very well done today, guys.

Now, we've gone through a lot of work today, so let's take a moment to summarise what we've learned.

While we've reminded ourselves that atoms cannot be created or destroyed during a chemical reaction, all that's happening is that those reactant atoms are rearranging and reorganising to form all the products.

Then we also learned that a balanced symbol equation can represent reactions using chemical formula, and it indicates the ratios of the substances in the reaction.

So it tells me how much of each reactant I need and then how much of each product will be formed.

But a balanced equation tells us more than that.

It also represents the reaction showing us the number of atoms of each element.

And I have an equal number of atoms of each element in both the reactant and the product sides of my equation.

And in order to do that, I need to make sure that when I'm balancing these symbol equations, the chemical formulas are not changed.

Only those coefficients, those large numbers at the front of a formula can actually change.

Now this skill of being able to balance a symbol equation and interpret a symbol equation is something that develops over time.

So be kind to yourself when you are learning to balance equations.

It is a slow process to start and it becomes easier the more practise you do.

So take time, practise a little bit more, it will get easier, I promise.

I've had a great time learning with you guys today.

I hope you did too.

And I hope to see you again soon.

Bye for now.