Lesson video

- Hi everyone.

I'm Miss Barrett from the Oak National Academy, and today we have a very exciting lesson all about chemical reactions.

And this is from the atoms and period table unit.

Make sure you've got a periodic table with you today because that's gonna really help you when we get into some equations later.

Let's get started.

So in today's lesson, we are going to understand the difference between physical and chemical changes, and we're going to have a go at writing word and symbol equations.

Okay, so some key words that are gonna help us in today's lesson.

An element is a substance made from one type of atom.

You might remember this from our first lesson in this unit, a chemical symbol is a one or two letter representation for an element.

Again, this drops from an earlier lesson.

A substance's state is whether it is a solid, liquid or a gas, and you might hear this referred to sometimes as states of matter.

So the outline for today's lesson, firstly we're going to look at physical and chemical changes.

Then we're gonna have a go at some equations.

Then we're gonna have a look at two specific types of chemical reaction, the first one being displacement reactions, and then we're going to look at decomposition reactions.

So let's start with physical and chemical changes.

So a physical change is where matter changes form or state, and here I've got two examples.

So I'm sure everyone's experienced an ice cream melting on their hand.

If something is melting, it is changing state.

Can you remember what state that is from? So that is going from a solid into into a liquid.

So that is changing state.

On the right hand side we have breaking glass, and that's not changing state.

It's still a solid, however, that's changing form.

It's broken into small pieces, but both of those are physical changes.

A chemical change is a reaction that makes new substances.

So here's two examples.

First one, we have iron rusting.

So the rust that forms on the outside of metal, that orangy brown colour, that is a brand new product called iron oxide.

And that forms when the metal is exposed to oxygen and exposed to moisture.

And on the right hand side we have food cooking.

So here we've got a fried egg.

So when you first crack the egg open, it looks very different to how it ends up when you eat it.

So food cooking is a type of chemical change.

Perhaps you can think of some more.

So six signs of a chemical reaction.

The first one is fizzing.

So if you have a solution or a liquid and it is undergoing chemical reaction and it might produce a gas and that might lead to fizzing or bubbling that we can observe in our beaker.

The second is a colour change.

So if there is a colour change, so if something, for example, changes from colourless and it turns blue, that means something brand new has formed and therefore that must be a chemical reaction if we have a temperature change.

So for example, if you mix two solutions together and it increases the temperature, it gets hot, or the opposite, you mix some things together and it gets very, very cold.

This is a sign that there is a chemical reaction taking place.

The fourth one is light is produced.

And I'm gonna show you an example of this in a minute, but this is usually demonstrated by fire.

So if you see a big flash or if you see fire, this means often that there is a huge change in energy and is a sign that a chemical reaction is taken place.

And fifth, if a sound is produced.

So if you hear a popping or if you hear a sort of sizzling or a bang, an explosion, this is all signs that a chemical reaction has taken place.

And then finally, if a smell is produced, so for example, when you are cooking something, if you are cooking your fried egg, you would start to be able to smell the egg and that would smell different to the raw egg.

And again, that shows that something brand new has been produced and is a sign of a chemical reaction.

And for a chemical reaction, it is usually difficult to turn your products back into your reactants.

So the brand new thing that you make, it's very, very difficult to turn that back into what we had at the start.

So for example, again with our fried egg, if you've ever tried to turn your egg back into a raw rag, that's pretty difficult to do.

So usually chemical reactions are what we call irreversible.

So what about our physical changes then when we've talked about our ice cream melting or our glass breaking, are those irreversible? So usually no, usually physical changes are reversible, which means we can turn it back into the thing that it started as.

Okay, so have a go at this.

Which one is the odd one out? So we've got milkshake being mixed, we've got a firework exploding, and then we've got water boiling.

Have a little think which one of those is the odd one out.

So hopefully you figured out that that one was fireworks exploding.

So milkshake mixing is not a chemical reaction, that's just two things mixing together.

There's nothing technically, although milkshake is produced, it's still milk and milkshake syrup is just now mixed as one.

Water boiling is also a physical change.

The thing you are producing, steam, is still water, it's just as a gas.

So that is also a physical change.

A firework exploding is a chemical change that is a chemical reaction that is happening in the sky.

There is light produced, there is sound produced, so there is also a colour produced.

So we know that that one must be a chemical reaction.

So we have two physical changes there and a chemical change.

So we're now gonna think about some examples of chemical reactions and why they are chemical reactions.

So here I've got three stages of a chemical reaction.

We've got a colourless solution in test tube, and we've got a bluey solution in a conical flask.

So that test tube solution is added to the conical flask.

And what do we see happening? So the first thing we see happening is bubbling.

As it's going in we're seeing bubbles or they might even be particles forming, and also there is a flame.

And then in the last step we just have some crystals.

Now is that crystal a solid? Is it a liquid, is it a gas or is it a solution? So yeah, that's right.

The crystals there are a solid.

So that means if we have a look at what we had at the beginning, that looks very different to what we had at the end.

So although that's changing from a solution to a solid, which we might think, well that must be a physical change, there is evidence that chemical reaction has taken place as well.

And that is from our new product produced, which looks different to what we had at the start.

There is a light produced and also there is gas produced from the bubbles.

What about this reaction? So here we've got a strip of metal that's being added to a blue solution.

Over time there are bubbles and then by the end that solution has turned red.

So again, this is a chemical reaction.

Why is that? Well, this is because again, there is a new product formed, there is a gas produced.

We know that because there is bubbles, and there is a colour change.

So there's three things there that prove to us that that must be a chemical reaction.

Overall, what's important to remember is that a chemical reaction is something where there is a brand new product formed.

Okay, so let's test what we've understood so far.

In which two test tubes has a chemical reaction taken place? So have a little look.

We've got A, B, and C.

Think about what the signs are for a chemical reaction and have a think about which ones a chemical reaction is taking place in.

Okay, hopefully that one wasn't too difficult.

We should have worked out that this one was A and B.

Why was that? So if we have a look at A and B, both of them have bubbles that tells us that gas is being produced, that's a new product.

And also B has a little bit of a colour change going on as well.

So that's how, as I said, that one is a chemical reaction as well.

Something to remember though, sometimes we see bubbling when there is not a chemical reaction going on.

So for example, if you have a saucepan of water boiling ready to put your pasta in, that will be bubbling.

That does not mean it's a chemical reaction.

Sometimes we need to look out for other signs of a chemical reaction taking place to know that it is definitely a chemical reaction.

Okay, next check for understanding, true or false, baking a cake is a chemical reaction? Have a little think.

So you might not have realised this before, but baking cake is a chemical reaction, because if we think about it when you've got your cake batter with maybe some chocolate or whatever it is, however you like your cake, we mix that all together and then we put that in the oven.

When we get that cake back out, is it possible to turn that cake back into cake mixture? No, it's not.

So that's one sign that that's a chemical reaction.

And also the product, the cake that we make looks different to what we had at the start.

There is a colour change.

It's usually more brown than when it went in.

And the texture is also quite different as well.

That gives us a sign that is a chemical reaction too.

So to justify the answer, the product is different from what you start with and it is difficult to reverse the reaction.

Okay, next, which of the following is a chemical change? So chemical change, not a physical change.

Have a think.

Is it crushing a bag of crisps? Sherbet fizzing on your tongue or filtering sand and water? All right, so these are common-ish things in life and you've probably done all of these at some point, but you might not realise one of these is a chemical change or a chemical reaction.

And that one is the sherbet fizzing on your tongue.

There are a few things that we can notice there.

One is that your mouth starts to feel very cold.

There is a temperature change due to the chemical reaction that's taking place.

And secondly, it fizzes.

So that must mean there is a gas product being produced.

It's actually carbon dioxide being produced and that is another sign that it is a chemical reaction.

So that's a chemical reaction you can do at home just by buying some sweets from the shop.

Okay, next one.

Which of the following is a physical change? Mixing watercolour paints, lighting a birthday candle and cooking a sausage? Again, all things that you might have done at some point or even seen at some point.

Have a little think.

Okay, so that one is mixing watercolour paints.

So a little bit of a trick there because when you mix watercolour paints, you do produce a brand new colour, but there is no chemical reaction going on there.

All you are doing is combining the pigments of colour to produce a brand new colour, but it's not actually a chemical reaction.

The product is still paint.

There is nothing new made there.

Lighting a birthday candle, that is a chemical reaction.

As I said, if you see fire, chemical reaction going on, burning, and cooking a sausage, that's pretty difficult to reverse.

And the product looks very different to the raw sausage that goes into the oven.

Okay, so onto your first task for this lesson.

Hopefully you've understood the difference between physical and chemical changes so far.

So let's apply that knowledge.

So there are multiple stages to making cookies, for each stage, you are going to identify whether it is a physical or a chemical change that's taking place, and explain how you know.

Have a go on the worksheet, pause the video and come back once you're done.

Okay, welcome back.

Hope that test didn't make you too hungry.

Let's go through the answers.

So stage one, mixing the chocolate chips into the dough.

That one is a physical change.

And the reason is because it would be very easy for us to separate out the chocolate chips from the dough.

There are no new products formed, it's still just dough and chocolate chips, it's just that they are mixed together and it's definitely not a chemical reaction because we didn't see any signs of that.

So we didn't see any fizzing, we didn't see a colour change, we didn't see a temperature change, we didn't hear a sound or we didn't smell anything brand new.

Stage two, separating the dough into balls.

So we start off with a big lump of cookie dough and then we separate out into the smaller balls to put it in the oven.

Is that a chemical or a physical change? That one is also a physical change.

So here again, there's no new products formed.

It's still cookie dough, it's just that it's in smaller pieces and it would be very easy to put it back into a big lump of dough and put it back to what we started with.

And again, there is no signs of a chemical reaction.

Stage three, baking the cookies in the oven.

This one is a chemical change.

And the reason for that is this time there is a new product formed.

This is the baked cookies and it's very difficult to return that back into cookie dough, the raw cookie dough.

So therefore it has to be a brand new product.

And there were a few signs of a chemical reaction here.

There was a colour change, there was a smell produced.

And also when it's cooking you might be able to see some bubbling as well.

So well done if you got those right.

Let's move on to the next part of the lesson.

So the second part of the lesson, we are going to be looking at equations.

So in a chemical reaction, substances known as reactants react together to make new substances called products.

There are chemical reactions happening around us every day, and I'm sure already today you have learned some things that were chemical reactions that you did not realise.

Baking cookies, cooking sausages, frying an egg.

These are happening all the time around us.

So here's an example.

We've got some eggs, flour, sugar, and butter.

If we mix these together, we can turn that into a cake, we can turn that into our product.

So the ingredients we start with are known as reactants.

And the thing that we make is known as a product.

So everyone I'm sure has experienced cooking or seen cooking and therefore you have been doing chemical reactions already.

So equations are a written representation of the process that occurs during a chemical reaction.

So we put on the left hand side, we put our reactants, there might just be one, sometimes two, sometimes more.

So put reactant plus reactant gives us our product.

And there might be just one product, there might be two or there might be more.

So these are called word equations using the substantive names.

So here we've got iron plus sulphur gives us iron sulphide, that is a chemical reaction.

And symbol equations use the chemical symbols that we learned about in a previous lesson.

So this one would be Fe plus S gives us FeS, which is iron sulphide.

So these are word equations on the top and the bottom are symbol equations.

We are gonna learn today how to do these.

So we're first gonna focus on word equations.

So firstly you identify which substances are being used, these are your reactants.

You then identify which substances are being made and these are your products.

And then you put reactants names on the left and product names on the right side of an arrow like this.

So magnesium reacts with oxygen to full magnesium oxide.

And this would be magnesium plus oxygen gives us magnesium oxide.

That's not too difficult, right? Let's have a go.

Fill in the blank in the word equation.

Hydrogen reacts with oxygen to form water.

Write down what you think goes in that gap on the end.

So hopefully you've worked out that hydrogen plus oxygen arrow water.

So all we've gotta do is read the sentence about the chemical reaction, identify which ones are reactants, which ones are products, and put them on the right side of the arrows.

So we're filling in the blank again, carbon, hydrogen, oxygen react together to make ethanol.

What goes in that gap on the end? It is ethanol.

Hopefully you got that one right.

Well done if you did.

Next, aluminium oxide breaks down into aluminium and oxygen.

What goes in the gap? That's right.

If you put aluminium, well done, you've got the answer correct.

So we're gonna look at some symbol equations now, the word equations are the easier part.

This can be a little bit tricky.

So for symbol equations, instead of writing the names of the substances, we use the chemical formulae.

We learn about chemical formulae in the last lesson.

So here we've got 2H2 plus O2 gives us 2H2O.

So the big blue numbers that are written to the left of the substance, these are what we call coefficients and they tell us the number of molecules that are needed in that reaction.

Whereas our little numbers, which are to the right, this is the subscript numbers and these tell to molecule's chemical formula.

So subscript numbers can't change.

So hydrogen, we've got two molecules of H2, of hydrogen, and we've got oxygen, which is O2 and we've got H2O.

So one oxygen atom bonded to two hydrogen atoms, and we've got two of those.

So remember from our chemical formula, we can't change that subscript number.

So H2O is always H2O.

We can't put H202 to try and balance it out, that becomes a different compound altogether.

So we have to keep those little numbers the same.

So some molecules such as hydrogen and oxygen on the previous page, they're what we call diatomic.

And that means they hang around in pairs rather than as single atoms. And it's important that we look out for these when we're balancing equations because this can trip us up.

So hydrogen is H2, oxygen is O2, nitrogen is M2, fluorine, anything group seven floats around in pairs.

So fluorine, chlorine, bromine, iodine, these have all got a little two as well.

So when in a minute when we come onto balancing equations, we have to remember which ones we can't split up.

We've got to keep these in pairs.

So symbol equations have to be balanced, they have to have the same number of atoms of each element on both sides of the equation.

So here we've got calcium, CA, and sulphur, S, makes calcium sulphide, CaS.

So how many atoms of calcium are there on the left and on the right and how many atoms of sulphur? So you can see there that there's just one of each atom.

So that is what we call balanced.

There's one of calcium and sulphur in the reactants and there's one of calcium and sulphur in the product.

So that equation is balanced.

So hydrogen and chlorine, these are both diatomic molecules and hydrogen reacts with chlorine to make hydrogen chloride.

So now let's count how many atoms we've got on each side.

So we've got two hydrogens on the left together and we've got two chlorine atoms bonded together as a molecule.

If we have a look at the product for hydrogen chloride, there is only one hydrogen atom and one chlorine atom.

So that's not balanced.

Somehow we have lost some atoms along the way and that doesn't really make any sense.

So what do you think we have to do to try and balance that? So what we have to do, is put a big two in front of it, because we've got two hygiene atoms and two chlorine atoms. That means we can make two molecules or hydrogen chloride.

So therefore we write a big two in front of the hydrogen chloride molecule.

Okay, next example.

Hydrochloric acid reacts with zinc to produce zinc chloride and hydrogen.

So again, have a little look how many molecules of HCl do I need? Because currently that's not balanced.

Count how many hydrogens you've got on the right and how many you've got on the left, count how many chlorides you've got on the right, how many you've got on the left.

Hopefully you've worked out that you need two molecules of hydrogen chloride to balance that out.

We that means that we now have two hygiene atoms on the left and on the right and two chlorine's on the left and on the right.

The zinc was already balanced.

There was already one of those on the left and one of those on the right.

So that was all good.

Okay, so on the next part I'm going to model how to balance an equation and then we're all going to have a go in the next one together.

So here I've got hydrogen reacting with oxygen to produce water, but this equation, H2 O2 gives H2O isn't balanced.

So I'm gonna show you how we do that.

I'm going to write how many hydrogen atoms I've got on this side because it's H2, there are two.

And then I'm gonna write how many oxygen's I've got on this side.

O2 means I've got two.

On this side, H2O, that means I've got two hydrogens but only one oxygen.

So how do I fix that? Well, I can start by doubling something I need to, you can see that our oxygen's aren't balanced.

So I need to make two oxygen's on this side.

So what I can do is put a big two in front of the H2O to turn this into a two.

However that means I've changed the hydrogens as well and that means I now have four hydrogens on this side.

So now I've upset the balance on the other side.

So I need to make four hydrogens on this side and I do that by putting a big two in front of the H2 and now that equation is balanced.

So there we go.

2 H2O plus O2 gives 2H2O.

So on the next question we've got lithium reacting with chlorine to produce lithium chloride.

So we're gonna use the same technique.

So on this side I've got one lithium and chlorine's, I've got two because of the Cl2.

This side I've got one lithium, so that's balanced, whereas I've only got one chlorine.

So to try and balance that out I can put a big two in front of that one.

That changes this one to a two and this one to a two because I've got two of the whole molecule.

So I just need to go back to this side and put a big two in front of that to make that balanced for all of the atoms. So there we go.

So we've got two Li plus Cl2 gives us 2LCl.

Well done if you got that one.

So magnesium reacts with oxygen to produce magnesium oxide.

If you need to pause the video and work out how many magnesium oxides will be produced.

Okay, how did you get on? So hopefully you realise that there was two magnesium atoms on the left and two oxygen atoms on the right.

So therefore it was possible to make two MgOs.

Well I dunno if you've got that one right 'cause this can be a bit tricky.

Hydrogen reacts with nitrogen to produce ammonia.

So this time we need to balance out the hydrogens on the left, pause the video if you need to.

Okay, so how many molecules of hydrogen do I need? So if we have a look on the left hand side, we've got NH3 and we've got two of those.

So that must mean in total I've got six hydrogen atoms on the right hand side, and on the left hydrogen is diatomic, it floats around in pairs.

So that means we can just divide that six by two and that tells us we need three molecules of hydrogen.

Well done if you've got that one.

So we're gonna move on to task two now.

So this is two parts.

The first part, you're going to write the word equation and add the symbols to the symbol equations.

These are already balanced, you just need to find the symbols from the periodic table.

Pause the video, have a go and come back once you're done.

Welcome back.

Hopefully you didn't find those too difficult.

Let's go through the answers.

So potassium reacts with oxygen to make potassium oxide.

The word equation is potassium plus oxygen gives potassium oxide.

And then the symbol, the only one that was missing there was potassium.

And if you looked on your periodic table, you'd have found potassium is a K.

So that has to go in the gap.

I'll show you the answers to the next ones.

Sodium fluorine makes sodium fluoride, missing symbol was F.

Next one, carbon plus oxygen gives you carbon dioxide and then the symbol of carbon dioxide is CO2.

Remember it's gonna have two O's for the dioxide.

And then calcium plus chlorine gives us calcium chloride.

And the missing symbol here was the calcium, which was Ca.

So for the next task it's similar, but this time you have to try and balance the symbol equations.

All the symbols are there, you just need to put in the numbers to make sure that they balance.

Remember, you can't change little numbers, you can't change the actual formula.

You can only put big numbers in front of the entire molecule or atom.

Pause the video here, have a go and I'll see you when you're back.

All right, so that was a little bit trickier, but hopefully you didn't find that too bad.

So the word equation for the first one, beryllium plus oxygen gives us beryllium oxide.

And if you looked at the formula in the product, the BO, but there was two of them, so we need two Be's, beryllium's on the left hand side.

So we put a big two in front on that one.

I'll show you the rest of the answers.

Hydrogen plus bromine gives you hydrogen bromide.

We needed a two for the Hbr.

Iron plus oxygen gives us iron oxide, here was a little bit more tricky.

We've got 2Fe2O3 and we had to find out how many iron's we needed and there was two Fe's in the iron oxide, but there was two molecules.

So that makes four irons altogether.

And then gallium plus sulphur gives us gallium sulphide.

And this time we had to find the balancing for gallium and sulphur that we needed two gallium's and three sulfurs.

That was pretty tricky.

So a really big well done if you've got any of those right then that is fantastic.

So good job.

So in the last half of our lesson we are going to look at two types of reaction and we're gonna start off with displacement reactions.

So in a displacement reaction, this is when one element takes the place of another in a compound, all displacement reactions follow the same format.

So A plus BC gives us AC plus B.

So if you have a look at this equation, you'll see that the A and the B have swapped places in the product.

So we show you as a particle diagram, got a atom of A and we've got BC molecule and then we end up with an AC molecule and B as an atom or by itself.

So the B and the A have swapped places, and this is what we call a displacement reaction.

So here's an example.

If magnesium is added to copper sulphate, magnesium and copper swap places to make magnesium sulphate and copper.

And we can tell that this has happened because copper sulphate is blue and magnesium sulphate is colourless.

And also the magnesium metal is a grey colour.

Copper is a sort of bronze-y brown colour.

So when magnesium is added to copper sulphate, magnesium displaces copper to make magnesium sulphate and copper.

When magnesium is added to copper sulphate, magnesium displaces copper to make magnesium sulphate and copper.

Write the word equation for this reaction.

So what we need to do if we need to look at that sentence and think about what is it we're starting with and what is it we are finishing with.

So on the left hand side we've got magnesium and copper sulphate.

And on the right hand side our product was magnesium sulphate and copper.

So we're gonna do the next one together.

When zinc is added to lead sulphate, zinc displaces lead to make zinc sulphate and lead.

So have a little think, what would our equation be for that one? What are our reactants and what are the products? So, zinc plus lead sulphate gives us zinc sulphate plus lead.

We see here that the zinc and the lead swap places, zinc has taken the sulphate from the lead.

So in this next example, we are going to be writing the symbol equations.

So a little bit more difficult, but I have helped you out 'cause I've given you the formulas for each of the substances.

So to write the symbol equation here again, we identify what is our reactance and what is our products.

We can see that magnesium copper sulphate are the reactants and magnesium sulphate and copper are the products.

So all we do is put those formulas on the right sides of the equation like this, MG plus Cu SO4 gives us MgSO4 plus Cu, and we can see that that is balanced.

We've got the right number of everything on both sides, so we don't need to put any numbers in front of that.

All right, the next one we're gonna do together.

When zinc is added to lead sulphate, zinc displaces the lead to make zinc sulphate and lead.

Write the symbol equation for this reaction.

Pause the video if you need to.

You might need a few seconds to work this one out.

Okay, so the symbol equation for this one, our reactants were zinc and lead sulphate, so Zn plus PBSO4, gives us Zn SO4 plus Pb.

Well done if you got that one right.

So let's check what we've understood about displacement reactions.

If sodium, NA, is added to silver chloride, AgCl, a displacement reaction occurs.

What are the reactants, what are we starting with? Have a little look at the options.

So we are starting with AgCl and Na.

So these are the reactants.

The next question, same question, but this time, what are the products? What are we going to end with? Think about carefully, what are the things that are gonna swap places? So in this one, the sodium is added to the silver chloride and the sodium and the silver will swap places and will form sodium chloride and silver.

Well I dunno if you got that one because that one was a little bit hard.

Okay, next question.

How can you tell if an equation is displacement? Is it the two reactants are added together to form one product? There are always two reactants and two products or two elements in the reactants will have swap places in the products.

So that one is C.

Two elements in the reactants will swap places in the products.

So when you notice two things, everything's very much the same other than two things have just swapped places, that's when you know there has been a displacement reaction.

Okay, so task three, you're going to complete the word equations for these displacement reactions.

Remembering that displacement just means that things have swapped places.

Pause a video, have a go and come back when you are done.

Okay, let's go through the answers.

So here we were missing part of the name for one of the substances and the reactants.

And if you have a look in the products, the product was lithium chloride and calcium and we started with calcium something and lithium.

So this must have been calcium chloride.

The next one we've got sodium chloride plus fluorine gives us sodium fluoride and? Chlorine.

That makes the equation make sense because we have chloride on the left and now we've got chlorine on the right.

Next one, iron oxide plus aluminium gives us aluminium something and iron.

That must be aluminium oxide.

And then finally silver something plus copper gives us copper nitrate and silver.

Well that must have been silver nitrate plus copper.

Okay, so your next part of the task, you're going to write a word equation and complete the symbol equation for this reaction.

So when zinc, Zn, is added to copper nitrate, CuNO32, don't let that formula put you off, that brackets just means there's two of the NO3's attached to the copper, zinc displaces lead to make zinc nitrate, ZnO32 and copper, Cu.

Write the word equation for this reaction and then complete the symbol equation.

Pause the video and come back once you have completed it.

Okay, so hopefully you didn't find the word equation too hard.

The word equation was zinc plus copper nitrate gives you zinc nitrate and copper.

Symbol equation.

So we just need to look at those formulas and add those into the right places.

Zn plus Cu NO32 gives us Zn NO32 plus Cu.

They are a little bit tricky.

So really good job if you've got any of those rights.

So we're gonna move on to the last part of our lesson today, which is about another type of chemical reaction called a decomposition reaction.

So a decomposition reaction is when a substance breaks down into two or more smaller components, all decomposition reactions follow the same format.

So here we've got AB as a molecule and that breaks down into A and B.

So here's our particle diagram.

You can see the A and B were bonded at the start and now they are two separate atoms. So this is the format of a decomposition reaction.

So here's an example.

When heated sodium hydrogen carbonate breaks down into sodium carbonate and water and carbon dioxide.

So sodium hydrogen carbonate you might have heard of as baking soda.

And we sometimes add that into our cakes and other bakes and it causes cakes to rise when they are baking.

So if we have a look at what is happening during that reaction, why do you think the cake is rising? So the sodium hydrogen carbonate breaks down into sodium carbonate water and importantly carbon dioxide.

So the carbon dioxide is a gas.

So what's happening is that carbon dioxide's being produced and bubbling through the cake mixture causing air pockets and causing that cake to rise.

So that is an example of a decomposition reaction.

Another example, when heated, copper carbonate breaks down into copper oxide and carbon dioxide, and here we've got a picture of the reaction.

So copper carbonate is green, that's being heated in test tube, and that turns into copper oxide, which is a black powder and carbon dioxide, which is a gas.

This is a decomposition reaction.

So what I want you to do is again, write the word equation and the symbol equation for this decomposition reaction that we just talked about, the decomposition of copper carbonate.

If you need to pause the video and have a go.

Okay, so our word equation for this reaction is copper carbonate gives us copper oxide plus carbon dioxide.

And then our symbol equation is CuCO3, gives CuO plus CO2.

Well done if you've got those right.

When heated magnesium carbonate breaks down into magnesium oxide and which other product? Think very carefully about our previous example.

Is it H2, hydrogen, O2, oxygen, or CO2, carbon dioxide? Hopefully you remember this example.

This was carbon dioxide.

Bit of a clue in the name, magnesium carbonate, that will give you carbon dioxide and this is one of a very common product in a decomposition reaction.

How many reactants are there in decomposition? In a decomposition reaction, there is only one reactant.

So what we're usually doing is we are, sometimes it can happen on its own, but usually we are heating something up to break it down.

So there's only one reactant there.

Right, so we are onto the final task for this lesson.

So here you're going to complete the equations for the decomposition reaction.

So read the equations and think about what goes in that gap.

Pause the video, have a go and I'll see you when you get back.

Okay, how did you get on? Let's go through the answers.

So the first one, beryllium carbonate gives us something oxide and carbon dioxide.

The missing thing there must be beryllium.

The next one, calcium carbonate gives us calcium oxide and something.

Remember what is often the product in a decomposition reaction, that is carbon dioxide.

The next one missing gap was iron.

And this time we had some symbol equations.

So if we have a look here, this one was chlorine, the Cl2, and the missing symbol in the last one was Fe from the iron oxide.

So in the next part of this task, you are gonna identify if the equations are displacement or decomposition.

Remember, displacement is when things swap places.

Decomposition is where something breaks down into two or more smaller parts, have a go, pause the video.

Good luck.

Okay, so hopefully my clues helped you out a little bit there and it wasn't too tricky.

So the first one, calcium bromide plus lithium gives us lithium bromide plus calcium.

Clearly there is something that the metals have swap places there.

So that one is a displacement reaction.

The next one, zinc carbonate produces zinc oxide and carbon dioxide.

That's one thing breaking down into two smaller things, that's decomposition.

The next one's the same, decomposition, and then the final one is a displacement.

So the next part, the final part, this is the same idea, but this time I've given you the symbol equation.

So it's a little bit more difficult.

But take your time, pause the video, have a go, and I'll see you when you're back.

Okay, let's go through the answers.

Don't worry if you found those tricky, they are supposed to be difficult, so don't worry if you found those hard.

Just check your answers now.

So the first one, 2AgBr gives 2Ag plus Br2.

That one was decomposition.

There's one thing on the left on the reactant side, it's broken down into two small pieces.

The next one we can see that the Ag and the K have swapped places, so that must be displacement.

The next one we can see the calcium, Ca, and strontium, Sr, have swap places.

So that is also a displacement.

And the next one, we've got H202 breaking down into two smaller products.

So that one must be decomposition.

Well give yourself a huge pat on the back because you've done so, so well.

There's been so much new information today and loads of tasks to get on with.

So be really proud of yourself that you've made it to the end.

Really, really good job.

So to summarise, changes to substances can be physical or chemical.

When matter changes, but it's still the same substance, this is a physical change.

Chemical reactions create new products.

Chemical equations can be written as words or symbols.

Symbol equations have to balance.

This means they have the same number of atoms of each element on both sides.

When a substance breaks down into two or more smaller substances, this is decomposition and displacement reactions occur when an element takes the place of another in a compound.

Have a go at the exit quiz and see how much you've learned today.

And a really, really, really big well done, because like I said, that was a lot to get through today.

Hopefully I will see you next time.

Thank you for using the Oak National Academy.