Hello, my name's Mrs. Navin, and today we're going to be talking about three types of chemical reactions as part of our unit on calculations involving masses.

Now, you may have some experience of the reactions that we talk about in today's lesson from your previous learning, but what we do in today's lesson will help us to not only answer that big question of what are substances made of, but it'll help us to better interpret the representations of a chemical reaction in the language of chemistry.

And this will definitely help us in our study of chemistry as we move forward.

So let's get started.

So by the end of today's lesson, you should hopefully feel more confident to using chemical equations to both identify and describe oxidation, decomposition and precipitation reactions.

Throughout the lesson, I'll be using some keywords and these include chemical equation, oxidation, decomposition, and precipitation.

Now the definitions for these keywords are given in sentence form on the next slide, and you may wish to pause the video here so that you can jot down a quick description of each for reference later on in this lesson or later on in your learning.

So today's lesson is broken into two parts.

We'll start by looking at chemical equations in general and then we'll move on to look more closely at some common reactions.

But let's get started by talking about chemical equations.

Now chemical reactions are all represented by chemical equations.

And all chemical equations follow the same order.

You have your reactants, which is what your starting substances are on one side, and then you have an arrow showing the products.

And the products then are essentially what substances are being formed.

So the reactants are what react, and they're always on the left-hand side of this arrow.

And the products then are what are produced and they're always on the right-hand side of the arrow.

And notice that we're always using an arrow in our chemical equation, not an equal sign like you might be tempted if you were talking about a mathematical equation.

So let's look at example here.

I have some pictures representing reactants and products, and my reactants are these two substances on the left, and my product then is this one on the right.

So once I have my arrow in place separating my reactants and products, the thing I need to do now is go back and name those reactants.

So my reactants here that I have are magnesium and oxygen, and my product that's been formed then is magnesium oxide.

So this final equation here of magnesium plus oxygen arrow, magnesium oxide is what is known as my chemical equation.

And then chemists might read it like this, magnesium add oxygen changes into or forms magnesium oxide.

And so what we've done here is simply use the names for our reactants and products.

And then anytime we have a symbol in that equation, that's where you can add your word.

So the addition sign is using add or reacts with, and the arrow then simply is read as changes into, forms or produces.

So it's telling us that that change between my reactants and my products from within my chemical equation.

Let's stop to see how you guys have been listening.

Which of the following is the correct way to represent a chemical reaction? Well done if you said D.

The reactants are on the left-hand side of the arrow and the product's then on the right-hand side of the arrow.

You may have been tempted by option B, but that used an equal sign, which is what you use in maths, and it is not used in chemical equations.

The well done if you managed to choose D.

Great start guys.

Let's try another one.

Which of the following is the correct chemical equation for the reaction that is shown? Well done if you chose C.

We have our chlorine and the sodium, which are my reactants, and they're on the left-hand side of my arrow.

And then the sodium chloride, which my product is what is on the right-hand side of my arrow.

Now you'll notice that in C, although the chlorine is listed first in my chemical equation and in my pictures it's written second, it doesn't matter what order my reactants or products are listed in my chemical equation as long as they're on the correct side of the arrow.

So well done if you managed to choose C.

Now, some chemical equations go a little bit further and describe reactions using chemical formulae rather than their chemical names.

Now these equations then can indicate not only the chemicals that are involved but also give an indication of what elements are present in those chemicals as well.

So if we go back to this example from earlier, we had our word equation using the chemical names of the substances.

So magnesium plus oxygen makes magnesium oxide, but if we were to change that to formula then, we'd have Mg, O2 and MgO to represent those substances.

Now if a chemical equation is using formula to represent a reaction that's taken place, it must also indicate the ratio of the reactants required and the products that are produced.

So these equations are often referred to then as a symbol equation and they need to be balanced, which we can look at at a later time.

But if we look at our symbol equation here and try to show this idea of ratios, we can see that there are numbers in front of the formula.

And that number then indicates the ratio of what is needed and what is gonna be made.

So the two in front of my Mg means that I have two magnesium particles.

If there's no number in front of our formula, essentially means I have one.

So I have one particle of my oxygen.

And then again with the two in front of my MgO, it means I have two particles of magnesium oxide that are gonna be produced.

Now if an equation again is using formula and we have that balanced symbol equation, you will also regularly find state symbols included and a state symbol indicates the physical state of all the substances in that reaction.

And the state symbols you come across will be a lowercase G in brackets for gas, a lowercase L for a liquid, a lowercase S for solid, and then you'll also find a lowercase AQ, which means aqueous.

And that simply means that that substance has been dissolved in water and these state symbols then are included next to the chemical formula in a subscript manner.

So if we again go back to that equation we were looking at earlier, we have our balance symbol equation and my magnesium we can see from the picture is in the solid state.

So next to the Mg, I'm going to put a lowercase S in brackets behind the formula, my gas of oxygen will have a G then, and then I can see that the MgO looks like a powder and therefore it's going to have the subscript S representing a solid.

Let's stop here for another quick check.

True or false, chemical equations are only written using chemical names.

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

Chemical equations can be written using both the chemical names in a word equation or the chemical formulae in a symbol equation.

Well done if you managed to get that correct, you guys are doing really well, keep it up.

Okay, it's time for the first task of today's lesson and what I'd like you to do is to match up each key term to the correct description.

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

Okay, let's see how you got on.

Now, I think there might have been the temptation to argue a point that some of these key terms could be matched up to a few different descriptions.

What we're really looking for here is the best description and what I'm thinking about specifically is this keyword of chemical equation.

It probably could have been matched to multiple descriptions, but the best one here is reactants arrow products.

And that's because a chemical equation is a generic hold all, any chemical reaction will always have the reactants on the left-hand side of the arrow and the products on the right-hand side of the arrow.

A word equation then the best matched here is an example which is potassium plus sulphur arrow, potassium sulphide.

A symbol equation then is going to be one that uses chemical formula to represent that reaction.

And so the best description is the top one where we have Mg plus Cl2 arrow MgCl2.

And a state symbol then is something that has letters within brackets that could be subscript.

And so my state symbol is the AQ in brackets.

Well done if you managed to get all those correct.

Okay, for the next part of this task, what I'd like you to do is to take each sentence that describes a chemical reaction and change it into a word equation.

And I'd like you to do this in a very systematic process.

So the first thing you want to do is to draw a circle around each reactant that you find in the sentence and a square around each product that you find in that sentence.

Then use that as a guide to write a word equation for each of those reactions.

This may take a little bit of time and you may wish to use a different coloured pen or pencil for your circles and your squares, or if you wish to highlight instead, that's absolutely fine, but pause the video and come back then when you're ready to check your answers.

Okay, let's see how you got on.

So for part A, we had hydrogen reacts with oxygen to form water.

So my reactants here are going to be hydrogen and oxygen because they're near to that word reacts with.

And then water is gonna be my product because it's what's being formed.

Using that, and my generic guide of a chemical equation is products on one side and reactants on the other, then my word equation should read hydrogen, add oxygen, arrow water.

For B then my reactant was calcium carbonate and my products were calcium oxide and carbon dioxide.

So the word equation is calcium carbonate arrow, calcium oxide plus carbon dioxide.

Now remember, you could have those products in either order as long as they are on the right-hand side of the arrow.

For C then, my reactants were going to be iron and copper sulphate.

And my products were provided first in this sentence and that is iron sulphate and copper.

So putting that into my word equation, I have iron plus copper sulphate, arrow, iron sulphate plus copper.

Now remember, these can be in either order as long as they're on the correct side of the arrow.

So well done guys on having a go at changing our sentences into chemical equations.

So for the next part of this task, what I'd like you to do is to convert the word equations from part two into symbol equations and to include state symbols in those symbol equations.

Now at this point I would recommend that you get a periodic table handy, so you are using the correct element symbols and also I've provided a little bit of extra information for some of those substances that you may be less familiar with.

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

Okay, let's see how you guys got on.

So the first equation we had was iron plus sulphur, arrow iron sulphide, and we need to change that into a symbol equation with state symbols.

So if you've done it correctly, it should look like this.

Fe in the solid state plus S in the solid state, arrow, FeS in the solid state.

Now it's really important when you're writing these that the first letter in any element symbol is capitalised and the second letter is lowercase.

It may seem really nitpicky or something weird to go on about, but it is actually very important that we are representing these chemicals correctly.

So do take the time to be careful in your writing.

For the second equation then we should have CaCO3 in the solid state, arrow, CaO as a solid plus CO2 as a gas.

Now again, the CaO as a solid and the CO2 as a gas can go in either order as long as you have the correct formula and the correct state symbol attached to that formula and that both of those are on the correct right-hand side of the arrow at this point.

For C then, we've got iron plus copper sulphate makes iron sulphate plus copper.

So the symbols then should be Fe as a solid plus CuSO4 aqueous because it's dissolved in a liquid, in dissolved in water, arrow, FeSO4, aqueous, AQ, plus Cu as a solid.

Now very well done if you've managed to get the correct formula and incredibly well done if you are also able to include those state symbol guys, really, really well done.

Now that we're feeling a little more confident talking about chemical equations, let's look at some common reactions.

Now there are several different types of chemical reactions, but what I'd like to do in today's lesson is to look a little more closely at three specific types, and these include oxidation, decomposition, and precipitation reactions.

Now, features of each type of these reactions can actually be found within a chemical equation.

And in fact, chemists can glean information from a chemical reaction without even seeing it happen to help them to deduce and classify what type of reaction has actually taken place.

Now, oxidation reactions are those in which oxygen bonds to elements of the reactants, and we can see an example here where we're burning magnesium in air, so it's reacting with oxygen in a crucible, okay? Now many oxidation actually form oxide products.

So if we go back to that example of magnesium burning in air, we can see that it can be represented in our word equation of magnesium plus oxygen makes magnesium oxide or in its symbol equation just below.

But the features within this chemical equation can help us to classify this as oxidation because the oxygen has bonded.

So we have oxygen as a reactant in our chemical equation.

And because most oxidation reactions form an oxide product, if we have an oxide product in addition to oxygen as a reactant, then more than likely we have an oxidation reaction that has taken place.

Now, oxidation reactions are really common in everyday life.

For instance, they're one of the reasons why fruit sometimes will change colour or brown once it's been cut.

But another really common example is combustion.

Now combustion is simply an oxidation reaction in which heat energy is released.

So whenever you are burning some wood or coal, something like that, you have a combustion reaction taking place.

For coal in particular, if we were to write that as a chemical equation, would be carbon plus oxygen makes carbon dioxide, and we have those clues within our chemical equation to classify this as oxidation.

We have plus oxygen as our reactant and we have an oxide dioxide, but an oxide product that's been formed.

Now during combustion, each element in a substance will join with oxygen to produce a different oxide product.

So looking at another example, here we're going to burn methane for instance, in a Bunsen burner, the word and symbol equations would look like this.

Now the first thing I can see that indicates this might be an oxidation reaction is that I have plus oxygen in my reactants.

Now the chemical formula for methane is CH4.

So I have a carbon and hydrogen.

So if I follow the carbon from my reactants to my products, I can see that carbon dioxide has been formed.

And the hydrogen from the methane then has also joined with oxygen this time to make water, also known as dihydrogen oxide.

So what I have here now are two oxide products that have been formed, two pieces of evidence to show that this combustion reaction is actually an oxidation reaction.

Another example of an oxidation reaction that takes place in everyday life is the corrosion of metals.

And we have here an example of corroding iron.

Now, if I write out the word and symbol equation for this reaction, they look a little complicated at first glance, but if we take a closer look, we can see that it includes plus oxygen in the reactants, and my product is hydrated iron oxide.

We know this by another name, it's rust.

But ultimately we have two clues in our chemical equation that indicate corrosion is an oxidation reaction.

Let's stop here for a quick check.

Combustion reactions always form one oxide product, true or false? Well done if you said false, but which of these statements best supports that answer? Well done if you said A.

Each element in a reactant will bond with oxygen individually to form an oxide product in a combustion reaction.

Well done.

Let's try another one.

Which of the following equations describes an oxidation reaction? Well done if you chose C.

We have both pieces of evidence needed here for an oxidation reaction plus oxygen in the reactants and an oxide in my products.

You may have been tempted by A, because it has oxygen in the reactants, but it's forming a chloride product and that doesn't fit.

Also, if you're forming sodium chloride, you need chlorine in the reactants, and we don't have that here, so this reaction probably wouldn't even happen.

And then for B, we do have an oxide and a oxygen that is added to it, but they're on the wrong sides.

Dihydrogen monoxide is actually water and it's the reactant.

If this was gonna be an oxidation reaction, we need to have the oxide in our product side of the equation, and that's not present here.

So well done if you chose C.

Now you may be familiar with this picture.

It's a compost pile.

Sometimes they're open to the air and sometimes they're black bins at the back of a garden.

But ultimately what's happened is that people tend to put food waste or garden waste into it to help those substances to decompose or to break down.

So a decomposition reaction then is a reaction in which the reactant compound will break down into two or more products.

And chemical equations then can indicate a decomposition reaction because it tends to have one reactant and multiple products.

Now, limestone contains a mineral called calcium carbonate.

And when calcium carbonate is heated, it breaks down into calcium oxide and carbon dioxide.

And if I was to write out the word equation, this is what it would look like and we can see clearly that I have one reactant and multiple products form.

So this is a good example of a decomposition reaction.

What's interesting about decomposition reactions is that they're usually triggered by the application of energy and that energy source then that triggers the reaction to start is included in the chemical equation, but we put that energy source over the arrow.

So if we go back to that decomposition of calcium carbonate, we would have the chemicals are the only things listed on either side of the arrow and the source of energy then is placed above it.

And for this particular decomposition reaction, the energy is heat.

Some substances could actually undergo decomposition when electricity is applied.

And this is an example here.

If we were to take water and apply electricity to it, it would produce then hydrogen and oxygen.

So again, we'd write our word in simple equations as such, and then the energy source of electricity is placed over the arrow.

Still other substances could undergo a decomposition reaction when light is present, and this tends to be why you find them in dark brown bottles.

This particular chemical of hydrogen peroxide will undergo decomposition in the presence of light and form water and oxygen.

So again, we have our word and symbol equations that are listed here, and then the source of energy of light is placed over the arrow.

Let's stop here for a quick check.

True or false, reactants undergo decomposition only when heat is applied.

Well done if you said false, but which of these statements best supports that answer? Well done if you said A, decomposition can be triggered by electricity or light as well as heat.

Well done for getting that correct.

In precipitation reactions, what we tend to have then are two solutions, and here they're colourless, that react together to form an insoluble salt.

And in this particular reaction, we had potassium iodide and lead nitrate reacting to form lead iodide and potassium nitrate.

And we know a reaction's taken place from that colour change.

In a precipitation reaction the easiest way to identify it in a chemical equation is by looking at the state symbols that are involved.

So if we remind ourselves a precipitation reaction then, are two solutions reacting together to form that insoluble salt.

So this reaction we saw earlier of potassium iodide and lead nitrate making lead iodide and potassium nitrate.

Here, it's more useful to look at the symbol equation because that's the one that includes those state symbols.

So solutions then, if you remember, are shown using that state symbol of AQ of something that's been dissolved in water.

And if we're forming an insoluble salt, then what we're doing is forming a solid.

So here looking at those state symbols is particularly useful to identify if a precipitation reaction has taken place.

Let's stop here for a quick check.

Which chemical equation correctly represents a precipitation reaction? Well done if you chose C.

You may have been tempted by A, because it includes two aqueous solution state symbols and a solid, but one is a reactant and one is a product.

What we're looking for are those two aqueous solution state symbols on the reactant side and then one solid that's being formed in a product side.

The other thing we need to double check is that the solid is in fact a salt because it's an insoluble salt.

So we're looking at the formula involved for that solid to double check that it is formed from a metal and a non-metal.

So very well done if you chose C.

Okay, let's move on to the next tasks in today's lesson.

So for this first part, what I'd like you to do is to match the type of reaction to the correct description.

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 oxidation reactions are those that bond with oxygen.

So the best description is the bottom description.

Decomposition reactions, if we remember decompose means to break down and therefore decomposition's best description is the top one.

And a precipitation reaction then is when an insoluble salt forms from two solutions and that insoluble salt then falls out or precipitates out of the solution.

So well done if you match those up correctly.

Now, I said earlier that there are features within chemical equations that can help us to identify what type of reaction has taken place.

So what I'd like you to do here is to read through the features that have been suggested and put them into the correct column that matches that type of reaction.

So you may wish to discuss these ideas with the people nearest you, and I'd recommend that you pause the video and come back when you're ready to check your answers.

Okay, let's see how you got on.

So for oxidation, I would've said that we are looking for reactants that include plus oxygen or plus O2 as a gas.

You could also say that it can produce oxide products as well.

In a decomposition reaction I'm looking for one reactant on then two or more products that are being formed.

I would also look for an energy source that is applied being described over the arrow of that chemical equation.

And for precipitation reactions, I'm gonna focus in on those state symbols where I have two aqueous solution reactants and a solid product that's being formed.

Well done if you manage to get even one of those descriptions under each column and well done if you manage to match them all correctly.

For the next part of this task, what I'd like you to do is to label each chemical equation as representing either an oxidation, decomposition, or precipitation reaction, and you may wish to refer back to the last two parts of this task to help you if you're not sure.

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 reaction A is an oxidation reaction because I have plus O2 and I have an oxide product that's formed.

B is a decomposition reaction.

I'm starting with one reactant and I have multiple products.

C is a precipitation reaction.

Again, I have those two aqueous solutions and forming an insoluble solid salt.

D is an oxidation reaction.

I have plus oxygen as my reactant, I've formed a dioxide product and if we remember, water is also known as dihydrogen oxide.

So it's an oxidation reaction.

E is going to be a decomposition reaction because I have one reactant and multiple products.

F is a precipitation reaction.

Again, I have those two aqueous solutions and a solid salt that's being formed and it's insoluble.

Very well done if you managed to get those correct.

Good job guys.

What I might recommend doing if you haven't already done so, is to maybe go back with a highlighter and highlight the parts of those equations that you looked at that were helping to indicate what type of reaction they were representing here.

It might help you when you come back to look at your work later on if you use them for revising.

Okay, last part of today's tasks.

Jun and Sofia are discussing which way is best to represent a chemical reaction.

And what I want you to do is decide who do you agree with the most and why.

So Jun says that word equations are the most useful because you don't need to know the chemical symbols to know what's going on.

Sofia reckons that a symbol equation is better because you can see both what elements a substance is made from and the state it's in during the reaction.

Now I'd like you to decide who you agree with most, but crucially, what I'm looking for is that because clause.

Why have you chosen that particular person's choice on representing a chemical reaction? So pause the video here, maybe have a discussion yourself and come back when you're ready to check your choices.

Okay, let's see how you got on.

Now, before I go through my answer, I just want to point out that when you get a question like this that says who do you agree with the most and why, we're not really looking at your answer of who you've chosen.

The crucial part of your answer is that because clause, why have you chosen that particular? How have you supported your choice? So I'm not really interested in who you've chosen with.

I'm interested in how you have supported your decision, okay? So, I reckon that both Jun and Sofia are correct.

However, I would argue that using a symbol equation helps to communicate more efficiently in the language of chemistry using those symbol equations, okay? And it's providing more information even about that reaction because a symbol equation is using those chemical formulae and it's telling me then the elements that are involved in those reactants and products.

It also includes state symbols.

So it's telling me the state of that substance in the reaction.

A symbol equation is also really useful when it's balanced because it's showing me the ratio of the reactants to products that are involved.

So whilst both of them are correct, I would say that you probably get more information out of a symbol equation and that's why I would argue that it's probably a more useful one to be using when you are representing a chemical reaction.

That was a tricky one.

I hope that you guys had a good discussion about this, but remember what's crucial here.

It's not who you've chosen, but why.

So well done on a tricky final task.

Now, we've done a lot in today's lesson, so let's take a moment to summarise what we've learned.

Well, we reminded ourselves that a chemical equation can tell us about the reactants in products, but we remember that the plus symbol is read as and, or reacts with, and the arrow symbol is read as changes into or forms. We also remind ourselves that state symbols are used in symbol equations and they can indicate if the substance is in the solid, liquid or gas states, or if that particular substance has been dissolved in water and is in therefore an aqueous solution.

We also learned about three types of chemical reactions, one of which was oxidation reactions.

And in these ones, a reactant is combining with oxygen and often forming an oxide product.

Decomposition reactions then are those in which a reactant compound breaks down into two or more new substances.

And a precipitation reaction then is one in which two aqueous solutions have come together to form an insoluble salt that precipitates or falls out of that solution just like precipitation falls out of the sky.

I had a really good time learning with you guys today.

I hope you enjoyed learning with me, and I hope to see you again soon.

Bye for now.