Welcome to today's lesson called the Characteristics of Chemical Reactions, which is part of the unit called Understanding Chemical Reactions.

Now, what we're going to look at today is what a chemical reaction is and what it isn't, and we're also going to look at what physical changes are and what chemical changes are.

So my name's Mrs. Clegg.

Let's get learning.

Here are the outcomes for today's lesson.

So by the end of it, we should be much more confident in being able to describe some of the changes that indicate a chemical reaction has taken place.

And here are some of the key words for today's lesson.

So, chemical reaction, irreversible reaction, the reactants, and product.

So those are the words I'd like you to watch out for today, and here we've written them into a sentence.

So you might want to take some notes so that you can refer back to them during the lesson.

I've split up today's lesson into two parts.

So the first part, we're gonna look at those characteristics of chemical reactions and work out what one is and isn't.

And then we're gonna look at the physical and chemical changes that occur.

So let's get started with the first part of our lesson.

So physical changes have some key features.

Two things to to remember.

They can be reversed and no new substances formed.

So if we look at the picture there, we've got an image of solid silver, and we can melt it with high temperatures to produce molten silver there.

And then that molten silver, we could freeze it and we get back to solid silver.

So the change has been reversed and no new substances have been made at all.

We've got silver all the way through.

So let's look at a couple more.

So a wax candle, when it's heated, when the wax is heated, it melts, it becomes liquid, and then it will freeze and go back to being solid when it cools.

So it's not a chemical reaction because we've made no new products, but we have seen a change of state happen.

Water, we can boil it in our kettle and form steam, and then we can condense it back to liquid when we cool it.

So again, not a chemical reaction because no new products are being made.

A change of state has occurred.

Let's have a quick check.

So which these statements are true about physical changes.

Well done if you said a physical change can be reversed, but also a physical change produces no new substances, so fantastic if you've got both of those.

When a chemical reaction takes place, new products are made, and you can observe changes occurring.

And these changes might include things like colour changes, bubbling, changes in temperature, an odour or a smell being given off, emission of light, sound, and precipitation when a solid is formed from solutions.

So the sparkler here, that is definitely a chemical reaction because we can see changes in colour.

We definitely see a change in temperature.

The wire gets very hot, doesn't it? There's often a smell associated with the reaction of the sparkler.

Light is given out and often a sound, sort crackling sound.

Here's some more chemical reactions taking place.

Let's have a look at these.

So watch this one again.

So we've got colourless solutions.

When they're mixed, we get a change of colour, and precipitation occurring, and that shows that a new product has been made.

And here's another one.

So we've dropped a tablet there in, and you can see fizzing occur.

And so bubbles are being made.

And in science, we call bubbling and fizzing effervescence.

So we can see the bubbles being made, and that shows that a new gas has been produced.

So therefore there's been a new product made.

If you add iron filings to copper sulphate solution and measure the temperature, you'll see that actually you get a temperature increase.

So that also tells us a chemical reaction has taken place.

And you might have had glow sticks, and a chemical reaction is taking place in those to produce the glow when you break the stick.

When the chemicals react together, you get this glowing when they're emitting light.

So that's a chemical reaction occurring.

So let's have a quick check.

You can have more than one correct answer here.

So when a chemical reaction takes place, what might you observe? You might observe a colour change, a temperature change, or a precipitate being formed, or lots of them together.

Well done if you've got all of those.

Brilliant.

When a chemical reaction takes place, it's generally irreversible.

We can't go back to the original reactants and the atoms involved are rearranged to join or bond to different atoms and new products are made.

So I'm gonna show you here.

So if we've got the chemical reaction of methane reacting with oxygen, carbon dioxide and water are formed.

And let's just have a look at the atoms. So methane is made from carbon, that's the C, and hydrogen H.

You can see there's one carbon and four hydrogen atoms there in methane.

Oxygen.

We've got two molecules of oxygen involved there, and then we produce carbon dioxide where the oxygen is now bonded to carbon.

And water, where oxygen's now bonded to hydrogen.

You can see that we've got exactly the same number of atoms, but they're all changed around.

So we've got new products.

That's what happens in a chemical reaction.

Let's have a quick check.

So a chemical reaction has occurred.

What happened to the atoms in the reactants? Have a look at the statements and see which one you would choose.

Well done if you said C, the atoms have rearranged and joined or bonded to different atoms. Good.

If they stayed joined or bonded to the same atoms, nothing would've changed, and atoms cannot be destroyed.

Another question, all chemical reactions are reversible.

Is that true or is that false? Well done if you said false.

And can you now say why you thought that? So which of these two statements helps you? Well done if you said A, that atoms are rearranged to form products.

Another check.

When magnesium metal reacts with acid, it bubbles and the temperature increases.

This is not a chemical reaction.

Is that true or is that false? Well done if you said false.

And which of these statements helps us to explain why it's false? Read both statements before you make a judgement.

Well done if you said A, the bubbling or effervescence shows that a new product of a gas has been made.

Let's have a quick summary.

So for a chemical reaction, when changes take place, atoms are rearranged.

We get new products made, it's generally irreversible, and it involves a chemical change.

If we're looking at physical change, then atoms are not rearranged.

We get no new products.

The change is reversible, and it usually involves a change of state, from solid to liquid, or liquid to gas, or gas to liquid, et cetera.

So which of these images involves a chemical reaction? Which one do you think? Well done if you said C.

Here's another question for you.

Select the option to complete the sentence.

Physical changes can.

So what would go well with the end of that sentence? Well done If you said B.

Physical changes can be reversed.

No new substances are formed.

We're going to do a task now.

So here's a list of changes.

I want you to decide whether each change is a physical change or a chemical change.

And I want you to put your answers in a table like this.

So have two headings and then put the changes in the right column.

Pause the video and rejoin us when you've done it.

So let's have a quick look at the answers and see how you've got on.

So in our table, wood burning, nail rusting, milk turning sour, and meat cooking in an oven should all be under the chemical reaction.

Heading and physical change, we've got wax melting, water boiling, the perfume evaporating, and salt being added to a soup, and sugar added to tea.

So another question now.

I'm going to give you a whole load of observations and I want you to put them under the correct column in the table.

So we've got no smell and smell, bubbling, no bubbling, temperature increase, temperature decrease, or no change in temperature, precipitation produced, no precipitation produced, colour change or no change in colour.

So have a go at that, pause the video and rejoin us when you're finished.

Let's have a look at the answers.

So in our table, smell would go under chemical reaction, and physical change, no smell.

Bubbling is a chemical reaction.

Temperature increase or temperature decrease could be chemical reaction, whereas no change in temperature would be a physical change.

Precipitation produced would be chemical reaction, and if no precipitation was produced, that would be physical.

And then a colour change is characteristic of a chemical reaction and no change in colour would be a physical change.

So you might want to pause the video just to check your answers here.

So let's have a look at question three.

So Aisha is confused about the difference between physical change and a chemical reaction.

She's written two statements, and what I want you to do is correct her description of a physical change and a chemical reaction using the words in bracket.

So choose the right word, pause the video and rejoin in a moment.

So let's have a look at the answers, see how you did.

So a physical change can be reversed, such as melting ice or freezing.

No new products are made.

And when gold is melted to make jewellery, that's a physical change.

A chemical reaction cannot be reversed.

So a match being burned, we can't get back to the original match.

New products are made, for example, when iron rusts.

That's a different product.

So it's time for the second part of our lesson.

Well done so far.

When a chemical reaction takes place, there will be evidence of the chemical reaction and these will include a change in colour, bubbling, change of temperature, an odour or smell, emission of light, sound, or precipitation.

If there's no evidence for a chemical reaction, then we probably assume it's a physical change.

So you're going to carry out a series of experience now and watch some demonstrations.

Your results table will have the following headings.

So the experiment number, observations, chemical reaction or physical change, and then the reason why you think it's a chemical reaction or a physical change.

So there's your results table.

I want you to decide if each experimental or demonstration shows a chemical reaction or a physical change, and then I want you to give a reason for your decision.

So here are the experiments that you're gonna have a look at.

So pause the video and come back when your table is complete.

So your observations and reasons might be similar to mine.

They won't be identical probably.

So dry ice.

When you look at dry ice, you'll see that it changes from being a white solid to white smoke or gas.

And that is a physical change because if you collected the gas or smoke, you could cool it again to make solid dry ice or solid carbon dioxide.

So this is reversible.

We could go back to dry ice.

The glow stick.

The glow stick glowed when it was snapped.

This is a chemical reaction because when the chemicals mix together, a reaction occurs, a colour change occurs and light is emitted showing that the chemical reaction has occurred, and this is irreversible.

You can't get the glow stick to not glow and then glow again.

The ice cube.

The ice cube melts to form water, and that's a physical change because you could put the water back into the freezer to refreeze it and make ice again.

We haven't got any new products, and so it's a reversible change.

Toasting bread.

The cube of bread changed from being a white to brown where it was toasted.

So that's a chemical reaction.

A colour change shows that a chemical reaction has taken place there, and you can't make the toast back into bread.

This is an irreversible change.

So who knew when you were toasting bread it was a chemical reaction? There you go.

So the match burned brightly and it had a normal orange flame.

This was a chemical reaction because, when the match lit up, burnt with an orange flame, it got hot, the match changed colour, and this is irreversible.

Magnesium in acid.

The magnesium metal got smaller, was used up in the reaction.

Bubbles of gas were produced, and actually the test tube would warm up.

So this is a chemical reaction.

New products are being formed, for example, the gas, temperature change occurred, and it's irreversible.

Citric acid and sodium bicarbonate.

We get bubbles of gas being produced and the temperature actually decreases for this reaction.

So this is a chemical reaction because we've got new products being formed, such as the gas.

We've got a temperature change showing a chemical reaction has occurred, and it's irreversible.

Iodine solution in a starch solution.

The iodine solution is originally an orangy brownie colour.

And when you add it to starch, it goes really black.

So this is a chemical reaction because we've got a colour change and it's irreversible.

When we dissolve sugar in water, the sugar disappears as it's dissolving in water.

This is a physical change.

We could recover the sugar by evaporating all the water.

So this is a reversible change.

The sugar hasn't disappeared.

It's still there.

It's dissolved in the water, so we can get the sugar back.

If we boil water in a kettle, the water turns to steam when the kettle boils.

This is a physical change and you could collect the steam and cool it back so it condenses back into liquid water.

So it's reversible.

And then finally, the indoor firework, sparks and flames can be seen from the top of the firework and the firework gets hot.

That's a chemical reaction.

Sparks and flames show that new products are being formed.

The temperature change shows a chemical reaction has occurred, and this is an irreversible change.

We can't get the sparkler back to how it was.

Well done.

How did you do? Did you get them all right? Fantastic if you did.

So we've come to the end of the lesson today, So, hopefully, you know a lot more about chemical reactions and physical changes.

So let's have a look at the summary of today's learning.

So characteristics of chemical reactions include changes in colour, bubbling, or a change in temperature.

Bubbles appear when a gas is produced in a chemical reaction, and remember that word, effervescent, if you ever hear it.

Again, that means fizzing or bubbles are happening.

In a chemical reaction, atoms rearranged themselves to form new substances, and we looked at methane and oxygen, and showed how the atoms there were rearranged when they reacted.

And generally, pretty much chemical reactions are all irreversible.

You can't reverse the reaction.

So I hope you feel a lot more confident about the difference between chemical reactions and physical change now, and I look forward to seeing you next time.

Well done.