Lesson video

Hello, again.

My name is Miss Couves, and I am so excited to teach you science today.

In this lesson, we're going to learn about chemical and physical changes, and how to identify whether a chemical change or a physical change has happened.

Let's get started.

In today's lesson, we will start by recapping our previous knowledge.

Then we will look at some examples of physical changes and chemical reactions.

Then we will compare the characteristics of chemical and physical changes.

And finally, we will identify what sort of change has happened.

In this lesson, you will need an exercise book or paper, and a pencil.

If you don't have one of these items, pause the video now and go and get them.

Let's start by recapping off previous knowledge.

Can you remember the properties of solids, liquids and gases? Pause the video to copy and complete the table.

Press play when you're ready for the answers.

Pause the video to tick and fix your answers.

Remember that solids cannot be compressed, they cannot flow, and they cannot change their shape.

Liquids cannot be compressed, but they can flow and they take the shape of the bottom of their container.

Gases can be compressed, and they can flow, and they fill their container.

Why can gases be compressed, but liquids and solids can't? Gases can be compressed because there is space between the particles.

There is no space between the liquids and solid particles, so they can't be compressed.

Pause the video to complete the diagram in your notes.

Press play when you're ready to continue.

Particles in solids are touching and in ordered rows.

In liquid, they are touching and arranged randomly.

And in gases, they are far apart, not touching and moving very fast.

As you increase the temperature, particles have more energy.

Pause the video and label all of the state changes.

Press play when you're ready to hear the answers.

The state change from a solid to a liquid is called melting.

The state change from a liquid to a gas is called boiling.

The state change from a gas to a liquid is called condensing.

The state change from a liquid to a solid is called freezing.

What is a physical reaction? A physical change is a change in the form or arrangement of a substance.

Why is glass smashing an example of a physical change? Glass smashing is a physical change because the form of the glass changes from a large pane to lots of tiny shards.

But the type of substance doesn't change, it is still glass.

Why is paper tearing a physical change? Paper tearing is a physical change because the form of the paper changes from a large sheet of paper to lots of tiny pieces.

But the type of substance doesn't change, it's still paper.

Why is an ice cream melting an example of a physical change? Ice cream melting is an example of a physical change because the form or arrangement changes.

As the particles change from a solid to a liquid, they become less ordered.

So the arrangements of particles are changing, but the types of particles stays the same.

It's still ice cream particles.

What is a chemical reaction? A chemical reaction is a change that forms a new substance.

Let's think about wood burning.

When wood burns, it produces carbon dioxide and water.

Two new substances have been produced.

So this is an example of a chemical reaction.

When a bike rusts, the metal in the bike reacts with the oxygen in the air to form rust.

A new substance rust has been formed, so this is a chemical reaction.

What is formed in a chemical reaction? In a chemical reaction, a new substance is always formed.

Scientists represent chemical reactions using word equations.

A word equation has reactions before the arrow, and product after the arrow.

What are the reactants? The reactants are the substances at the beginning of the reaction.

Point to the reaction in the word equation.

The cookie mix is the reaction because it is the substance present at the start.

What are the products in a reaction? The products are the substances formed in a reaction.

Point to the products in the word equation.

The cookie is the product because it is the substance formed in the reaction.

Let's look at chemical and physical changes in a bit more detail.

What is a physical change? A physical change is a change in the form or arrangement of a substance.

When ice cream melts, the particles loose their ordered arrangement, but the particles are still ice cream particles.

The arrangement has changed but not the type of substance.

Pause the video and write down why paper tearing or glass smashing is a physical change.

Press play when you're ready to hear the answer.

Paper tearing is a physical change because the form of this substance has changed.

Rather than being a large sheet of paper, it is now smaller pieces.

But the type of substance, paper remains the same.

Glass smashing is a physical change because the form of the material has changed.

Instead of being a large pane of glass, it is now lots of tiny shards.

However the type of substance, glass remains the same.

What is a physical change? Give one different example.

Pause the video and write down one example of a physical change.

Press play when you're ready to continue.

You might have said, ice melting, or water boiling, or salt dissolving.

All of these are physical changes because the arrangement of the substance has changed, but not the type of substance.

What is a chemical change? A chemical change is a change that forms a new substance.

What new substances are formed when a match burns? Burning is a combustion reaction.

When wood burns, it produces carbon dioxide and water.

This is an example of new substances being formed.

So wood burning is a chemical reaction.

How does scientists represent chemical reactions? They use word equations.

Pause the video and have a go at writing the three word equations.

Press play when you're ready to continue.

Let's write the word equations together.

For the match burning, what was the reactant in this equation? The reactant was the match, and it was reacting with the air.

So air is also a reactant.

I'm going to use an arrow to represent that my reactants are producing my products.

What are the products when a match burns? When a match burns, the products are carbon dioxide and water.

Let's have a go at number 2.

Number 2 is the cake baking.

What goes on the left-hand side of the arrow? On the left-hand side of the arrow, we put the reactants.

What are the reactants in this reaction? The reactants are the cake mixture.

What is produced in this reaction? A cake is produced in this reaction.

Can you see how I'm making sure that I write all of the reactants on the left-hand side and all of the products on the right-hand side, even if that means I have to write them one underneath the other.

Let's do the third example.

The third example is a bike rusting.

What are the reactants of this reaction? The metal bike reacts with oxygen from the air.

What is produced in this reaction? This reaction produces rust.

Pause the video and give an example of a chemical reaction.

Press play when you're ready to continue.

Did your reaction involves the formation of a new substance? What was the new substance? Can you write a word equation to represent your chemical reaction? Let's compare chemical reactions and physical changes.

A physical change is when the form of a substance or the arrangement of particles changes.

E.

g.

a change of state or dissolving.

These changes are easy to reverse.

So if I melt ice, that's an example of a physical change.

It's really easy for me to change my water back to ice by freezing it.

This is an example of a change that is easy to reverse.

In physical changes we often see a change in appearance.

A chemical reaction, it's when a new substance is formed.

For example, burning or rusting.

They are hard to reverse.

Let's imagine my cake.

When I bake my cake in the oven, it is really difficult for me to get my cake mixture back.

This is an example of a change that is hard to reverse.

In chemical reactions, we also often see a change in appearance.

Pause the video to make notes on physical changes and chemical reactions.

Press play when you're ready to test your knowledge.

Pause the video, and copy and complete the Venn diagram.

Press play when you're ready to check your answers.

A new substance is produced only in a chemical reaction.

The same substance changes form only in a physical change.

There is a change in appearance, in both chemical changes and physical changes.

Chemical changes are difficult to reverse and physical changes are easy to reverse.

Pause the video to tick and fix your answers.

Press play when you're ready to continue.

Let's use our knowledge of chemical and physical changes to identify some changes.

Before we start, let's check our knowledge.

What is a physical change? A physical change is the change in the form of a substance.

Is it easy or hard to reverse? A physical change is easy to reverse.

Can you give me an example of a physical change? A physical change might be a change of state, or dissolving or tearing of paper.

A chemical reaction is when a new substance is formed.

Is a chemical change easy or hard to reverse? A chemical change is hard to reverse.

Can you give me an example of a chemical change? A chemical change might be burning, or rusting, or making a cake.

Pause the video to copy and complete the sentences, to identify whether these changes are chemical or physical.

Press play when you're ready to hear the answers.

Number 1, making toast is a because, number 2, snow melting is a because, number 3, a firework exploding is a because, a car rusting is a because, a puddle evaporating is a because, a fire burning is a because.

If you're struggling to explain why something is a chemical or physical change, have a think back to the definition.

What makes something a chemical or physical change? Making toast is a chemical reaction because a new substance is formed.

Snow melting is a physical change because the substance changes form, but the type of substance change stays the same.

A firework exploding is a chemical reaction because a new substance is formed.

A car rusting is a chemical reaction because a new substance is formed.

A puddle evaporating is a physical change because the arrangement of particles changes, but the type of substance remains the same.

A fire burning is a chemical reaction because a new substance is formed.

You've worked so hard learning about chemical and physical reactions today.

I'm so impressed with all of the work that you have done.

Make sure you've tried the quiz, so that you can show how much you've learned.

See you next time.