Lesson video

Hello, I am Mrs. Adcock and welcome to today's lesson.

Today's lesson title is State Changes: Fundamentals.

How can we use the particle model to explain changes of state? Today's lesson outcome is I can describe the processes of melting, freezing, boiling, and condensation, using a simple particle model to explain these state changes.

Some of the key words we will be using in today's lesson include melting, freezing, forces of attraction, boiling and condensing.

Here you can see each of those keywords are written in a sentence.

It would be a good idea to pause the video now and read over those sentences.

You might even like to make some notes so that you can refer back to them later in the lesson if needed.

Today's lesson on state changes: fundamentals is split into two main parts.

First of all, we are going to be looking at the state changes, melting and freezing, and then in the second part of the lesson, we are going to be looking at the state changes, boiling and condensing.

Let's get started on the first part of our lesson, melting and freezing.

Particles in a solid state are in a fixed position and the particles cannot move past each other, they can only vibrate about these fixed positions.

Substances in the solid state are able to lose and gain energy, and we can see two images there.

These are particle models showing the particles in the solid state and liquid state.

When a substance in the solid state gains energy, usually by heating up the substance, then the particles are now able to move more and the particles are able to overcome the forces of attraction that were holding them together in those fixed positions.

So the particles can now move past each other and the substance will have gone from being in the solid state to now being in the liquid state.

And the substance will have melted.

So the change of state when we go from the solid state to the liquid state is known as melting.

When melting occurs, the individual particles remain the same size and shape.

If you look at the particle models for the solid state and the liquid state, you'll see the particles have been represented by solid circles.

And in the solid state and the liquid state, these particles have remained the same size and the same shape.

The temperature at which a substance changes from the solid state to the liquid state is called the melting point.

The melting point of water at which it changes from ice in the solid state to water in the liquid state is zero degrees Celsius.

In this animation, we can see a substance in the solid state.

You'll notice that the particles are in a regular arrangement.

As heat is applied to this substance, the particles gain energy, they are able to overcome some of the forces of attraction.

And the particles are able to move more.

The substance will then turn from being in the solid state to the liquid state.

Candle wax melts and becomes molten, which is melted wax, at approximately 67 degrees Celsius.

Therefore, the melting point of wax is 67 degrees Celsius, and this is the temperature at which the wax changes from the solid state to the liquid state.

Different substances have different melting points as the energy needed to overcome the forces of attraction between the particles in a substance are different.

For example, the melting point of gallium is 30 degrees Celsius.

The melting point of gold is 1064 degrees Celsius.

The melting point of silver is 962 degrees Celsius.

In the image here we can see some gallium melting in the palm of someone's hand, and that's because the melting point of gallium is 30 degrees Celsius.

In these examples, the forces of attraction are strongest between the gold particles.

And we know this because the gold has the highest melting point out of those three metals there.

Gold has a melting point of 1064 degrees Celsius.

And this is because it requires more energy to overcome those forces of attraction, to enable the substance to change from the solid state to the liquid state.

And in those examples, the forces of attraction are weakest between gallium particles.

How do we know this? Because gallium has the lowest melting point of those three metals.

It has a melting point of 30 degrees Celsius, and that's because it requires less energy to overcome those weaker forces of attraction.

When a substance in the liquid state loses energy, usually by cooling, the particles move less.

So this time rather than heating a substance, we are cooling the substance.

And when we call the substance, the particles lose energy and they move less.

The particles are now not able to overcome the forces of attraction that exists between the particles and the particles can only vibrate in a fixed position.

The substance will now be in the solid state and will have frozen.

So if we take a substance in the liquid state and cool it down, then the particles will move less and they will vibrate only in their fixed positions and the substance will have changed from being in the liquid state to the solid state.

And this process of changing from the solid state to the liquid state is known as freezing.

When freezing occurs, the individual particles remain the same size and shape.

If we look at the particle model there for the solid state and liquid state, we can see that when we go from the solid state to the liquid state, this change of state is known as melting.

And when we go from the liquid state to the solid state, this change of state is known as freezing.

We have seen that the melting point is the temperature at which a substance changes from the solid state to the liquid state.

So what is the freezing point? The freezing point is the temperature at which a substance changes from the liquid state to the solid state.

And the melting and the freezing point are the same temperature for a substance.

The melting point for water in the solid state is zero degrees Celsius.

At zero degrees Celsius water can melt and change from ice, which is water in the solid state to the liquid state.

The freezing point for water in the liquid state is also zero degrees Celsius.

The melting and freezing point for a substance are the same temperature.

In the animation here we can see we have a substance in the liquid state.

And as we cool this substance, the particles have less energy and therefore they move less and the particles move into a regular arrangement where they can only vibrate about a fixed position.

So the substance changes from the liquid state and as we cool it down, it changes to the solid state.

Time for a question.

When a substance melts, it changes from; A, a solid state to a gas state, B, a solid state to a liquid state, C, a liquid state to a gas state.

The correct answer is B.

Well done if you choose answer B.

When a substance melts, it changes from a solid state to a liquid state.

The temperature at which a substance changes from the solid state to the liquid state is known as the melting point.

Let's have a go at another question.

Is this statement true or false? The melting point for a substance is 45 degrees Celsius.

At 25 degrees Celsius, so that's below the melting point, the particles will be able to move past each other.

That statement is false.

Can you justify your answer and explain why that statement is false? Is it A, because the particles will be in the solid state so they will be vibrating in a fixed position until they melt? Or is it B, the particles will be in the gas state so the particles will have overcome the forces of attraction and move in all directions? The correct answer is A, at 25 degrees Celsius, the substance will be in the solid state.

It has not yet reached its melting point, and therefore it has not changed into the liquid state yet.

A says the particles will be in the solid state, so they will be vibrating in a fixed position until they melt.

The particles are not able to move past each other in the solid state due to the forces of attraction between the particles.

Well done if you got that question correct.

Another question for us to have a go at here.

When using the particle model, what would an individual particle look like when a substance in the solid state has melted? Will it look like the image shown in A, B or C? The correct answer is C.

We use solid circles or spheres to show the particles in the solid, liquid and the gas state.

The particles do not change shape or size regardless of whether they are in the solid state, the liquid state, or the gas state.

Time for our first practise task of today's lesson.

For this task, you have got six descriptions and you need to match these descriptions to the changes of state.

Do they describe melting or freezing? Pause the video now and have a go at answering this question.

Let's go over the answers before we move on to question two.

Particles lose energy, this occurs in freezing.

Particles gain energy, occurs during melting.

The particles move more also occurs during melting.

So the particles gain energy, they move more, they can overcome some of the forces of attraction and the substance will change from the solid state to the liquid state.

The particles move less during freezing.

As the substance is cooled, the particles have less energy and they move less.

Changing from the liquid state to the solid state is freezing.

And changing from the solid state to the liquid state is melting.

Well done if you correctly matched those descriptions to the changes of state.

For question two, we need to correct Aisha's statements.

Aisha has made four statements here.

They are, "The particles in the substances melt and change shape." "When a substance freezes, the particles move past each other slowly." "When a substance melts, the particles stop moving completely." And finally, "Melting is a change from the liquid state to the solid state." So pause the video now.

Read over Aisha's statements again and then if you can reword them to correct Aisha's statements.

Let's go over the answers.

The particles in the substances remain the same size and shape when we have a change of state.

When a substance freezes the particles vibrate in fixed positions.

When a substance melts, the particles can move past each other.

And melting is a change from the solid state to the liquid state.

Hopefully you have reworded Aisha's incorrect statements so that they are all correct.

We have had a look at the state changes melting and freezing.

Now we are going to move on to have a look at boiling and condensing.

When a substance in the liquid state gains energy, usually by heating, the particles move more, are able to overcome the forces of attraction with other particles and can move quickly.

The particles are now able to move in all directions.

So they've overcome those forces of attraction, the particles are moving more, they are moving quickly, and they are moving in all directions.

The substance will now be in the gas state and will have boiled.

So when we take a substance in the liquid state and we heat it up, the particles gain energy and the substance changes from the liquid state to the gas state.

And this change of state is known as boiling.

The individual particles remain the same size and shape.

We can see this in our model which shows particles in the liquid state and the gas state.

The particles are represented by solid circles and the solid circles are the same size and shape in the liquid state and the gas state.

When boiling a liquid, the particles changing to the gas state become bubbles.

The bubbles are released into the surrounding air.

In the image we can see we have water in the liquid state and this water has been heated.

The particles will have gained energy.

They have overcome the forces of attraction holding them together, and we have formed water in the gas state.

We know this because we can see bubbles have formed and these contain water in the gas state.

Water in the gas state is called steam.

Here we can see bubbles rising to the surface and the steam will be released into the surrounding air.

The temperature at which a substance changes from a liquid state to a gas state is called the boiling point.

We have already learned earlier in the lesson about the melting point, which is the temperature at which a substance changes from the solid to the liquid state.

We have learned about the freezing point and the freezing point is the temperature at which a substance changes from the liquid state to the solid state.

And now we have also learned about boiling point.

So this is the temperature at which a substance changes from the liquid state to the gas state.

Different substances have different boiling points depending on the strength of those forces of attraction.

We can see here that the boiling point of water is 100 degrees Celsius.

The boiling point of liquid nitrogen is negative 196 degrees Celsius.

The boiling point of water is higher than the boiling point of liquid nitrogen, and that tells us that the forces of attraction between the water molecules are stronger than the forces of attraction between nitrogen molecules.

When a substance in the liquid state boils, it takes up a much larger volume.

It expands many times its own volume.

There is only between the particles and the particles stay the same size and shape.

We can see this in the animation where we have a substance in the liquid state.

And we heat that substance.

And as we heat the substance, the particles gain energy, they move more and the particles spread out moving quickly in all directions.

The substance has changed from the liquid state to the gas state, so boiling has occurred.

Time for a question.

The boiling point of a substance is the temperature at which it, A, changes from a solid state to a liquid state.

B, changes from a liquid state to a solid state.

C, changes from a gas state to a liquid state or D, changes from a liquid state to a gas state.

The correct answer is D.

So well done if you chose answer D, the boiling point of a substance is the temperature at which it changes from a liquid state to a gas state.

A, the temperature at which a substance changes from the solid state to a liquid state would be the melting point.

B, the temperature of which a substance changes from a liquid state to a solid state would be the freezing point and remember the melting point and the freezing point occur at the same temperature.

Here's another question for us to have a go at.

Ethanol in the liquid state, when heated will boil at 78 degrees Celsius to form bubbles.

What is inside the bubbles of boiling ethanol? Is it water in the gas state, ethanol in the gas state, nothing, only empty space or air? The correct answer is B, Ethanol in the gas state.

When ethanol in the liquid state is heated and reaches its boiling point, the ethanol will change from being in the liquid state to the gas state.

It will form ethanol in the gas state inside bubbles and the bubbles will be released into the surroundings.

Let's have a look now what happens when we cool a substance in the gas state.

When a substance in the gas state loses energy, usually by cooling the particles move less, are not able to overcome the forces of attraction with other particles.

The particles now touch surrounding particles and the particles can now slide past each other.

The substance will now be in the liquid state and will have condensed.

If we look at the images there, we can see we have the particle model showing the liquid state and the gas state.

When we heat a substance in the liquid state, then boiling can occur where our substance changes from a liquid to being in the gas state.

If we have a substance in the gas state and it loses energy usually from being cooled down, then the substance can go from being in the gas state to being in the liquid state, and this is known as condensing.

The individual particles remain the same size and shape.

When condensing occurs, those particles in the gas state move less, they're now touching each other.

They can slide past each other and they can't overcome all those forces of attraction.

But the particles have not changed size or shape.

You can often see condensation on windows and mirrors.

Here we can see condensed steam on a window.

This is where steam, water in the gas state, has cooled down and formed water in the liquid state.

The temperature at which condensing occurs is called the condensing point.

It is the same temperature as the boiling point.

The boiling point of water is 100 degrees Celsius.

The condensing point of steam is also 100 degrees Celsius.

Commonly, scientists only refer to the melting and boiling point of substances, but we know that for a substance, the melting and the freezing point will be the same temperature.

And also the boiling point and the condensing point will be the same temperature as each other for a substance.

When a substance in the gas state condenses, it takes up a much smaller volume, there is no space between the particles and the particles touch each other.

Remember, the particles stay the same size and shape.

We can see this in the animation where we have a substance in the gas state and this substance is cooled, so the particles will now have less energy.

The particles move closer together until they are touching each other and the substance is now in the liquid state.

Time for a question.

The condensing point of a substance is the temperature at which it, A, changes from a solid state to a liquid state.

B, changes from a liquid state to a solid state.

C, changes from a gas state to a liquid state.

Or, D changes from a liquid state to a gas state.

The correct answer is C, the condensing point of a substance is the temperature at which it changes from a gas state to a liquid state.

Hopefully you can identify that statement A refers to the melting point.

Statement B refers to the freezing point and statement D refers to the boiling point.

Well done if you got that question correct.

Time for our final practise task of today's lesson, and first of all, you need to add labels in the boxes to show the changes of state.

We have the particle model there showing particles in the solid state, the liquid state, and the gas state.

You need to label the boxes to show the changes of state.

Let's see how you got on.

When a substance changes from the solid state to the liquid state, this is melting.

When a substance changes from the liquid state to the solid state, this is freezing.

When a substance changes from the liquid state to the gas state, then boiling has occurred.

And when a substance changes from the gas state to the liquid state, this change of state is called condensing.

Well done if you correctly labelled those four changes of state.

Question two, select the correct option from the brackets to describe condensing and boiling.

If you pause the video now and have a go at answering this question, then when you come back, we will go over the answer.

Let's see if you've answered this question correctly.

In condensing the particles move closer together and in boiling the particles move further apart.

In condensing the particles lose space between them and in boiling the particles gain space between them.

In condensing the substance decreases in volume, and in boiling a substance increases in volume.

Well done if you got that question correct.

Here is our final question of this task.

Use the information in the table, complete the state of matter of the substances at room temperature.

We have got five different substances.

We have information on their melting point and boiling point, and you need to decide what state of matter these substances are at 25 degrees Celsius.

Pause the video now and have a go at answering this question.

The correct answers are water will be in the liquid state at room temperature.

Ethanol will be in the liquid state.

Bromine also in the liquid state.

Oxygen will be in the gas state.

And gallium will be in the solid state.

Hopefully you got this question correct and you were able to identify the state of matter of the substances.

We have reached the end of today's lesson on state changes: fundamentals.

Let's just summarise some of the key points we have covered in today's lesson.

A simple particle model explains melting, boiling, freezing, and condensing processes.

Boiling is when a liquid becomes a gas throughout forming bubbles.

Condensation is when gas turns into liquid.

Melting is when a solid turns into a liquid with added energy.

Freezing is when a liquid turns into a solid losing energy.

In all states, the particles remain the same size and shape as the particles do not have bulk properties like melting and boiling points.

Well done for all your hard work throughout today's lesson.

I hope that you've learned lots during today's lesson, and I hope you're able to join me for another lesson soon.