Lesson video

Hello.

My name is Mrs. Mytum-Smithson.

I'm pleased that you've come along to learn changes of state: energy and evaporation with me today.

Today's lesson is all about what happens when substances change state.

Included in this is also evaporation.

Maybe you know something about this, but perhaps you don't.

But don't worry, we'll go through this bit by bit, and at the end of the lesson you'll be an expert.

Here are today's keywords: energy, evaporation, evaporation rate, alcohol.

On the next slide, there's some sentences that include these keywords, so if you want, pause the next slide, and then press play when you're ready to get learning.

Today's lesson consists of three learning cycles.

Firstly, we're gonna do about energy and changing state, then we're going to move on to evaporation, and finally we're going to talk about evaporation rates.

Our first learning cycle is energy and changing state.

Let's get going.

Different states of matter have got different amounts of energy.

We're going to have a look here and we're going to see the three different states of matter.

So we've got the solid state, we've got the liquid state, and we've got the gas state.

You can see the energy increases from the solid state to the liquid state, and finally the gas state, which has got the highest amount of energy.

Let's see how well you were listening.

Which state of matter has got the greatest energy? Is it the solid state, the liquid state, or the gas state? Pause the video now for some thinking time and press play when you've got an answer.

If you said gas state, well done.

You're absolutely right.

The gas state particles have got the greatest energy.

When particles gain energy, they move more as they've got more energy.

So if you have a look at the diagram that's going to come up, you'll see first of all they start in the solid state and then they gain some more energy.

They start to move more and eventually they can move past each other.

You'll see them now just moving past each other free to move.

That means that they're in the liquid state.

So they can only vibrate on the spot when they're in the solid state, but if they've got enough energy, then they can slide past each other because they overcome those forces of attraction.

Those forces of attraction are what keeps them together held in that fixed position.

So once they've got enough energy, they can slide past each other, meaning that they've melted and that they're in a liquid state.

When a substance melts, the particles gain energy.

Is that true or is that false? Have a little think.

Well done if you said true.

That is true.

When a substance melts, the particles have got more energy in that liquid state than they do in the solid state.

So the particles gain energy and then they can overcome the forces of attraction to move over and past each other, or is it the particles gain energy and vibrate more in a fixed position? So I want you to write A or B.

Pause the video now if you'd like some thinking time.

Press play when you're ready for the answer.

Well done if you said the particles gain energy and therefore they can overcome the forces of attraction and they can move over and past each other.

In the liquid state, the particles can move past each other, but they're held together by forces of attraction.

But what happens if you give them more energy? So if you give them more energy, eventually the substance will start boiling and turn into the gas state.

If you have a look now, you can see that something is melting, it's in the liquid state.

And now it's boiling and it's in the gas state.

So you can see those particles, they gain energy and they can overcome those forces of attraction.

And then when they're in the gas state, they can move freely in any direction.

This is called boiling, and you can see that this substance is now in the gas state.

So a little melting, then it starts to become in the gas state and the particles are free to move around.

Let's have a check for understanding.

Once particles gain enough energy, they can completely overcome the forces of attraction holding them together and move freely in all directions.

The substance then becomes in the: solid state, liquid state, gas state? Pause the video now if you want some thinking time.

Press play When you're ready for the answer.

Well done if you said gas state.

Once they've overcome those forces of attraction, then they are free to move in all directions, and that is in the gas state.

That is boiling.

In the gas state, remember particles move freely in all directions.

If we were to cool that gas, you can see that then those particles lose energy and they start to come together and then they are just able to move freely past each other but they're touching, and this is when they're in the liquid state.

This is called condensing.

So when things move from a gas state to a liquid state by losing energy, they come together and then they're in the liquid state.

Let's do a quick check for understanding.

A substance in the gas state condenses.

Which information matches the description of condensing? Gas state to a liquid state, loses energy, particles move less; gas state to a liquid state, gains energy, particles move more; gas state to a liquid state, loses energy, particles move more? Which one of these matches the description of condensing? Pause the video now, give you some thinking time, and then press play when you're ready for the answers.

Well done if you said A.

Condensing is when something will go from the gas state to the liquid state, losing energy, and therefore the particles move less.

Well done if you got that one right.

In the liquid state, particles touch and they move over and around each other.

However, if they were to lose energy, they would freeze and become in the solid state.

So when the substances lose energy, the particles can no longer overcome those forces of attraction holding them together, and then they will only be able to vibrate on the spot, so vibrate in a fixed position.

You can see this by looking at the animation.

They can only vibrate on the spot when they're frozen in the solid state.

For this, you'll need to select two correct endings for the following statement.

So the statement is, "When particles in the liquid state lose energy "and change to a solid state: "they are no longer able to overcome "the forces of attraction between particles; "they are able to overcome "the forces of attraction between particles; "they can no longer move over and around each other; "they can move over and around each other." So you need to select two of these statements.

Pause the video now for some thinking time and press play to start the video again.

Well done if you selected the correct answers.

When particles in the liquid state lose energy and change for a solid state, they're no longer able to overcome the forces of attraction between particles, which means that they can no longer move over and around each other.

Well done if you got those correct.

Now task A.

So here what you're going to do is you're gonna complete the missing information.

So wherever there's a box, you're going to write what's missing from that box.

Pause the video now, and press play when you've done the task.

Well done for completing this task.

Let's see what was missing from the diagrams. So melting and condensing were written down there and we were missing freezing and boiling.

At the bottom as the energy increases, let's see what we could have written on that arrow.

So something between the solid state and the liquid state that's the same as the freezing point is the melting point.

Then we're looking at what's the same as the boiling point.

It is condensing point.

And finally we're going to put the state that's got the highest energy, and that is the gas state.

Well done if you got all of those correct.

This is the second question of task A.

I want you to complete the table using the information below.

Two have already been completed for you.

So we've got "move over and around each other," "move randomly in all directions," "the highest energy," "the lowest energy," and you're going to put those statements in these boxes.

Pause the video now, complete the task, then when you're ready for the answers, press play.

Well done for completing that task.

Let's go through the answers now.

So we're gonna have a look at the first row, which is the energy of particles.

So the solid state has got the lowest energy.

The liquid state has got more energy than a solid but less than a gas.

So now we're gonna have a look at the gas state, and that must have the highest energy.

So we increase the energy from solid to liquid through to gas.

Now we're gonna have a look at what that means about movement of particles.

So in a solid state, they're vibrating in a fixed position, in a liquid state that can move over and around each other, and in the gas state they can move randomly in all directions.

Well done if you got all of those questions correct.

Well done for completing energy and changing state.

We're now going to move on to evaporation before we look at evaporation rates.

Let's have a look at evaporation.

Water boils at 100 degrees C.

The puddle of water does not ever reach this temperature, but it will disappear.

So you can see on the left-hand side we've got a puddle of water.

On the right-hand side, we've got a dry road.

When all the water evaporates, it changes from the liquid state to the gas state, and then you've got a nice dry road.

We're gonna have a look at how this actually happens.

All particles do not have the same amount of energy, so even though they're all in a liquid state, all the particles have got enough energy to be in the liquid state, which means that most of the particles are in the liquid state.

However, there are a few that have got enough energy to be in the gas state.

So just a few.

So some particles have got enough energy to be in the gas state.

And these particles can leave the puddle and mix with the air as water in the gas state.

So here's our liquid particles, and you can see here three of them have left the surface of that puddle and evaporated.

Let's have a look at an animation showing this.

So here they are in the liquid state.

They've got different amounts of energy and you can see just that one there evaporating off and mixing with the air and going to the gas state.

This is evaporation.

Let's have a quick check for understanding.

A liquid is added to a beaker.

The beaker is left.

Where does evaporation take place? Does it take place at the surface only? Does it take place inside of the liquid only? Or does it take place everywhere in the liquid? Pause the video, have a little think, and press play when you're ready for the answer.

Well done for completing the task.

If you said surface only, you've done really well because evaporation only takes place at the surface.

It doesn't take place inside of the liquid, just at the surface.

For this check for understanding, I want you to select two answers.

So particles of water in a puddle.

Do they all have the same energy? Have some particles with more energy than other particles? Can they leave the puddle at the surface and mix with the air? Or do they always stay in the puddle unless the puddle boils? Pause the video, have a think, press play when you're ready for the answer.

Well done if you said some of them have got more energy than others, so not all particles have the same amount of energy.

And this means that some of them can leave the puddle at the surface and mix with the air.

Now we're going to compare the differences between evaporation and boiling.

So evaporation can happen at any temperature between the melting point and the boiling point.

Boiling can only take place at a specific temperature.

For example, the boiling point of water is 100 degrees C.

That means that something only boils at 100 degrees C.

Evaporation, there's no bubbles that are being formed, so you won't look at that puddle and see bubbles inside of it.

Particles only ever leave from the surface.

Whereas if something's boiling, you can have a look at the bubbles of the substance in the gas state and they're produced within the liquid.

So if you want to know the difference between something evaporating and something boiling, you could observe what temperature it's at and if there's any bubbles produced.

Let's do a quick check for understanding.

Four particles are labelled up high energy and low energy.

So particle one and three have got high energy, particle two and four have got low energy.

During evaporation, particles leave the liquid and mix with the air particles.

The diagram shows a location and energy of four of these particles.

Which particle or particles is or are most likely to leave? So we're looking at the particle or particles that are most likely to leave.

Is it one and two? Is it three and four? Is it one and three? Or is it one only? Pause the video for some thinking time and press play when you're ready for the answer.

Well done if you said one only.

So particle one is near the surface and it's got high energy, so that's the most likely to leave.

Well done if you got that right.

I want you to decide if these statements are right or wrong.

So you're going to say, "I am sure this is right," "I think that this is right," "I think that this is wrong," or, "I'm sure that this is wrong." So statement A, what do you think? Evaporation takes place at a specific temperature.

Boiling produces bubbles of the substance in the gas state.

During boiling only the particles at the surface leave.

During evaporation, the particles mix with particles in the air.

Pause the video to give yourself some thinking time and press play when you're ready for the answers.

Well done for completing the task.

Evaporation takes place at a specific temperature.

That's wrong.

If you remember, evaporation takes place anywhere between the melting point and the boiling point of the substance.

Boiling produces bubbles of the substance.

That is right.

During boiling, only the particles at the surface leave.

That is incorrect.

Particles change from being in the liquid state to the gas state within the liquid itself during boiling.

During evaporation, the particles mix with the particles in the air.

That is absolutely right.

Well done if you got all four correct.

We're going to have a look at the students describing boiling or evaporating.

You're going to state if the student is describing boiling or evaporating, and you're going to explain how you decided.

So we've got Laura is saying, "A liquid is heated.

"The volume reduces.

Bubbles are formed." Sam is saying, "A puddle of water dries on a cold day." Sofia says, "Some water is heated to 100 degrees C.

"The volume of the water reduces." Alex is saying, "A liquid is heated.

"The volume reduces.

No bubbles are formed." So all these statements are correct.

You've just got to decide on if they're talking about boiling or evaporating, and then write a quick sentence to say how you decided.

Pause the video now, then press play when you've completed the task.

Well done for completing that task.

Laura said that she knows that boiling is taking place because she can see bubbles.

Wherever you see bubbles being formed, that means that boiling's taking place.

Sam said that evaporation is taking place because it's below the boiling point of water.

Remember, evaporation takes place anywhere between the melting point and the boiling point of a substance.

Sofia says that boiling is taking place because it's a specific temperature.

So because a specific temperature is given, that means it's to do with boiling.

And Alex is saying evaporation takes place as no bubbles are formed.

Well done if you got all four of those correct and you gave the correct reasons.

You're doing really well.

Well done for working so hard this lesson.

We've now got our last learning cycle.

We've had a look at energy and changing state.

We've had a look at evaporation.

Now we're going to have a look at evaporation rates.

Here's a diagram of evaporation.

We can see here that the particles with more energy have the ability to mix with the air and leave out the surface.

So you can see these two labelled up here because they've not got the same energy as the other particles that are still in the liquid state.

The higher the temperature, the higher the energy of the particles.

So more of the particles will have enough energy to be in the gas state and evaporation will take place faster.

So I've got two diagrams here showing you that at the lower temperature we've got less evaporation, and as we heat up that substance, whatever that substance is, it can evaporate faster.

So in general, the higher the temperature, the faster the rate of evaporation.

I've got a quick check for you now.

The same volume of water at three different temperature was added to three beakers.

The beakers were left in a room at 25 degrees C for two weeks.

So we've got beaker number one at 10 degrees C, beaker number two at 30 degrees C, beaker number three at 95 degrees C.

And then these were left in a room without being heated anymore for two weeks.

In which of the beaker or beakers do you expect the water to have evaporated? Beakers two and three? Beaker one only? Beaker three only? Or beakers one, two, and three? Pause the video, have a think, and press play when you're ready for the answer.

Well done if you said all three of the beakers, beaker one, beaker two, and beaker three would've evaporated.

Some substances evaporate faster than others.

They need a different amount of energy than other substances to evaporate.

We're gonna take a look about two that you might be familiar with.

So we've got ethanol.

Now ethanol is a type of alcohol and it's used in a hand gel and it evaporates faster than water.

Acetone is in nail varnish remover, and this evaporates even faster than alcohol and water.

So if you put three puddles, one puddle of water, one puddle of alcohol hand gel, and one puddle of nail vanish remover, you would find that the nail vanish remover would evaporate the fastest, then the alcohol, then the water.

The same volume of water and acetone are added to two beakers.

What do you predict will be observed after four hours in a warm room? So what do you think you'll see after putting these beakers in a warm room? Will you see that the water and acetone are at the same level; the water and acetone have completely disappeared; the water is still there, but the acetone has disappeared; or the water is disappeared and the acetone is still there? What do you predict? Pause the video for some thinking time, then press play when you've got the answer.

Well done if you said C.

The water would be there.

It might be at a lower level as shown, but the acetone would be completely evaporated because the acetone evaporates faster than the water.

We've got another one that's a bit similar.

Now we've got water and alcohol.

We've added it to two beakers.

What do you think will happen after six weeks? So will the water and alcohol be at the same level? Will the water and alcohol be completely evaporated? Will the alcohol evaporate but leave some of the water? Or will the water evaporate and leave some of the alcohol? This is after six weeks.

Pause the video now for some thinking time, and press play when you've got your answer.

Well done if you said B.

Both the water and the alcohol would've evaporated.

The alcohol might have evaporated faster than the water, but both of them would probably have evaporated after six weeks.

Well done if you got that answer correct.

We've got task C now.

This is the last task.

Only use the words temperature and energy to fill in the gaps to explain why the rate of evaporation is higher in beaker A.

So beaker A is 60 degrees C, beaker B is 20 degrees.

C.

Why is beaker A going to evaporate faster? And you've only got to use the word temperature or energy to fill in the gaps.

So, evaporation takes place from both beakers.

Particles with enough something are able to escape from the liquid.

Beaker A is at a higher something than beaker B.

This means the particles in beaker A have more something.

In both beaker A and beaker B some particles have more something than others.

However, in beaker A more particles have something to escape the liquid.

For this reason, evaporation takes place faster from beaker A.

In general, the higher the something, the faster the rate of evaporation.

Pause the video now, complete the task, and press play when you're ready for the answers.

Let's have a look at how well you've done.

Evaporation takes place from both beakers.

Particles with enough energy are able to escape from the liquid.

Beaker A is at a higher temperature than beaker B, and this means that on average the particles in beaker A have more energy.

In both beaker A and beaker B some particles have more energy than others.

However, in beaker A more particles have enough energy to escape the liquid.

For this reason, evaporation takes place faster from beaker A.

In general, the higher the temperature, the faster the rate of evaporation.

So well done if you got all of those correct.

Let's have a look and see how much we've learned this lesson.

States of matter can have different amounts of energy.

Solid states have the least energy.

Gas states have the most energy.

A substance in its liquid state can evaporate at temperatures below its boiling point.

So here we've got this diagram.

We've got energy increases.

On the left-hand side, it's blue, on the right-hand side, it's red, representing that there's more energy at that end.

So we've got solid state, liquid state, gas state.

Between the melting point and the boiling point, that is when evaporation can come take place.

The hotter the water, the more quickly it evaporates.

And water evaporates at temperatures that are lower than 100 degrees C.

Well done for completing all the tasks in this lesson about energy and evaporation.

I hope to see you some other time.