Hi, I'm Mrs. Hudson, and today, I'm going to be teaching you a lesson called "State Changes: Evaporation and Sublimation." This is a chemistry lesson and it comes under the unit titled, "State Changes." So let's get going.

The outcome of today's lesson is: I can explain the processes of sublimation, deposition, and evaporation, and discuss the energy changes involved in these state changes.

During today's lesson, there will be some key words that are frequently used throughout the lesson, and those are: sublimation, deposition, and evaporation.

So let's have a closer look at what each of those words mean.

Evaporation is when a particle of a substance in the liquid state at the surface has enough energy to change to the gas state and mix with air.

Sublimation is a change of state of a substance from a solid directly to a gas, for example, iodine.

Deposition is when a substance changes from the gas state to the solid state without being in the liquid state.

If you want to make a note of those keywords now, then please do.

Pause the video and then press play when you're ready to carry on.

Today's lesson is going to be split up into three different parts.

In the first part of the lesson, we're going to look at sublimation and deposition, then we're going to move on to look at evaporation, and then in the final part of the lesson, we're going to be doing an evaporation practical.

But let's start with sublimation and deposition.

Some substances change directly from a solid to a gas state without becoming a liquid state, and this is called sublimation.

So we can see here a diagram of the different states of matter.

So we've got the solid state, and the liquid state, and the gas state, and then the arrows are representing the changes of state between the different states there.

So the solid state will melt to become the liquid state, and then the liquid state will boil to become the gas state, the gas state will then condense to become the liquid state, and the liquid state will freeze to become the solid state.

And what can happen is that substances in the solid state can become gas without existing in the liquid state, and this is called sublimation.

And remember that particles in the gas state have the highest energy, so therefore, there needs to be an input of energy for sublimation to occur.

Carbon dioxide in the solid state undergoes sublimation to the gas state without being in the liquid state at room temperature and pressure.

So here we can see an image where some solid carbon dioxide has been added to water, and what has happened is that solid carbon dioxide has undergone sublimation and turned from a solid state straight into the gas state.

Carbon dioxide sublimation properties are used in the following ways: For smoke effects in drink, because you can see in that image there that when the carbon dioxide is in the gas state, it creates this smoky like look.

Also to create a suffocating environment for insect and rodent pest control.

And then also, it can be used for special effects in stage performances.

So we can see there that you've got an image of someone performing on the stage and the sublimation of carbon dioxide is used to create that smoky look for the special effects.

Let's just quickly check our understanding.

Which state of matter has the highest energy? A, the solid state, B, the liquid state, or C, the gas state? This is C, the gas state.

Well done if you've got that right.

So far, we have talked about sublimation being the change of state directly from solid into the gas state without the substance becoming a liquid.

Some substances change directly from a gas to a solid state without becoming a liquid state, and this is called deposition.

So deposition is the opposite of sublimation, and we can see that sublimation is labelled on this image here.

But if we were going to label deposition, the arrow would go from the gas state straight to the solid state.

So we know that sublimation is the change of state from solid directly into the gas state, and deposition is the change of state from the gas straight into the solid state.

And in both of these examples, the substance does not enter the liquid state.

Let's check our understanding of this so far.

Sublimation is a state change where a substance changes: A, solid state to liquid state, B, solid state to gas state, C, solid state to liquid state to gas state, or D, gas state to solid state? This is B, sublimation is the change from solid state straight into the gas state.

So in sublimation and deposition, the substance will not exist in the liquid state at all, so therefore A and C are wrong, and D is describing the change of states from gas to solid, which is deposition.

Fantastic job if you've got that right.

We all ready now to move on to the first task of the lesson.

So you can see that there are three boxes and the first box has had the particles filled in.

And in part one, you need to complete the particle model diagrams and add on labels and arrows, where needed, to show: A, solid state, liquid state, gas state; and B, oiling, condensing, freezing, melting; and C, deposition and sublimation.

Now, if I was you, I would draw the particles the same size as what is in the left hand image to help you.

I'm sure you're going to do a really fantastic job.

Pause the video now and then press play when you are ready for me to go through the answers.

Let's see how we did.

So in the first part of task A, you had to fill in the particle diagrams, and your diagrams should have looked like this.

So the solid diagram was already done for you.

And then in the middle diagram, you should have had roughly the same number of particles.

They were touching each other, which we can see in this diagram, but they don't have that regular arrangement.

And then in the right-hand square, you should have a lot fewer particles, so there's three here, and there's lots of space between them and they are randomly arranged.

And then you should have labelled those as a solid state, the liquid state, and the gas state.

So well done if you manage to get those right.

And then melting, the arrow is pointing from the solid state to the liquid state, and freezing, the arrow is pointing from the liquid state to the solid state.

Boiling is showing the liquid state going into the gas state, and condensing is showing the gas state into the liquid state.

And finally, sublimation is the solid straight to the gas state, and deposition is the gas state straight into the solid state.

Fantastic job if you manage to get all of those right.

If you need to pause the video to add anything into your answer or correct anything, please do, but we're going to carry on now with the rest of the lesson.

Great job so far.

We know about sublimation and deposition, so let's now look at evaporation.

We've got a picture here of a puddle on a road.

This puddle contains water.

It will never reach the boiling point of water, but the puddle will disappear and dry up.

This happens by a process called evaporation.

So before we look at evaporation in more detail, let's look at a word in that sentence that's called the boiling point.

Now, the boiling point of water is 100 degrees Celsius, which is very hot.

When you boil the water in a kettle, it is very hot.

And we know that from the puddle on the road, when it evaporates, the temperature of the surroundings is not 100 degrees.

So how does that happen? Evaporation occurs because in the liquid state, different particles have different amounts of energy.

So that puddle is made up of millions and millions of particles of water, and each of those particles have got different amounts of energy.

And we can see here we've got a beaker, which is showing you some of the particles.

It's not all of the particles, it's just showing you so to help you understand.

But we can see that some of those particles are escaping the water and entering the atmosphere.

And it's the particles with the most energy at the surface of the water that will escape.

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

Particles with the most energy leave the liquid and become a gas.

Eventually, all the particles will have enough energy to be in the gas state and the puddle will dry up.

So what is happening effectively is that the particles at the surface of the puddle have the most energy so they have enough energy to leave the liquid and become a gas.

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

Particles only leave from the surface of the liquid.

More of the particles will have enough energy to be in the gas state, and evaporation will be faster if the temperature is higher.

So in general, the higher the temperature, the faster the rate of evaporation, and that's because more of the particles at the surface will have enough energy to leave and turn into a gas.

Let's check our understanding of evaporation.

Evaporation is when a substance.

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

This is D, evaporation is when a liquid turns into a gas.

Fantastic job if you got that right.

True or false now.

All particles in a liquid have the same energy.

True or false? This is false.

Now, justify your answer.

A, some particles have enough energy to overcome the forces of attraction and change to the gas state, or B, no particles have enough energy to overcome the forces of attraction and change into the gas state? This is A, only some of the particles have enough energy to overcome the forces of attraction and change to the gas state.

If no particles had enough energy, then no evaporation would be taking place.

Fantastic job if you got that right.

Next question.

The freezing and boiling points of water are zero degrees and a hundred degrees, respectively.

Evaporation of water takes place.

A, when the water is below zero degrees, B, when the water is over zero degrees but less than a hundred degrees Celsius, or C, when all the water is heated to a hundred degrees Celsius? This is B, evaporation takes place when water is over zero degrees but less than a hundred degrees.

Fantastic job if you manage to get that right.

We're ready now to move on to task B of the lesson.

For part one of the task, compare boiling and evaporating by sorting the statements into the table.

So this is the table here.

You've got only evaporating, evaporating and boiling, and only boiling.

And these are the statements: Liquid state to gas state, bubbles of gas produced, substance at the boiling point temperature or above, all particles have enough energy to be in the gas state, substance is at a temperature between melting and boiling points, particles gain energy, happens at the surface only, and some particles have enough energy to be in the gas state.

So you need to sort those statements out to say if they apply only to evaporating, if they apply to evaporating and boiling, or if they only apply to boiling.

Sure you're going to do a really great job, so pause the video and press play, ready for me to go through the answers.

Let's see how we did.

So only evaporating, the statements were: happens at the surface only, the substance is at a temperature between melting and boiling point, and some particles have enough energy to be in the gas state.

For evaporating and boiling, we're going from liquid state to gas state, that applies to both evaporating and boiling, the particles have to gain energy for this to happen.

And only for boiling, bubbles of gas produced.

If you boil a substance, you will see bubbling, but that will not happen in evaporation.

We don't see puddles of water bubbling on the floor.

And all particles have enough energy to be in the gas state.

That is true for boiling.

And the substance is at the boiling point temperature or above.

Fantastic job if you manage to get those right.

Really big well done.

We're ready now to move on to the second part of task B.

It is lunchtime and Jun has spilled his water in the playground.

It is a sunny day.

At the end of the school day, the spilled water is not there.

Explain why the surface of the playground is now dry.

Include the words: particle, or particles, and energy in your answer.

I'm sure you're going to do a fantastic job.

Give this your best go now and then press play, ready for me to go through the answers.

Let's see how we did.

So all particles do not have the same energy in the spilled water.

Some particles will have enough energy to be in the gas state and evaporate.

As the sun shines on the puddle, more particles will have enough energy to be in the gas state and evaporate.

Eventually, all the particles end up in the gas state and the spilled water will have totally evaporated.

You might have also added into that answer that the particles escaping will be at the surface of the spilled water.

Fantastic job if you manage to get most of that right.

If you want to pause the video to just check that you've got all the detail into your answer, then please do, but we're going to move on now to the final part of our lesson.

Great job so far.

So we know about sublimation and deposition, we've just talked about evaporation, so now let's have a go at an evaporation practical.

Different substances evaporate faster than others and need differing amounts of energy to evaporate.

So what that means is certain substances, the particles will have to have a bigger input of energy in order for them to escape the surface of the water and turn into a gas.

Ethanol is a type of alcohol; it is used in hand gel.

And it evaporates faster than water.

Propanone, which is in nail varnish remover, evaporates faster than alcohol and water.

So if we were going to order these substances from the quickest to evaporate to the slowest, propanone is the quickest, then ethanol, and then water.

With this in mind, let's check our understanding.

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

What do you predict will be observed after four hours in a warm room? A, whether water level is higher and the propanone has completely evaporated, B, the water and the propanone have completely evaporated, C, the water and the propanone levels remain the same, and D, the water has evaporated but the propanone level has remained higher.

This would be A, and the reason for this is that the propanone evaporates more easily than the water, so therefore the propanone will have all evaporated within the four hours, but some of the water will have remained.

So fantastic job if you recognise that.

Well done.

We are now going to put that theory to the test by carrying out an evaporation practical.

So carry out this experiment to compare the rate of evaporation of propanone at different temperatures.

So step one, we're going to place one drop of propanone on a microscope slide at room temperature and then start a stop drop.

And we can see there we've got an image of pipette, the rectangle is a slide.

So you're going to very carefully place one drop of propanone on the microscope slide at room temperature, and then you're going to start a stop clock.

Step two, stop the stop clock when all the propanone has evaporated and record your results.

So this means you're going to have to very carefully look at the propanone and decide when there is no more propanone left on the slide and then stop your stop clock.

And then you will record how long it took for all of your propanone to evaporate.

Then step three, you're going to warm a microscope slide by placing it in warm water, and then dry the slide and repeat steps one and two.

So you're going to place another drop of propanone on the warm slide and time how long it takes to evaporate.

And then step four, you are going to cool a microscope slide by placing it in iced water.

You're going to dry the slide and then repeat steps one and two again.

So place one drop of propanone and time how long it takes to evaporate.

Now, once you've done the experiment, you need to be recording your results and come up with a conclusion.

So there is a table here for you to fill in.

The temperature of the microscope slide is cold, room temperature, and warm, and then the time taken for the propanone to evaporate in seconds.

And then you're going to complete the sentence to write your conclusion.

Use the words particle and energy in your explanation.

And as a sentence starter here to help you get going.

The propanone on the something slide evaporated the fastest, this is because.

And then finish your answer.

Give this your best go and then press play when you're ready for me to go through the answers.

Let's see how we did them.

So I'm going to put some rough times up here, but yours might be different to this.

It doesn't have to be exactly the same.

So for the temperature when it was cold, the time taken for the propanone to evaporate could be around about 600 plus seconds, so greater than 600 seconds, at room temperature, around about 300 seconds, and on the warm slide, around about 60 seconds.

But you should see a trend of where the cold has the highest number of seconds, the room temperature is in the middle, and the warm slides took the least amount of time for the propanone to evaporate.

Then you're going to complete the sentence.

So the propanone on the warm slide evaporated the fastest, and this is because more of the particles had enough energy to be in the gas state and evaporate from the surface of the drop.

Fantastic job if you manage to get that right.

Really well done.

Let's summarise everything we have learned so far today.

So today's lesson was "State Changes: Evaporation and Sublimation." And we started off by saying that sublimation is the change from solid to gas, and deposition is the change of state from gas to solid, and that both of them bypass the liquid estate.

Sublimation and deposition occur at specific conditions of temperature and pressure.

Energy changes in sublimation/deposition are similar to melting and freezing, but happen directly between solid and gas.

And evaporation is when a liquid changes to gas at the surface as particles gain enough energy to overcome forces between the particles.

I've really enjoyed today's lesson.

I hope you have too, and I look forward to seeing you next time.