Hello there! My name's Mr. Forbes, and welcome to this lesson from the Energy of Moving Particles unit.

And this lesson's called, "A Heating Curve for Water." We're going to look at the process of heating water from the solid state until it turns into a gas, and see the patterns and behaviour of the particles within it.

By the end of this lesson, you're going to be able to use the particle model of matter to describe changes of state such as melting and boiling.

You're also going to look at the pattern of behaviour of a material as it's heated until it turns into a gas.

Here are the keywords that will help you in this lesson.

The first of them is melting, and that's the change of state from a solid to a liquid, and that happens at a particular or fixed temperature for a pure substance.

Then we have boiling, and that's the change of state from a liquid to a gas, and that happens at a different fixed temperature.

And finally, change of state.

And that's changing from a solid to a liquid or a liquid to a gas or the reverse of those processes.

The lesson's in three parts, and in the first part we're going to look at using the particle model for melting and boiling and explaining what's happening to those particles during those changes of state.

In the second part of the lesson, we're going to look at heating water from the solid state.

So taking a block of ice, heating that up until we turn that into a vapour, into water vapour.

And in the final part, we'll look at the results of that experiment and see a pattern in behaviour of a substance as you heat it from a solid all the way into a gas.

So let's get started by looking at the particle model of melting and boiling.

In the particle model, we consider matter to be made up of lots of small particles and those small particles can be represented by circles in diagrams. So if we've got particles of small mass, we can represent them with small circles like this.

And if we've got particles of slightly greater mass, we can have them represented by slightly greater circles.

So bigger circles there.

In reality, particles aren't shaped like circles or spheres at all, but we use them to simplify our diagrams. You may have already seen that the arrangement of particles in solids, liquids, and gases are different and those arrangements and movements of the particles explain the properties of behaviours of those three states of matter.

So in a solid, their particles are in fixed positions and they vibrate around those fixed positions and they have strong bonds between them, strong electromagnetic forces between those particles.

In a liquid, the particles are more free to flow past each other.

So they're still attracted to each other by those electromagnetic forces but those bonds are weaker and the particles can flow past each other so a liquid can change its shape.

And in a gas the particles can move very freely past each other and they're much further apart because there's no strong electromagnetic forces between them.

It's very, very weak or no falses at all.

Let's check your understanding of the states of matter.

I'd like you to match each state of matter with the correct picture, please.

So I've got three pictures at the bottom there and three descriptions of the states just above them, and then the three names of those states at the top.

So just draw lines to connect those please.

Pause video, draw those lines, restart.

Welcome back.

Well, the solid material is where the particles are vibrating in fixed positions.

So you should have drawn a line between A and E.

The liquid are where the particles are close together, but moving freely, so that's a line between B and F.

And finally, the vapour or the gaseous state is where the particles are far apart and moving freely, so you drew a line between C and D.

Well done for doing that.

So if we have a solid, we can change it into a liquid by heating it and that will increase its temperature, then change its state.

And if we continue to heat it, it will again increase in temperature until it then turns into a gas and change its state again.

The reverse process also happens.

If we've got gases, we can cool them and they'll turn into liquids.

And we cool them further, and they'll turn into solids.

Those changes between them are known as changes of state.

We've got solids, liquids and gases, and solids are at the lowest temperature for a material and gases at the highest temperature.

If we heat a solid, it will turn into a liquid.

That process is known as melting.

If we continue to heat and provide it more energy, then the liquid will evaporate and turn into a gas.

If we do the reverse and cool the gas, then the gas will condense and turn back into a liquid.

And if we cool that liquid, that liquid will freeze and turn into a solid.

And they're the general changes between solid, liquid and gases.

There are a few exceptions to that, but we're not looking at those today.

Now we can explain the changes of state by describing what's happening to the particles within the material.

When a solid is heated, its particles begin to vibrate more.

They vibrate faster around their fixed positions and that makes them move very slightly further apart.

So if I start with a solid something like this, at 10 degrees Celsius, and I heat it strongly and increase its temperature to 100 degrees Celsius, then the particles are still the same size, but they've moved very slightly further apart because they're vibrating around their positions more and they'll occupy a bit more of the space around them and push the other particles further away.

If I can continue to heat it, then the particles will move apart even further.

So at 300 degrees Celsius, the particles are further apart again.

The higher the temperature, the greater the speed of vibrations of the particles and the further apart those particles become.

As I've said, the particles themselves don't change size as the temperature increases, just the spacing between them.

Let's check your understanding of changes of temperature for a solid.

I've got figure X there on the right and it's showing the particles in a cold solid.

Which of those figures below, A, B or C, shows the particles in the same solid at a higher temperature? Pause the video, make a selection, and restart.

Welcome back.

Hopefully you selected option B there.

The particles are slightly further apart.

You'll notice they've not got any larger, the spacings between them is increased.

Answer C is incorrect 'cause the particles got bigger.

Answer A is just the same material again, they've not changed at all.

So well done if you selected B.

If you can continue to heat that solid, those particles are gonna move further apart, gain more energy, and eventually they're going to be far enough apart to start to overcome the electrostatic forces that are holding them together.

So at first you've got a fixed structure and shape, the particles are vibrating around that, but eventually the forces between the particles become weaker and they start to be able to flow and move past each other.

So the material is now a liquid, it's changing shape, all its particles are free to flow.

So that solid has melted and become a liquid because the forces between the particles has changed.

So different substances will have different melting points.

They won't all melt at the same temperature.

So we've got a table here showing the melting point of some pure substances.

Now it should not, this is just for pure substances.

If there's any impurities in these, then that will actually have an effect on the melting point.

So the pure water has got a melting point of zero Celsius.

Ethanol has got a much lower melting point.

Nitrogen has got a very low melting point, and mercury's got the lowest one.

But metals like gold and tungsten are very high melting point.

You see tungsten there at over 3,000 degrees.

They're solid when they're below that temperature.

So any sample of pure water that's below zero degrees Celsius will be a solid, and the same for gold.

Any sample of pure gold below 1,064 will be a solid.

And impurities, as I've said, will have an effect on that melting point.

Okay, let's see if you understood that idea about melting points.

Izzy's got a sample of pure ice.

What could its temperature be? So you've got three options there.

A, B, and C.

I'd like you to pause the video, make a decision, and restart.

Welcome back.

Well, hopefully you selected C.

The ice has got to be zero degrees Celsius or lower.

Okay, it can be at zero degrees Celsius, but it could be at any temperature below that.

So when you take ice from a freezer, it's at a temperature of minus 10 or lower perhaps.

So well done if you selected C.

When a liquid reaches its boiling point, there's going to be a change in the behaviour of the particles again.

They're going to be able to completely overcome the forces between them and become totally free of each other.

So here we have our liquid.

There's still forces between those particles, why it stays together, but it still flows.

But as we heat that liquid up, they're gonna start to move further apart and eventually some of those particles are gonna gain enough energy to escape.

And if you keep on heating, all of the particles escape from the liquid and have no forces between them anymore.

They move around quickly and freely.

They become a gas.

And that happens at the boiling point.

Just as solids have particular melting points, liquids have particular boiling points.

So we've got some examples here.

Again, these are for pure samples.

If there's impurities, these values might change.

And pure water's got a boiling point of 100 degrees Celsius.

And you see ethanol boils at a lower temperature.

Nitrogen is boiling at minus 196.

And you can see you could actually boil gold if you raised it to a temperature of closing on 3,000 degrees Celsius there.

So it's very difficult to do.

If the substance is above its boiling point, it must be a gas.

So if I heat ethanol above 78 degrees Celsius, so I'll say 79 or 80 degrees, it's turned into a gas.

Okay, another check for you here.

Water can be in a solid state, a liquid state, or a gaseous state.

Which statement describes what happens as a substance changes state? So pause the video, make your selection, and then restart please.

Welcome back.

Hopefully you selected the attraction between the particles in the materials changes.

So there's a change in those attractions between particles and that accounts for the changes of state.

Let's test if you can apply that knowledge.

I've got Lucas, he's using a hot grill to make cheese on toast.

What happens as the cheese melts and becomes a liquid? So pause the video, make your decision from those four, and restart.

Welcome back.

Hopefully you selected option D.

The cheese molecules are less attracted to each other.

The forces between them have decreased.

So well done if you selected that.

Okay, it's time for the first task of the lesson.

And what I'd like you to do is to describe the changes of particle behaviour when: A gas condenses to become a liquid, a liquid freezes to become a solid, and the temperature of that solid is gradually decreased.

And you'll notice that those are the opposite to the processes I described earlier in the lesson.

So pause the video, work out your descriptions, and restart please.

Welcome back and let's have a look at the answers to those.

So for a gas condensing, the particles are gonna slow down, move closer together, and the attraction between the particles is going to increase.

But they're still gonna be able to flow past each other because they're still in a liquid state.

When a solid freezes, the particles slow down further, they move much closer together and the attraction between the particles become strong enough so they can no longer flow.

They're just going to be able to vibrate around fixed positions.

And as the temperature's decreased, the speed of that vibration is going to decrease.

They become closer together and the solid's going to contract.

It's going to get slightly smaller.

Well done if you've got answers like that.

And now it's time for the second part of the lesson.

And in it we're going to be heating a solid and turning it into a vapour.

So we can look at the behaviour of the material as it's heating.

We're gonna use water for that.

So we're gonna start with a block of ice and heat it in order to produce what's called a heating curve.

So we can plot that and analyse the behaviour and see what's happening during the changes of state on other parts.

To do that, we need a block of ice, but we need to be able to measure its temperature as accurately as possible.

So we're gonna have a block of ice and perhaps put a small hole in it so that the thermometer when we place it in, like this, is going to allow a close contact between the thermometer and the ice.

So it's actually going to be measuring the temperature of the ice block itself.

Then we're gonna place that ice block inside a beaker so we can heat it up and it can melt and turn into a liquid and the liquid doesn't escape anywhere.

So we're gonna place it into a beaker, something like that.

So I'd like you to explain why is it important that the thermometer is in close contact with the ice and not just the water surrounding the ice as it melts? Pause the video, work out your answer and restart please.

Welcome back.

Hopefully you selected option C.

The solid ice may be at a different temperature than any liquid water surrounding it, so we do need to make sure that that thermometer is in very close contact with the ice so we can measure the temperature of the ice.

Well done if you selected that.

And this is how we're going to heat the ice.

We're going to place it in the beaker and we're gonna put it on a gauze on top of a tripod on top of a heat-resistant mat.

And so we've got basically standard heating apparatus where we're going to be using a Bunsen burner to provide energy to the ice to melt it.

We're going to record the temperature of the ice as we heat it every 10 seconds so that we can have data to plot a graph showing the temperature over time.

And as we're doing the experiment, we are going to make sure that the Bunsen burner provides a constant amount of energy every second.

So once we start the Bunsen heating the ice, we're not going to adjust it in any way.

We're gonna leave it at a constant flame.

During the experiment, obviously the ice is going to melt and we're going to have liquid water.

That liquid water is gonna be contained within the beaker and that's going to be heated and its temperature's going to rise.

And eventually, the temperature of that water is going to reach its boiling point and it's going to start to boil.

Once it's reach its boiling point, basically we've reached the end of the experiment.

We should heat it for a little bit longer to see if there's any further changes in the temperature.

But basically once it's boiling, we're not going to get much more change so we stop shortly after that.

Okay, we've just finished the experiment.

Why shouldn't the equipment be put away immediately after that experiment's concluded? So I'd like you to pause the video, read through those three options, select one, and then restart please.

Welcome back.

Hopefully you selected C.

The equipment needs to be allowed to cool so it's safe to handle.

All of that equipment's gonna become very hot during the heating with the Bunsen, so you mustn't handle it until it's cooled down.

So well done if you selected that.

Okay, now it's time to carry out that experiment and the instructions are fairly simple and placed here.

I'd like you to start with a block ice and heat it till it's boiling.

And you need to be recording the temperature of that ice and the water until it's reached its boiling point a little bit beyond please.

So pause the video, carry out that experiment, and then restart once you've collected all the data please.

Welcome back.

Well, here's the data I collected in my experiment.

My ice started at minus six degrees and I gradually heated it and heated following a pattern like this.

And as you can see, there are several different stages in the heating there.

There's parts where the temperature's rising and a couple of parts where the temperature didn't rise as well.

And we'll analyse those in the next part of the lesson.

So well done if you've got data something like this.

And now it's time for the third and final part of the lesson.

And in it we're going to look at that graph, that heating curve we produced from water, and analyse what's going on in each of those stages.

So let's start that.

So our graph of heating water had a shape something like this.

I've got sections where the temperature rises and sections where they don't.

So there's different sections of the heating of the graph for water.

We can look at each of those sections here.

We got, first of all, in this first section, the temperature of the ice increased evenly until it reached a temperature of zero degrees Celsius.

Once it reached a temperature of zero degrees Celsius, we get the second part of the graph.

And in the second part of the graph, the temperature remained constant while the ice was melting, so the ice was melting during this phase and there's no temperature increase.

Then we have the third part of the graph, and in this part we've got a gradual increase in temperature towards the boiling point again.

So we've got the temperature of the water increasing until it reaches 100 degrees Celsius and a nice even increase there.

But then once it reached 100 degrees Celsius, we've got this section of the graph where, as the water is boiling, its temperature remains constant at 100 degrees.

We can use a graph like that to find a melting and boiling point of a range of substances.

So imagine I've got a different substance here, and this is a graph of its heating curve.

I can find its melting point because that's the point of where it's changing from a solid to a liquid.

So it'd be this part of the graph.

For water, that degree happens at zero degrees Celsius.

For other substances that would be different.

If I needed to find its boiling point, I could look at this point here.

For water, this would be 100 degrees Celsius and it's where the temperature stops changing again.

So I can use the shape of the graft to find melting and boiling points.

As you can see, during those changes of states, melting and boiling, there is no temperature rise.

There's a constant temperature during the melting here and a constant temperature during boiling here.

And that's because the internal energy of the substances is increasing.

I'm heating it, but it's not shown by a increase in temperature.

So there is an increase in internal energy, but we can't see that as a change in temperature.

Something else must be happening inside the material.

Okay, let's see if you can use one of these graphs to find the melting point of substance.

So I've got a graph here of a material.

I'd like you to look at it carefully and decide what's the melting point of that substance.

Pause the video, make your decision, and then restart.

Welcome back.

Hopefully you selected minus 10 degrees.

We've got two possible temperatures here.

The top one, the 80 degrees one, that's the boiling point.

And if you follow the graph backwards between 20 and 40 seconds, you can see there's no change in temperature there.

That must be the melting point.

So well done if you identified that.

And now onto the final task of the lesson.

I'd like you to read through this information carefully.

I've got a scientist heating some paraffin wax and we've got some data about it.

What I'd like you to do is to sketch a graph to show how the temperature of that wax changes as it's heated.

I'd like you to add approximate values to the temperature axis.

You don't need any values on the time axis.

And then suggest how the scientist would know if that sample was pure or not.

So pause the video, answer those questions, and restart please.

Welcome back.

Hopefully your graph looks something like this.

And we've got the same shape as we've seen before.

We've got an increase in temperature, then no temperature increase at the melting point, then an increase in temperature and no further increase in temperature at the boiling point.

And the values you should add to your graph should look something like this.

The boiling point, 370 degrees, and the melting point, 40 degrees.

And you should also label the starting point as 20 degrees Celsius.

So well done if you've got those.

If the sample wasn't pure, then the wax wouldn't melt or boil at the given melting and boiling points in the data.

It'd be slightly different because of the impurities.

So well done if you notice that.

Okay, we've reached the end of the lesson and here's a summary of everything.

We've got our changes of state shown there.

We've got solid melting to a liquid and evaporating to a gas.

We've got the gas condensing to form a liquid and then that liquid freezing to become a solid again.

When a substance changes state, the strength of the electrostatic attraction between the particles changes and the properties of the substance change.

And then we've got a graph showing a heating curve, the temperature changes, and we've got some parts where there's no temperature change, and that's during the changes of state.

Pure substances have fixed melting and boiling points, and the temperature of a pure substance does not change during those changes of state.

Well done for reaching the end of the lesson.

I'll see you in the next one.