Lesson video

Hi, I'm Mrs. Hudson, and today, I'm going to be teaching you a lesson called "Predicting states of Matter".

This is a chemistry lesson, and it comes under the unit titled "States of Matter".

So let's get going.

The outcome of today's lesson is I can predict the state of matter of a substance at different temperatures using the particle model.

During today's lesson, there will be two keywords that are used frequently throughout the lesson, and they are physical change and chemical change.

So let's have a look in more detail of what those words mean.

A physical change is a change in which no new substances are formed, such as a change in state.

For example, melting.

A chemical change occurs when a reaction takes place, and atoms or ions in the reactants are rearranged to make new products or substances.

If you want to make a note of those keywords, then pause the video and then press play when you are ready for me to carry on with the rest of the lesson.

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

In the first part of the lesson, we're going to be looking at physical and chemical changes, and then we're going to use that knowledge to look at the second part of the lesson, which is predicting states.

But let's get going with the first part, physical and chemical changes.

During a physical change, there are changes in particle: arrangement and energy.

So here we can see particles existing in the solid state, they are touching each other, and they can vibrate on the spot and are arranged in a regular arrangement.

Then in a liquid state, the particles are still touching each other, but they are not in that regular arrangement, and the particles are able to move around each other, because they have more energy than the particles in the solid state.

And then finally, we've got the gas state.

And here the particles are arranged randomly.

There is lots of space between the particles, but they are moving around faster, because they have more energy.

So going from the solid state to the liquid state is called melting.

And then going from the liquid state to the gas state we know is boiling.

And as you go from the solid state to the liquid state, to the boiling state, there is an increasing movement of the particles.

And also, there is increasing energy of the particles.

And that is because the more energy particles have, the faster that they will move.

The energy of particles can increase or decrease depending if energy is being added or removed from the system.

So here, we've got our three states.

Again, the solid state, the liquid state, and the gas state.

And if you remove energy from the system, then the gas particles will decrease in energy and they will condense into the liquid state.

And again, if you remove energy from the system, the particles will decrease in energy and they will change from a liquid state into a solid state.

So if you remove energy from the system, there is a decreasing movement of the particles and also a decreasing energy.

A chemical change is different to a physical change, but during a chemical change, chemical bonds are broken and formed, rearranging the atoms or ions making new substances.

So for example here, you've got molecules of hydrogen and oxygen.

And a chemical change is where the bonds that are holding the hydrogen atoms together within a molecule are broken.

And the same would happen to the atoms held within an oxygen molecule.

Those bonds are broken and new bonds are formed, which creates a new substance.

And in this case, you form molecules of water.

And the balance symbol equation here, we can see below is 2H2, which is a gas, plus O2, which is also a gas, and is a chemical change, you make 2H2O, which is a gas.

Now, if we look though at the box that we're saying has the water molecules in, during a physical change, the arrangement of the particles changes, but the chemical bonds between them remain the same.

So in a physical change, you still have the same substance.

So what we're gonna see here is we've still got water.

It's just that the arrangement of the water molecules has changed, and they've gone from being in the gas state where there's a random arrangement, there's lots of space between the molecules, and they've turned into a liquid.

So if you think now what is the change of state called from a gas to a liquid, that's condensation, and that water has condensed, and we can see the molecules of water closer together and touching.

Let's check our understanding so far.

So start with a true or false question.

A chemical change takes place when particles are rearranged, and become bonded to different particles.

True or false? This is true.

Now, you need to justify your answer.

So A, an example of a chemical change is when a substance in the solid state melts to a liquid state, Or B, an example of a chemical change is when magnesium atoms bond to oxygen to become magnesium oxide.

This is B.

So, a chemical change is when particles or ions have the bonds broken, and they are rearranged to become different substances.

Now, in A, this is a physical change, because it's just showing a change of state, whereas a chemical change is when a new substance is formed.

So well done if you manage to get that right.

When nail varnish remover, propanone, evaporates, it is a.

A, physical change.

B, chemical change.

Or C, neither a physical change nor a chemical change.

This is A, it is a physical change.

So when nail vanish is evaporating, it's just a change of state from liquid to gas.

So that is a physical change.

We haven't changed the substance or broken any bonds within the propanone.

Next question, state, what changes occurring between carbon, C, and oxygen, O, to make carbon dioxide, CO2? A, a chemical change.

Or B, a physical change? And we can see that we've got a diagram below to show you what is happening.

This is A, a chemical change.

And can you say why that is the case? This is because atoms are rearranged and bonded to different atoms to make a new substance.

So bonds have been broken and new bonds have been formed to create a new chemical substance, which is carbon dioxide.

Fantastic job if you manage to get that right, well done.

Next question.

State what changes occurring to carbon dioxide.

A, a chemical change.

Or B, a physical change? And you've got a diagram here to show you.

We've got carbon dioxide, and it remains as carbon dioxide.

This is B, a physical change, and can you say why? This is because there's a change of arrangement of particles.

So no new substances have been formed, we haven't broken any bonds or made any new bonds or formed a new substance.

So therefore, this is just a physical change.

Fantastic job if you got that right.

Forces of attraction between particles determine the amount of energy needed for state changes.

For example, melting and boiling.

So here, we've got a substance which is made up of particles, and you can see that the particles arranged closely together in a regular arrangement.

So what state do you think the substance A might be in? That would be a solid, well done if you've got that.

And then you can see that there's some arrows, double-headed arrows within that diagram.

And that is showing you the force of attraction that exists between those particles.

Now, we're only showing you the force of attraction along five different particles there.

But actually, the force of attraction exists between all of the particles within that substance.

So we can see that there's force of attraction that exists there.

And the stronger the forces of attraction between the particles, the more energy is needed to overcome them.

And the higher the melting point is.

And also the higher the boiling point.

So the key bits of information you need from this slide are that particles have forces of attraction between them in a substance, and the stronger the forces of attraction are, the more energy is needed to overcome them.

So therefore, the stronger the forces of attraction, the higher the melting and the higher the boiling point of that substance.

Substance A has a lower melting point than substance B, because it has weaker forces of attraction holding the particles together.

And we can see here, we've got a diagram of substance A and substance B.

And the arrows have been drawn on which represent the forces of attraction for substance B.

And those forces of attraction are slightly thicker, which is representing that they are stronger than the forces of attraction on A, which are thinner.

So therefore, more energy is going to be needed to overcome the forces of attraction in substance B, which means that it has a higher melting and boiling point, and substance A will therefore have a lower melting and boiling point, because the forces of attraction are weaker.

Let's check our understanding.

True or false.

All substances have the same strength forces of attraction between their particles.

True or false? This is false.

And then justify your answer.

Different substances have different melting points due to different strength forces.

A substance with weak forces between the particles will have a high melting and boiling point.

This is A, so different substances have different melting points due to different strength forces.

B is wrong because a substance with weak forces between the particles will actually have a lower melting and boiling point.

So well done if you recognise that.

Substances that are made of small molecules may look like this.

And we've got a key here, which is showing you forces between the molecules of the pink arrows and covalent bonds between the atoms within the covalent molecule are the blue arrows.

So we can see we've got some small molecules here, and there are forces that exist between those molecules which are shown in pink.

So small molecules have only weak forces between the molecules.

And because of this, they are usually gases or liquids, and they have low melting and boiling points.

We can see that there are strong covalent bonds within the molecule holding the atoms together within the molecule, and they are very, very strong.

So they have strong covalent bonds between the atoms that are not broken during a change of state, for example, in melting.

So small molecules, for example, water, oxygen, nitrogen, carbon dioxide, these all are molecules that have very strong covalent bonds within the molecule holding the atoms together.

But they have weak forces between the molecules which are represented by the pink line on this diagram.

And when you are melting or boiling these small molecules, you are overcoming the weak forces between the molecules, the intermolecular forces, and therefore, small molecules usually have very low melting and boarding points, because they have weak intermolecular forces that don't require much energy to overcome.

Intermolecular forces between small molecules increase with the size of the molecules.

So larger molecules have higher melting and boiling points.

So here if we looked at methane, which is just made up of five atoms within that molecule, so CH4, you can see that the intermolecular forces exist between the molecules, but because it's a small molecule, it's weaker, and therefore, its boiling point is minus 162 degrees.

It doesn't need much energy that overcome those weak intermolecular forces.

Whereas, if we look at propane now, though it's a larger molecule, the intermolecular forces are going to be stronger in comparison to methane.

So therefore, the boiling point will be higher than methane's boiling point, which we can see here.

The boiling point is minus 42 degrees, which is higher than methane's boiling point at minus 162 degrees.

And then if we look at poly(propane), which is an even larger molecule, it's a polymer.

There will be stronger into molecular forces between the molecules again, and this means that there will be a higher melting point in comparison to propane.

And you can see that the larger the molecule, so poly(propane) is the largest molecule.

Its melting point is the highest at 160 degrees Celsius.

Let's check our understanding of that.

So which of the substances below would have the lowest melting point? A, ethanol.

B, sucrose.

Or, C, glucose.

This is going to be A, ethanol, because it is the smallest molecule, so therefore, it has the lowest melting point.

Well done if you got that right.

Ionic compounds and metals have giant lattices, which we can see here on this diagram here, which is showing you an ionic compound.

And giant lattice have bonds formed by electrostatic forces of attraction in all direction, which exist between oppositely charged ions, positive metallic ions, and electrons.

But both ionic compounds and metallic structures have giant lattices, which means they're made up of billions of ions.

Therefore, large amounts of energy are needed to break these many strong bonds that exist.

So they have high melting points and high boiling points.

So this is showing you lithium iodide, which is an ionic compound.

And it's melting point is 446 degrees Celsius.

Giant covalent structures we're going to look at next.

So this image here is showing you Buckminsterfullerene, which sublime at 800 degrees Celsius under a vacuum.

So giant covalent structures are made from atoms that are held together by strong covalent bonds, and it requires large amounts of energy to overcome these strong bonds and to change state.

They are solid at room temperature, and they have very high melting points.

Let's check our understanding.

Select the correct statements.

A, a large amount of energy is needed to overcome strong bonds and change state.

B, a large amount of energy is needed to overcome weak bonds and change state.

C, very high melting and boarding points occur in giant structures as there are lots of strong bonds to break.

And D, very high melting and boarding points occur in giant structures as there are lots of weak bonds to break.

So the correct statements are A and C.

Well done if you've got those right.

Next question, select all types of substance that have high melting and high boiling points.

A, substances with metallic bonding.

B, substances that consist of small molecules.

C, substances that have giant covalent compounds.

And D, substances that have a giant ionic lattice.

So you should have here, A, metallic substances have high melting points.

Giant covalent substances have high melting points, so C.

And also giant ionic substances have high melting points, so D.

Small molecules have weakened molecular forces, so they have low melting and boiling points.

Next question, which melting point below indicates the substance that has the strongest forces between the particles? A, oxygen melting point is minus 218 degrees.

B, water melting point is zero degrees.

C, sulphur melting point is 115 degrees.

And D, poly(vinyl chloride) melting point is 260 degrees.

This is going to be D, because poly(vinyl chloride) has the highest melting point, which suggests that it has the strongest forces between particles.

So fantastic job if you've got that right.

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

And in part one, Lucas has been discussing chemical and physical changes.

Use the choices in the brackets to make his sentences correct.

So Lucas has said, "When a substance changes from a liquid state to a gas state, it is a chemical change or physical change." A physical change often involves a change of state or chemical reaction, for example, boiling.

And in a chemical reaction, particles are not arranged, rearranged, and become chemically bonded to different or the same particles.

So have a go at this, and then press play when you're ready for me to go through the answers.

Let's see how we did.

So in the first sentence, you should have put it is a physical change.

So well done if you got that right.

And the second one, a physical change often involves a change of state, for example, boiling.

And then the final example in a chemical reaction, particles are rearranged, and become chemically bonded to different particles.

Fantastic job if you manage to get those right.

Well done.

Moving on to the second part of task A.

Is this a physical change or a chemical change? And give reasons for your answer.

And then B, is this a physical change or a chemical change? Give reasons for your answer.

So pause the video, and then press play when you're ready for me to feed back.

Let's see how we did.

So 2, A, this is an example of a chemical change.

And we know this because atoms are rearranged, and now bonded to different atoms. And also, sulphur is now bonded to oxygen in sulphur dioxide, which is a new substance.

So well done if you got that right.

Now, 2, B, this is showing you a physical change.

Only a state change from the liquid state to the solid state has occurred.

So this is freezing.

Substance A freezes, i.

e.

it changes to different arrangement of particles, but not chemically bonded to different types of particles.

We haven't formed a new substance, rearranged any atoms, or broken formed any new bonds.

We've just rearranged the way that the atoms are.

And then part three of task A, Laura has been writing about forces of attraction between particles.

Complete the missing words.

If the forces of attraction between particles are, then it takes more energy for a substance to melt or boil.

The stronger the force of attraction between particles, the, the melting point.

So fill it in those blanks.

Let's see how we did.

So if the forces of attraction between particles are stronger, then it takes more energy for a substance to melt or boil.

And the stronger the forces of attraction between particles, the higher the melting point.

Fantastic job if you've got those right.

Well done.

Now, looking at part four of task A, match up the boxes about bonding and melting and boiling points.

We've got ionic substances, metallic substances, giant covalent substances, small covalent substances, and then many strong covalent bonds, strong electrostatic forces of attraction, and weak forces of attraction between molecules.

You're going to match up the boxes on the left to the boxes on the right.

And then the same thing here.

Low amount of energy needed to overcome or break, lots of energy needed to overcome or break.

And then you're going to match those to low melting and boiling temperatures, high melting and boil point temperatures.

So have a go at that, and then press play when you're ready for me to go through the answers.

So here we should have ionic substances going to strong electrostatic forces of attraction, and then lots of energy needed to overcome and break, having a high melting and boiling point.

Metallic substances have strong electrostatic forces of attraction, lots of energy needed to overcome in high melting and boiling temperatures.

Giant covalent structures have many strong covalent bonds with lots of energy needed to overcome and break, and have high melting and boiling temperatures.

Small covalent substances have weak forces of attraction between molecules, a low amount of energy needed to overcome and break, and a low melting and boring point temperatures.

So well done if you manage to correctly go through each one of those substances.

Well done.

Fantastic job so far.

Let's move on to the second part of our lesson, which is predicting states.

If you know the melting and boiling point of a substance, you can predict what state of matter, it will exist as at a specific temperature.

It can be helpful to use a number line to help you visualise this.

This line here is representing our number line.

So we've got the temperature in degree Celsius, if that is 0 degrees Celsius, and that is 100 degrees Celsius, and then that it directly within the middle would be 50 degrees Celsius.

The melting point of water is at 0 degrees and the boiling point of water is at 100 degrees.

So therefore, anything below the zero degrees is going to be a solid state.

Anything between 0 and 100 degrees is gonna be the liquid state, and 100 degrees and above is going to be the gas state.

So marking the melting and the boarding point on a number line helps us to work out what state a substance is going to be at.

Ethanol has a melting point of minus 114 degrees Celsius and a boiling point of 78 degrees Celsius.

In what state of matter is ethanol at minus 120 degrees Celsius.

So if we draw a number line and we're going to put on 0 degrees roughly in the middle, minus 114 is showing you the melting point, and 78 degrees is showing you the boiling point.

So below minus 114 degrees is a solid state, in between, minus 114 and 78 is the liquid state, and 78 degrees and above is the gas state.

So in what state of matter is ethanol at minus 120 degrees going to be below minus 114, so ethanol will be a solid at minus 120 degrees Celsius.

If you have a go now, at the next example, methanol has a melting point of minus 98 degrees Celsius and a boiling point of 65 degrees Celsius.

What state of matter is the methanol at 25 degrees Celsius? So you draw a number line, mark on the melting and boiling point, and then predict the state at 25 degrees.

So you should have drawn your number line with 0 degrees there minus 98 degrees written on, and 65 degrees, and then the state.

So we've got solid liquid, and gas.

And what state of matter is the methanol 25 degrees, it's going to be below 65 degrees, so it's going to be in the liquid state.

So fantastic job if you managed to get that right.

Well done.

So methanol is in the liquid state at 25 degrees.

So we're now ready to move on to task B.

And Sophia has been discussing state changes, and you need to correct her sentences.

So there's four statements she's made here, and you need to correct each one of those statements.

So pause the video and give it your best go, and then press play when you are ready for me to go through the answers.

Let's see how we did.

So minus 113 degrees Celsius is a higher temperature than minus 117 degrees Celsius.

A substance is in the liquid state when it is above the melting point, but below the boiling point.

A substance that boils at minus 100 degrees Celsius will be in the gas state at room temperature of 25 degrees Celsius.

And the substances in the solid state below the melting point.

A fantastic job if you manage to get those right.

Well done.

And in part two of task B, you need to predict the state of matter of the substances at the different temperatures.

So you've been given the substance, the melting, and the boiling point, and then you need to say what state of matter they will be at at those different temperatures there.

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

So water at minus 200 degrees, it will be solid, because that's below its melting point.

At 0 degrees, it will be a solid, as well.

At 50 degrees, it will be a liquid, because that is below its boiling point, but higher than its melting point.

And it will be gas at 100 and also 1,500 degrees Celsius.

Now, the gold, it's solid at minus 200, solid at 0 degrees, solid at 50 degrees, solid at 100 degrees, and a liquid at 1,500 degrees, because that is higher than its melting point.

For oxygen, it's a liquid at minus 200 degrees, and then it's a gas at all the other temperatures.

Nitrogen is a liquid at minus 200 degrees, and it's a gas at all the other temperatures.

Silicon dioxide is a solid at minus 200 degrees and 0 degrees, and it's also a solid at all the other temperatures.

And potassium bromide is a solid at all the temperatures other than 1,500 degrees where it is a gas, because it will have boiled at 1,435 degrees.

So fantastic job if you've got those right.

Well done.

Now, part three of task B water is a small molecule using information from your completed table, suggest other substances that might also be small molecules, and explain why you chose those substances.

So give this your best go and then press play when you are ready for me to go through the answers.

Let's see how we did.

So oxygen, nitrogen should have been the ones that you picked.

They are the small molecules, because they have low melting and boring points, not so much energy as needed to overcome the intermolecular forces.

Gold, silicon dioxide, and potassium bromide are not small molecules, because they have high melting and boiling points.

So cannot be small molecules, because too much energy is needed to break the bonds in these substances to change states.

Really fantastic job if you manage to get that right.

If you want to pause the video to add in any extra detail from this task, then please do.

But I'm going now to summarise everything that we've learned in today's lesson.

So in today's lesson, we've been predicting states of matter, and we started off by saying, there are changes in arrangement, movement, and energy of particles during states changes.

And there are two types of change, physical and chemical, and these can be explained in terms of the particle model.

And we said that physical changes involve no breaking of bonds.

It's just that the particles are rearranged, and they stay the same substance, whereas chemical changes involve bonds being broken, new bonds being formed, and a new substance being formed.

The physical state of a substance can be predicted at specific temperatures.

And forces of attraction between particles have a role in determining the amount of energy needed for a state change.

So weak forces of attraction usually mean a lower melting and boiling point and stronger forces of attraction lead to a higher melting and boiling point.

I hope you've enjoyed today's lesson.

I have.

And I look forward to seeing you next time.