Lesson video

Hello there.

I'm Mr. Forbes, and welcome to this lesson from the Energy of Moving Particles unit.

This lesson's called "Heating Different Substances," and in it we'll look at the energy changes involved when an object is heated or is allowed to cool.

By the end of this lesson, you're going to be able to describe how a materials specific heat capacity is a description of how easily it's heated or how much energy it transfers as it cools.

Here are the key words that'll help you during this lesson.

The first is temperature, and that's the measurement of how hot a substance is.

And it's related to how much kinetic energy the individual particles of that material have.

Then we have the specific heat capacity, which is what the focus of this lesson is, and that's the change of internal energy when the temperature of one kilogramme of a material changes by one degree Celsius.

Next we have internal energy, and that's the sum of the kinetic energy and the potential energy of all the particles that a substance is made of.

Then kinetic energy, that's the energy a moving object has.

And finally, potential energy, and that's the energy that an object has because of its position and the forces that are acting on it.

You can return to this slide at any point during the lesson.

The lesson's in three parts, and in the first part we'll be looking at all the factors that affect the size of thermal energy stores.

In the second part of the lesson, we'll be putting those ideas together, form the idea of a specific heat capacity of material.

And in the final one, we'll look at the details of what internal energy is and the changes that can happen.

So let's start by looking at thermal energy stores.

If you need to cool down a piece of metal quickly, one of the ways of doing that is to put it into some cold water, and that's what a blacksmith does.

So if you've got a hot piece of metal, like that piece of iron at 1,600 degrees Celsius, then if you want to cool it, you can plunge it into some cold water.

The energy is transferred by thermal conduction from the metal into the water, and so the metal loses energy, and the water gains energy, and that means that the temperature of the metal decreases, and the temperature of the water increases.

And that process will continue until the metal and the water are at the same temperature.

They've reached thermal equilibrium at the same temperature.

Now, that water's obviously going to get hotter when you put the metal into it, and we are gonna look at the factors that affect how much that temperature of the water changes.

So the initial temperature of the iron is the first factor we'll look at, and, obviously, that's gonna have an effect on the change in temperature in the water.

So we've got two pieces of iron here.

We've got an equal mass.

One of them starts at 1,000 degrees Celsius, and the other 1,500, and they're gonna put them into an equal mass of water that starts at the same temperature, 20 degrees Celsius.

So if I drop the first one in, you can see that the water temperature is increased to 50 degrees Celsius.

So the temperature increase in water is 30 degrees Celsius.

And I dropped the hotter piece of metal in, and the water temperature is increased, but it's increased to a greater amount.

It's now 65 degrees Celsius.

So the water temperature has increased by 45 degrees Celsius there.

So the higher the temperature of the metal at the start, the more energy it could transfer to the water, more energy it could pass into the water, and that's caused a greater increase in the temperature of the water there.

Let's see if you understood the idea.

I've got three beakers.

They've got one kilogramme of water each, and they all start at the same temperature, 20 degrees Celsius and hot pieces of copper metal, which have equal mass, are dropped into the beakers and the new water temperature is shown.

So you can see the new water temperatures there.

We've got 28 degrees, 38 degrees, 25 degrees.

Which piece of copper had the highest starting temperature before it was dropped into the water? So pause the video, make a decision, and restart please.

Welcome back.

The answer to that was B.

That piece of copper transferred more energy into the water.

The water heated up more.

Its temperature increased the most, so that copper must have had the most energy, so it must have been at the highest temperature.

Well done if you got that.

Now, let's look at a second factor, and that factor is the mass of the piece of metal.

So I've got two pieces of metal here, again, both pieces of iron, both are starting at the same temperature, 1,000 degrees, but one piece has got twice the mass of the other.

And again, I've got equal masses of water starting at the same temperature again, and I'm gonna put the pieces of metal in.

So if I drop the first piece of metal, the smaller piece of metal into the water, the temperature's gone up to 30 degrees Celsius.

So it's increased by 10 degrees there.

If I drop the second piece of metal in, so remember this had a greater mass, then the temperature's gone up to 40.

It's a greater increase in temperature there.

The temperature increase of the water was 20 degrees Celsius.

So the greater the mass of the metal, the more energy it can transfer to the water and heat it up.

Let's check if you understood that idea.

So I've got three beakers again, one kilogramme of water in each, each at the same temperature, 20 degrees, hot pieces of copper at the same temperature, but with different masses are dropped into the beaker.

Which thermometer will show the smallest temperature increase when I do that? And you can see the masses of the pieces of copper are shown in the diagrams. So pause the video, make your decision, and restart please.

Welcome back.

Hopefully, you selected A.

That's gonna have the smallest temperature increase.

There was the smallest mass of copper there, only 20 grammes.

That's gonna have the least energy it can transfer to the water as it cooled down.

So well done if you selected that one? Now, let's look at the third and final factor that affects the amount of energy the metal can transfer to the water, and that's the type of metal.

So in this example I've got two different metals.

We've got aluminium and iron.

Both have got an equal mass, and both are starting at the same temperature of 600 degrees Celsius there.

And I'm dropping them both into samples of water of equal mass and at the same starting temperature.

So if I drop the aluminium in, you can see the temperature's increased to 30 degrees Celsius.

So that's a temperature increase of 10 degrees.

And if I drop the iron in, that goes to 25 degrees Celsius.

So that's only increased by five degrees.

So some materials have more energy they can provide to the water when at the same temperature.

So the aluminium has provided more energy to the water than the iron was able to, even though they started with the same mass and at the same temperature.

So now, it's time to check you understood that final example.

I've got three beakers of water again, one kilogramme in each, each starting at 20 degrees Celsius, and I've got 100 gramme pieces of three different metals all starting at the same temperature, 500 degrees Celsius, and it dropped into the beakers.

And the new temperature of the water is shown in the diagram.

You can see there are different temperatures there.

Which piece of metal was originally storing the most energy it could provide to the water? So pause the video, make a selection, and restart please.

Welcome back.

Hopefully, you selected the last of them, option C there.

That water temperature has increased the most.

It's at 45 degrees Celsius, the largest temperature rise.

So that metal must have provided it with the most energy.

So well done if you selected that.

So as we've seen in those examples, the energy stored by a sample of material depends on three different factors.

First of all, the temperature.

The higher the temperature, the more energy is stored by that material.

The second is the mass, and the greater the mass, the more energy is stored by that material as well.

And finally, the type of material.

Some materials will store more energy than others for the same mass and the same temperature.

Okay, let's see if you can combine all those factors together.

An example.

Which of the objects is storing the most energy in its thermal store here? So I've got three objects, and you can see we've got an iron cube, an ion sphere, and an iron in cylinder.

We've got the masses and the temperature there as well.

So which of those objects is storing the most energy in external store? Pause the video, make a decision, and restart please.

Welcome back.

Well the answer to that was C, They're equal.

They're all the same material, they're all the same mass, and they're all the same temperature.

So the factors are all the same for them.

So they're going to be storing the same amount of energy in their thermal stores.

Well done, if you've got that.

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

You're given three different rocks with a of 100 grammes.

So three rocks, 100 grammes each.

I would like you to write out a simple plan to find out which of them has the greatest specific heat capacity, which one can store the most energy per kilogramme per degree Celsius.

Your plan should include an equipment list, a diagram, a simple method, and an explanation about how the results will show which one has the highest specific capacity, which one could store the most energy per kilogramme per degree Celsius.

So, pause the video, write out your plans, and restart please.

Welcome back.

And here's the answer to that task.

So I've got my equipment list here.

I've got my rock samples, some tongs to handle 'em 'cause they're gonna be hot, a beaker of hot water at constant temperature, and that's to heat them up to a high temperature.

Then, I've got beaker with a 200 centimetre cube of water and a thermometer.

What I'm doing is I'm gonna place each of those stones into some hot water until they reach the same starting high temperature.

Then, we're gonna use the tongs to transfer them to the cooler water.

And then, we're gonna measure the temperature increase of that cool water.

And the rock that causes the greatest increase in temperature is going to have the greatest specific heat capacity.

It's able to transfer most energy to the water when it starts at the same temperature.

Well done if you've got that.

Now, it's time for the second part of the lesson, and in it, we're going to look at the specific heat capacity of material, and that's related to the amount of energy it can store.

If we place a piece of hot metal into some ice, it will melt some of the ice as the metal cools, and the amount of ice that it can melt will depend on how much energy that material or that metal was able to transfer to the ice or how much energy it was storing originally.

So let's say I've got a piece of metal, it's at 200 degrees Celsius, and I place it in a beaker of ice.

What's going to happen is some of that ice is going to melt, and at the same time, because energy's being transferred to the ice to melt it, the temperature of the metal block is going to decrease.

So it's decreased down there to 100 degrees Celsius, and that's going to continue until eventually the metal isn't able to transfer energy to the ice anymore.

So a question for you.

Imagine you've got two identical copper blocks.

They've got the same mass, and they're at the same temperature.

Which block will melt the most ice in five minutes? So we've got the blocks there, X and Y.

Is it block X, block Y, or both blocks able to melt the same amount of ice? So pause the video, make your selection, and restart please.

Welcome back.

Hopefully you selected C.

Both blocks are identical at the same temperature, at the same metal, the same mass, and therefore, they're going to be able to transfer the same amount of energy to the ice and that means they're gonna be able to melt the same amount of ice.

Well done, if you've got that.

As I mentioned earlier in the lesson, different materials can store different amounts of energy when their temperatures increased, and the specific heat capacity of a material is defined as the energy required to raise the temperature of one kilogramme of that material by one degree Celsius.

So if I've got a one kilogramme sample of a material with a high specific heat capacity, it's going to store more energy per degree Celsius than one with a lower specific heat capacity, and that means it's gonna be able to transfer more energies to the surroundings when it's allowed to cool because it's got more energy stored in it in the first place.

Okay, then I've got two metal blocks here, and I've got the same mass in the same temperature.

They're both starting at 100 degrees celsius.

One block is lead, and that's got a specific heat capacity of 160 joules per kilogramme per degree Celsius.

The other block is copper, and that's got a different specific heat capacity.

It's got a higher specific heat capacity of 385 joules per kilogramme, per degrees Celsius.

Which one of those blocks is going to be able to melt the most ice in five minutes.

So pause the video, read through the information, make a selection, and then restart please.

Okay, welcome back.

Hopefully, you selected the copper block.

The copper block has a greater specific heat capacity.

That means it's storing more energy per degree Celsius per kilogramme.

So it's able to transfer more energy to the ice as it cools down.

So you've seen two different materials with two different specific heat capacities.

There are many other materials, and they've all got different specific heat capacities.

I've got some example values here for you.

Here's a set of metals, and as you can see, different metals will store different amounts of energy per kilogramme per degree Celsius of their temperature.

So we've got aluminium, which has got the highest in this table.

That will store 921 joules per kilogramme per degree Celsius, down to gold, which has got a much lower specific heat capacity there, only 125.

We can compare that with some non-metals.

So we've got some non-metals here, and as you can see, water has got a particularly high specific heat capacity.

It's very difficult to change the temperature water.

It takes a large energy change to do that.

Wax, again, has got high specific heat capacity.

Even air's got higher specific heat capacity than glass.

So you can see that actually metals have got lower specific heat capacities than most non-metals.

Let's check your understanding of specific heat capacity.

Have got equal masses of milk and water, and heated the same way for five minutes.

The temperature of the milk is increasing more than the temperature of the water.

So which two of these statements are correct? So pause the video, read through the statements, select the two correct ones, and then restart please.

Welcome back.

Hopefully, you selected the answers C and D because of heated them for the same amount of time in the same way, I've given them equal amounts of energy, and water has a higher specific heat capacity than milk because its temperature has increased the least for the same amount of energy provided to it.

Well done, if you selected those two.

Okay, we've now reached the second task of the lesson, and it's all about specific heat capacity.

I've got a table showing specific heat capacities of some metals and water there.

So you've got that list, aluminium, iron, copper, gold, and water, and then I'm gonna be using electrical heaters to heat 100-gram samples, so equal mass samples of each metal, for the same length of time.

I'd like you to decide which metal will have the greatest temperature increase, and then which will have the smallest temperature increase.

Then the second question.

I've got 100 gramme samples of each metal, and I heat them all to 300 degrees Celsius and then drop them into identical containers of cold water.

I'd like you to state which metal will heat the water up the most, and explain why.

So pause the video, work out your answers to those questions, and restart please.

Welcome back.

Well for question one, the gold will have the greatest temperature increase because it's got the lowest specific heat capacity.

It takes the least amount of energy to heat one kilogramme of it by one to be Celsius, and the aluminium will have the smallest temperature increase out the metals 'cause it's got the highest specific heat capacity out of the metals.

For question two, the water will be heated most by the aluminium because it will have more energy stored in it than the other metals, and so that's got the highest specific heat capacity.

It's storing most energy.

Well done, if you've got answers to those two.

And now it's time to move on to the final part of the lesson.

And in it, we're going to explain why different materials have different specific heat capacities by looking at the internal energy of the material.

As we've seen already, it's harder to increase the temperature of some materials than others, and that's because they've got different specific heat capacities.

So for example, the specific heat capacity of aluminium is 921 joules per kilogramme per degree Celsius.

But the specific heat capacity of iron is only 460 joules per kilogramme per degree Celsius.

You need more than twice as much energy to increase the temperature of aluminium compared to the temperature of iron.

And the differences in those specific heat capacities are due to the different masses of the particles that make up the material and the forces between those particles.

So we're going to look at those.

So as I mentioned, one of the reasons for different specific heat capacities is the differences in mass of the particles that make up the material.

So I've got particles with less mass here, and particles with greater mass here.

They're larger particles, and we should already know that the kinetic energy of the particles depends upon the mass.

The greater the mass of the particles, the more energy is required to make them increase their speed.

So if we transfer the same amount of energy to these two materials, the energy that I've provided is the same, but the speed of the particles with more mass is going to increase less than the speed of the particles with less mass.

So the vibrations are gonna change differently.

The temperature increase per joule for the smaller particles, the lower mass particles, is going to be greater because they're gonna be moving faster for the energy provided to them.

Whereas the temperature increase of the material with the larger or more massive particles is going to be less because the particles are more massive, and the velocity, the speed, doesn't increase as much, and the speed is what determines the temperature.

Let's check if you understood the idea, and which of these substances will the speed of the vibration of the particle increase the most when the same amount of energy is transferred to each of them? So I've got three materials there with different masses of particles, and their masses are represented by the sizes.

So pause the video, make a decision, and restart please.

Welcome back.

Hopefully, you selected C.

They're the smallest mass particles.

So those speed is going to increase the most per joule provided to it.

So well done, if you got that.

So the second factor that affects the internal energy in a specific heat capacity is to do with the attractive and repulsive forces between the particles inside the material.

So if you imagine two particles in the material, if those particles are too close together, forces between them, the electrostatic forces, push those particles apart slightly.

So it's repulsive at very short distances.

But if you try to stretch the material, those electrostatic forces start to pull back the material.

They pull the particles back together.

So you can think of those forces as acting a little bit like a spring.

When the particles are too close together, the spring will push the particles apart, and when the particles are too far apart, that soft spring will pull the particles back together.

The strength of the forces between the particles in different materials is different and not all the same at all.

So some materials have strong forces between the particles, and I can show that in my diagrams. For example, a thicker spring acting between them because thicker springs will give bigger forces.

Some particles have weaker forces between them.

I can show that by drawing a thinner spring between them.

Stronger forces will make it more difficult for the particles to vibrate past each other when you transfer energy to the material.

So the materials with the strong forces are going to be harder to increase the temperature of.

So I've got an example here.

Here, in these sets of diagrams, I have represented the forces by springs, and I've shown them as different thicknesses depending on the strength.

In which substance will the vibrational speed of the particles increase the least when they're heated by the same amount, when they're given the same amount of energy? So pause the video, make a selection, and restart please.

Welcome back.

Hopefully, you selected A.

That's got the largest forces between the particles represented there by the thicker, bolder springs.

And so the speed increase of those particles is going to be the least out the set.

So well done, if you selected those.

When you stretch a spring, you do work on it.

You do mechanical work on a physical spring, and it stores energy.

And something similar happens in materials as well.

So I've got a spring here.

I put forces on it to cause it to stretch.

And I put larger forces on it to cause it to stretch a bit more, and even larger forces to cause it to stretch the most.

So the size of the force that I need to use to stretch that spring increases as the length of the spring increases.

And that means that the potential energy stored by the spring is going to increase the more it's stretched.

So comparing that to particle behaviour, work is also done when you are pulling apart particles.

The further apart you pull them, the more work is done on the material.

So I've got some energy stored in a bond here.

As I stretch those particles further apart, I store more energy in them.

And as I stretch 'em even further, even more energy is stored between the bonds in those particles, the electromagnetic forces.

So the potential energy in the bonds is increasing when the particles are further apart.

And that means that the temperature doesn't increase as much for every joules of energy transferred when those bonds are stronger.

So in this diagram, the forces between the particles are shown by those springs again, and I'd like to know in which diagram is the most potential energy being stored by the pair of particles.

So pause the video, make your decision, and restart please.

Welcome back.

Hopefully, you selected A And it's A because that bond, that spring, has been stretched the most, so there's most potential energy stored in it 'cause the particles are furthest the part.

Well done, if you selected that.

So now we know the nature of the internal energy of an object.

The internal energy of an object is the sum of all of the kinetic energy of the vibrating particles and also the potential energy of the particles due to their positions in the bonds or the electromagnetic forces between them.

If we heat an object, we are going to be increasing the internal energy of that object.

What that does is it can increase the internal, sorry, the kinetic energy of the particles.

And that means that the temperature of the object goes up because temperature is related to the movement or the vibration of the particles in it.

And it can also cause changes to the potential energy of the particles.

Well, that doesn't increase the temperature because the particles aren't vibrating anymore quickly.

But it could cause a change of state.

It could cause the material to melt.

So it can have changes in internal energy due to kinetic energy changes or potential energy changes, or a combination of both if I heat the object enough.

Okay, a question based on that for you.

I've got a cube of ice, it's at zero degrees Celsius, and it melts from liquid water, which is also at zero degrees Celsius.

Which of those statements are correct? So I'd like you to choose the two correct statements for me please.

Pause the video, make your selections, and restart.

Okay, welcome back.

Hopefully, you selected these two.

The internal energy of the water has increased.

Its internal energy has increased there, and that's because the potential energy of the water particles has increased as they've separated further.

The temperature hasn't changed, so the kinetic energy of the water particles hasn't increased.

So B is wrong.

And there has been a change in energy because the material has melted.

It's changed it's state.

So well done, if you selected A and C.

Okay, we've reached the end of the lesson now, and what I'd like you to do is to read through these statements and fill in the blanks please.

So I've left blanks in each of those statements.

I'd like you to fill them in at one word per blank space please.

So pause the video, fill in the blanks, and restart when you're done.

And welcome back.

And here's my answers to that.

The internal energy of a material is the sum of the kinetic energy and the potential energy of the particles within it.

The kinetic energy of the particles in a material depends upon their mass and their speed of vibration.

The greater the mass of the particles, the more energy is required to increase their average speed.

The potential energy of the particles is stored by the bonds between them.

And when the particles are further apart, more energy is stored by the bonds between them.

Well done, if you've got those answers.

Okay, we've reached the end of the lesson, and here's a summary of all of that information we've covered.

The internal energy of a material is the sum of the kinetic energy and the potential energy of all the particles within it.

Heating increases the internal energy, which can increase the average kinetic energy in the particles, increasing particle speed and the temperature of the material, or increase the potential energy in the bonds between the particles, which does not increase the temperature.

The energy stored by material depends upon its mass, temperature, and its specific heat capacity.

And the specific heat capacity of a material is the energy required to raise the temperature of a one kilogramme sample of material by one degree Celsius.

Well done for reaching the end of this lesson.

I'll see you in the next one.