GCSE Physics - Specific Latent Heat #29

Summary

This video explores the concept of specific latent heat (SLH), which is the energy required to change a substance's state without altering its temperature. It explains how SLH differs from the typical increase in temperature when heating a substance, highlighting the processes of melting, freezing, evaporation, and condensation. The video uses the example of heating one kilo of ice to water vapor, detailing the specific latent heat of fusion and vaporization for water, and provides the formula for calculating energy changes during state transitions. It concludes with a practical application question involving boiling water.

Takeaways

• 🔥 The concept of specific latent heat is introduced, which is the energy required to change a substance's state without changing its temperature.
• 🌡️ Temperature is a measure of the average internal energy of particles in a substance, but it doesn't increase during state changes due to energy being used to break inter-particle forces.
• 📊 The graph of temperature change over time for a substance is not a straight line, especially during phase transitions where energy input is used to change states, not increase temperature.
• ❄️ The specific latent heat of fusion is the energy required to change a substance from a solid to a liquid, such as ice melting into water.
• 🌫️ The specific latent heat of vaporization is the energy required for a substance to change from a liquid to a gas, like water boiling into vapor.
• 💧 For water, the specific latent heat of fusion is 334,000 joules per kilogram, which is the energy needed to melt ice at 0 degrees Celsius.
• 🌬️ The specific latent heat of vaporization for water is 2,260,000 joules per kilogram, necessary to convert liquid water into water vapor at 100 degrees Celsius.
• 🔄 The same principles apply in reverse during cooling, with energy being released during state changes, which keeps the temperature constant.
• ⚖️ The specific latent heat (SLH) is defined as the energy required to change one kilogram of a substance from one state to another without a temperature change.
• 📘 The formula for calculating specific latent heat is the mass of the substance multiplied by the specific latent heat value.
• 📝 An example calculation is provided to demonstrate how to use the specific latent heat values to determine the energy required to boil a certain mass of water.

Q & A

What is specific latent heat?

Specific latent heat is the amount of energy required to change the state of a substance while the temperature remains constant. It is used to break or form bonds between particles during phase changes such as melting, freezing, vaporization, or condensation.

Why does the temperature of a substance remain constant during a phase change?

The temperature remains constant during a phase change because the energy supplied is used to overcome the forces between particles rather than to increase their kinetic energy, which is what typically raises temperature.

What are the two types of specific latent heat mentioned in the script?

The two types of specific latent heat are the specific latent heat of fusion, which is the energy change when a substance changes between a solid and a liquid, and the specific latent heat of vaporization, which is the energy change when a substance changes between a liquid and a gas.

What is the specific latent heat of fusion for water?

The specific latent heat of fusion for water is 334,000 joules per kilogram, which is the energy required to change ice at 0 degrees Celsius to liquid water without changing its temperature.

What is the specific latent heat of vaporization for water?

The specific latent heat of vaporization for water is 2,260,000 joules per kilogram, which is the energy required to change liquid water at 100 degrees Celsius to water vapor without changing its temperature.

How is the specific latent heat used in calculations?

The specific latent heat is used in calculations to determine the amount of energy required or released during a phase change. It is calculated using the formula: Energy = Mass of the substance × Specific latent heat.

What happens to the temperature of a substance when it is heated from a solid state to a gaseous state, passing through a liquid state?

As the substance is heated from a solid to a liquid state, the temperature remains constant at the melting point until all the substance has melted. Then, as it is heated from a liquid to a gas, the temperature remains constant at the boiling point until all the substance has vaporized.

What is the difference between the energy required for a substance to melt and the energy released when it freezes?

The energy required for a substance to melt is the specific latent heat of fusion, which is absorbed to break the bonds between particles. Conversely, the energy released when a substance freezes is the same amount of energy, but it is released as the substance changes from a liquid to a solid state.

How can you calculate the energy required to boil a certain amount of water?

To calculate the energy required to boil water, you multiply the mass of the water by the specific latent heat of vaporization. For example, to boil 2.5 kilograms of water, you would use the formula: 2.5 kg × 2,260,000 J/kg = 5,650,000 J or 5,650 kilojoules.

Why is it important to understand specific latent heat in the context of phase changes?

Understanding specific latent heat is important because it helps explain why the temperature of a substance does not change during phase changes, despite continuous energy input or output. It is also crucial for various applications in science and engineering, such as refrigeration, heating, and thermal energy storage.

What is the significance of the graph in the script that shows how the temperature of a substance changes with time as it is heated?

The graph is significant because it illustrates the non-linear relationship between temperature and heat input during phase changes. It shows that the temperature plateaus at the melting and boiling points, indicating that the energy is being used for phase change rather than increasing temperature.

Outlines

00:00

🔥 Understanding Specific Latent Heat

This paragraph introduces the concept of specific latent heat and its role in phase changes. It explains that while heating or cooling a substance generally increases or decreases its temperature, this is not the case during phase transitions. The energy supplied during these changes is used to overcome intermolecular forces rather than increasing the temperature. The video script uses a graph to illustrate this point, showing a plateau in temperature during melting or boiling. The specific latent heat is defined as the energy required to change one kilogram of a substance from one state to another without a change in temperature, and it varies depending on the substance and its quantity.

05:00

🌡️ Calculating with Specific Latent Heat

The second paragraph delves into the practical application of specific latent heat, focusing on the two types: the specific latent heat of vaporization and the specific latent heat of fusion. It uses the example of heating one kilogram of water from -50°C as solid ice to 150°C as gaseous vapor, detailing the energy changes at the melting and boiling points. The specific latent heat of fusion for water is given as 334,000 joules per kilogram, and the specific latent heat of vaporization as 2,260,000 joules. The paragraph also addresses the reverse process of cooling and the energy released during phase changes. It concludes with a formula for calculating specific latent heat and an example calculation for boiling 2.5 kilograms of water, emphasizing that the exact values will be provided in an exam setting.

Keywords

💡Specific Latent Heat

Specific Latent Heat (SLH) is the amount of energy required to change a substance's state without changing its temperature. It is a key concept in the video, which discusses how energy is absorbed or released during phase transitions such as melting and boiling. The video uses SLH to explain the energy changes during the heating and cooling processes of a substance, particularly water, and how these changes are quantified in joules per kilogram.

💡Kinetic Energy

Kinetic energy is the energy that a substance's particles possess due to their motion. In the video, it is mentioned that as a substance is heated, the particles gain energy, which increases their kinetic energy and, consequently, the substance's internal energy. This concept is foundational to understanding how temperature changes with the application of heat.

💡Internal Energy

Internal energy is the total energy contained within a system, which includes both kinetic and potential energy of its particles. The video explains that as a substance's particles gain kinetic energy, their internal energy—and thus the substance's temperature—increases. However, during phase changes, the energy input is used to overcome intermolecular forces rather than increasing internal energy, keeping the temperature constant.

💡Temperature

Temperature is a measure of the average kinetic energy of the particles in a substance. The video emphasizes that while heating typically increases a substance's temperature due to increased particle kinetic energy, this does not occur during phase changes because the energy is used for breaking intermolecular bonds instead.

💡Phase Change

A phase change refers to the transition of a substance from one state of matter to another, such as from solid to liquid or liquid to gas. The video script discusses how phase changes, such as melting and boiling, involve energy that does not increase temperature but is used to alter the structure of the substance.

💡Melting Point

The melting point is the temperature at which a solid turns into a liquid. In the context of the video, it is the point during heating where the substance begins to change state, and the energy supplied is used to break the bonds between particles, not to increase temperature.

💡Boiling Point

The boiling point is the temperature at which a liquid turns into a gas. The video uses the boiling point to illustrate another instance where energy input is used to change the state of a substance, in this case, from liquid to gas, without changing its temperature.

💡Specific Latent Heat of Fusion

Specific Latent Heat of Fusion is the energy required to change a substance from a solid to a liquid state at its melting point. The video provides the example of water, where this value is 334,000 joules per kilogram, illustrating how this energy is used to initiate the melting process without a temperature rise.

💡Specific Latent Heat of Vaporization

Specific Latent Heat of Vaporization is the energy required to change a substance from a liquid to a gas state at its boiling point. The video script mentions that for water, this value is 2,260,000 joules per kilogram, which is the energy needed for water to boil and turn into vapor.

💡Energy Calculation

Energy calculation in the context of the video involves using the specific latent heat values in mathematical equations to determine the amount of energy required or released during phase changes. The video provides an example calculation for boiling 2.5 kilograms of water, demonstrating how to use the specific latent heat of vaporization in such calculations.

💡Substance

In the video, 'substance' refers to any material that can undergo a phase change. The script discusses how different substances have different specific latent heat values, which are crucial for understanding and calculating energy changes during phase transitions.

Highlights

The concept of specific latent heat is introduced and its application in calculations is explained.

As substances are heated, their particles gain kinetic energy, increasing internal energy and temperature.

An exception to the rule of temperature increase with heating occurs during state changes.

A graph illustrates the non-linear temperature change of a substance during heating due to state changes.

Energy provided during state change is used to break inter-particle forces, not to increase temperature.

The principle of constant temperature during state change also applies to cooling processes.

The specific amount of energy required for state change without temperature change is called latent heat.

Latent heat depends on the type of substance and the amount, leading to the concept of specific latent heat (SLH).

SLH is defined as the energy required to change one kilo of a substance from one state to another without changing its temperature.

Two types of specific latent heat are identified: of vaporization and of fusion.

The specific latent heat of fusion is the energy change when a substance changes from solid to liquid.

The specific latent heat of vaporization is the energy change when a substance changes from liquid to gas.

An example demonstrates heating one kilo of ice to water vapor, highlighting the role of specific latent heat of fusion and vaporization.

The specific latent heat of fusion for water is 334,000 joules per kilo.

The specific latent heat of vaporization for water is 2,260,000 joules per kilo.

Cooling a substance involves the release of energy during state change, as explained by specific latent heat.

The equation for specific latent heat is presented, showing its calculation as mass times specific latent heat.

A practical example calculates the energy required to boil 2.5 kilos of water using specific latent heat of vaporization.

The video concludes with an encouragement for viewers to like and subscribe for more educational content.

Transcripts

in today's video we're going to look at

the concept of specific latent heat

and see how to use it in calculations

we saw in the last video that as we heat

up a substance

the particles gain energy in their

kinetic energy store

and this increases their internal energy

we also saw that temperature is just a

measure of the average internal energy

of all the particles in a substance

so as we heat objects and the internal

energy of their particles increases

the object's temperature increases as

well

the whole point of this video though

is that there is an exception to this

rule

and that's when there's a change in

states

if you take a look at this graph which

shows how the temperature of a substance

changes with time as we heat it

you can see that it's not a straight

line like you might expect

this is because when the substance is

changing state

so at the melting point or the boiling

point

the energy that we're providing is being

used to weaken or break the forces

holding the particles together

rather than increasing the particle's

internal energy

and remember that the temperature is

just a measure of the average internal

energy of the particles

so in this case the overall temperature

won't change in these regions

until all of the substance has changed

states

the same principle applies if we look at

a similar graph for cooling a substance

this time though the state change

involves the formation of new bonds

between particles which releases energy

and so counteracts the cooling

and this is what keeps the temperature

constant during the changing state

now the exact amount of energy that's

required to change the state of the

substance while the temperature remains

the same

is known as the latent heat and it

depends on two things

the type of substance that we have

and the amount of that substance

to standardize these values though we

use the term specific latent heat or slh

which we can define as the energy

required to change one kilo of a

particular substance

from one state to another without

changing its temperature

and for cooling the specific latent heat

would be the amount of energy released

by changing states

now there are actually two types of

specific latent heat

one is the specific latent heat of

vaporization

which is the energy change when a

substance changes between a liquid and a

gas

so either evaporates or condenses

the other one is the specific latent

heat of fusion

which is the energy change when a

substance changes between a solid and a

liquid

so either melts or freezes

to see how all this works let's imagine

that we had one kilo of water

and that we heated it all the way from

minus 50 degrees celsius where it was

solid ice

to 150 degrees celsius where it was

gaseous water vapor

as we heat our one kilo of ice

as particles all gain internal energy

and so its temperature increases

however once we reach zero degrees the

ice starts to melt

and because all the heat energy that

we're supplying is being used to break

the forces between the particles

the overall temperature stays the same

the energy required for this stage is

the specific latent heat of fusion

and in the case of water this is 334 000

joules per kilo

once this much energy has been provided

though and the ice has all melted into

liquid water then the temperature will

continue to increase

all the way to 100 degrees where the

same process happens again

this time though the energy required is

the specific latent heat of vaporization

which is two million two hundred sixty

thousand

and once the water has all boiled into

water vapor its temperature continues to

increase like normal

bear in mind that you don't need to

memorize these figures they'll be given

to you an exam if you needed them

as we said earlier if we were to cool

our water the same concepts would apply

but the amount of energy that we

mentioned for the specific latent heat

of vaporization and the specific latent

heat of fusion would be the amounts of

energy released rather than required at

each stage

the last thing we need to look at is the

equation for specific latent heat

which says that the energy that's

required or released

is equal to the mass of the substance

times the specific latent heat

you can also use this formula triangular

that's easier

so a typical question could be something

like

how much energy is required to

completely boil 2.5 kilos of water at

100 degrees celsius

use the relevant data from the table

well as we're boiling the water

we're going to need to use the specific

latent heat for vaporization value as

that's the one that refers to boiling

so we just do two point five times two

million two hundred sixty thousand

which gives us five million six hundred

and fifty thousand joules or 5 650

kilojoules

anyway that's everything for today so if

you enjoyed it then do give us a like

and subscribe

and we'll see you next time