GCSE Physics - Specific Latent Heat #29
Summary
TLDRThis 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
🔥 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.
🌡️ 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.
Mindmap
Keywords
💡Specific Latent Heat
💡Kinetic Energy
💡Internal Energy
💡Temperature
💡Phase Change
💡Melting Point
💡Boiling Point
💡Specific Latent Heat of Fusion
💡Specific Latent Heat of Vaporization
💡Energy Calculation
💡Substance
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
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