Physics 22 Introduction to Heat & Temperature (6 of 6) Change of Phase & Latent Heat

Summary

This script delves into the concept of phase changes in thermodynamics, focusing on the latent heat associated with these transitions. It illustrates the process using the example of water, explaining how much heat is required to melt one gram of ice or to evaporate one gram of boiling water. The script clarifies the difference between latent heat of fusion (80 calories per gram for ice to water) and latent heat of vaporization (540 calories per gram for water to vapor), emphasizing the significant energy involved in phase changes without a change in temperature.

Takeaways

• 🔍 The topic of discussion is the change of phase in materials and associated latent heat in thermodynamics.
• 🧊 Discussing the example of adding one calorie of heat to one gram of water, which is expected to increase the temperature by one degree Celsius.
• ❄️ When one gram of ice at zero degrees Celsius is heated, it begins to melt, and a significant amount of heat is required to completely melt it.
• 🔥 The transition from solid to liquid or liquid to gas requires energy, which is referred to as latent heat.
• 🔑 The phase change from solid to liquid requires breaking the bonds that lock atoms in position, allowing molecules to vibrate and eventually roll over each other.
• 🌡️ It takes 80 calories to completely melt one gram of ice at zero degrees Celsius, which is 80 times more than raising the temperature of water by one degree Celsius.
• 💧 To evaporate one gram of boiling water at 100 degrees Celsius, 540 calories are required, indicating the large amount of energy needed for phase change.
• ⚖️ The equation for phase change heat is Q = M * L, where Q is the heat added, M is the mass, and L is the latent heat of the material.
• 🔄 The latent heat of fusion is the energy required to change from solid to liquid, and the latent heat of vaporization is for changing from liquid to gas.
• 📏 The units for latent heat are energy per gram or energy per mass, with the grams canceling out, leaving calories as the unit.
• 🌟 The concepts of latent heat of fusion and latent heat of vaporization are applicable to all substances, not just water.

Q & A

What is the main topic discussed in the script?

The main topic discussed in the script is the change of phase of materials and the associated latent heat in thermodynamics.

What happens when you add one calorie of heat to one gram of water in an isolated container?

When you add one calorie of heat to one gram of water in an isolated container, you expect a temperature increase of one centigrade degree.

How does the process of melting ice differ from raising the temperature of water?

Melting ice requires adding heat without a change in temperature until the phase change is complete, whereas raising the temperature of water involves a continuous increase in temperature with added heat.

What is the amount of heat required to completely melt one gram of ice at zero degrees centigrade?

The amount of heat required to completely melt one gram of ice at zero degrees centigrade is approximately 80 calories.

What is the term used for the energy required to change the phase of a substance?

The term used for the energy required to change the phase of a substance is latent heat.

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

The two types of latent heat mentioned in the script are latent heat of fusion (change from solid to liquid) and latent heat of vaporization (change from liquid to gas).

How much heat is required to completely evaporate one gram of boiling water at 100 degrees centigrade?

It takes 540 calories to completely evaporate one gram of boiling water at 100 degrees centigrade.

Why is the energy required to change the phase of water from solid to liquid or liquid to gas so high?

The energy required is high because the molecules need to overcome the intermolecular forces and gain enough energy to change their state, which is significantly more than what is needed to raise the temperature by one degree centigrade.

What is the formula used to calculate the amount of heat required for a phase change?

The formula used to calculate the amount of heat required for a phase change is Q = M * L, where Q is the heat energy, M is the mass of the substance, and L is the latent heat of the material.

How does the temperature change during the phase change process?

During the phase change process, the temperature remains constant until the phase change is complete, even though heat is being added or removed.

What is the significance of latent heat in understanding phase changes?

The significance of latent heat in understanding phase changes is that it quantifies the amount of energy required to change the state of a substance without changing its temperature, which is crucial in processes like melting and evaporation.

Outlines

00:00

🌡️ Phase Change and Latent Heat in Thermodynamics

This paragraph introduces the concept of phase change in thermodynamics, focusing on the transformation of materials from solid to liquid and from liquid to gas. It uses the example of one gram of water to illustrate the process. The discussion highlights the significant amount of energy, or latent heat, required for these changes. Specifically, it mentions that 80 calories are needed to melt one gram of ice at zero degrees Celsius, and 540 calories are required to evaporate one gram of boiling water at 100 degrees Celsius. The concept of latent heat is explained, distinguishing between latent heat of fusion (solid to liquid) and latent heat of vaporization (liquid to gas). The importance of understanding these energy requirements is emphasized, as they are fundamental to the study of thermodynamics.

05:01

🔥 Understanding Latent Heat of Fusion and Vaporization

In this paragraph, the focus is on the mathematical representation of the latent heat involved in phase changes. It explains that the heat required for a phase change, denoted as Q, can be calculated using the formula Q = M * L, where M is the mass of the substance undergoing the phase change and L is the latent heat. The paragraph clarifies that the latent heat of fusion is the energy needed to change a solid to a liquid, and the latent heat of vaporization is the energy needed to change a liquid to a gas. The units of latent heat are energy per gram, and the example of water is used to demonstrate that 80 calories per gram are required for fusion and 540 calories per gram for vaporization. The summary underscores the importance of recognizing the energy differences between temperature changes and phase changes in thermodynamics.

Keywords

💡Thermodynamics

Thermodynamics is the study of the movement of heat and its conversion to and from other forms of energy. In the video, it is the overarching theme as it discusses the phase changes of materials and the associated latent heat, which are fundamental concepts in understanding energy transfer and state changes.

💡Phase Change

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 uses the example of water changing from ice to liquid and then to vapor to illustrate the concept of phase change and the energy required for these transitions.

💡Latent Heat

Latent heat is the amount of heat absorbed or released by a substance during a phase change at a constant temperature. The script explains that latent heat is significant when comparing the energy needed to change the state of a substance versus raising its temperature, as seen with the melting of ice and the evaporation of water.

💡Calorie

A calorie is a unit of energy, often used to express the energy content of food or the energy required for physical or chemical changes. In the context of the video, calories are used to quantify the amount of heat needed to melt ice or evaporate water, emphasizing the large energy differences between temperature change and phase change.

💡Isolated System

An isolated system is one that does not exchange matter or energy with its surroundings. The script mentions an isolated container to illustrate how adding heat to water or ice in such a system would result in phase changes without a change in temperature, highlighting the concept of latent heat.

💡Molecules and Atoms

Molecules and atoms are the basic units of matter. The script describes how, during phase changes, the bonds between atoms in a solid are overcome by heat, allowing molecules to move more freely as in a liquid, or to separate entirely and become a gas.

💡Vibration

Vibration refers to the oscillatory motion of particles. In the script, the increased vibration of water molecules due to heat is described as the process that leads to the breaking of intermolecular bonds and the transition from solid to liquid, and then liquid to gas.

💡Melting

Melting is the process by which a solid substance absorbs heat and becomes a liquid. The video uses the example of ice at zero degrees Celsius to explain the amount of heat (80 calories) required to completely melt one gram of ice, illustrating the concept of latent heat of fusion.

💡Evaporation

Evaporation is the process by which a liquid turns into a vapor at its surface. The script discusses the large amount of heat (540 calories) needed to evaporate one gram of boiling water, demonstrating the concept of latent heat of vaporization.

💡Latent Heat of Fusion

Latent heat of fusion is the amount of heat required to change a substance from a solid to a liquid without changing its temperature. The script provides the value for water as 80 calories per gram, showing the significant energy involved in the phase change from ice to water.

💡Latent Heat of Vaporization

Latent heat of vaporization is the amount of heat needed to change a substance from a liquid to a gas at a constant temperature. The video script emphasizes that it takes 540 calories to vaporize one gram of water at its boiling point, indicating the substantial energy required for this phase transition.

Highlights

Introduction to the topic of phase change in thermodynamics and associated latent heat.

Explanation of how adding one calorie of heat to one gram of water in an isolated container would typically increase its temperature by one degree Celsius.

Discussion on the melting of one gram of ice at zero degrees Celsius and the amount of heat required for complete melting.

The concept that phase change from solid to liquid or liquid to gas requires energy, specifically latent heat.

Description of the process of atoms breaking free from each other when enough heat is added to change a solid into a liquid.

The energy required to turn water into vapor, highlighting the large amount of heat necessary compared to raising temperature.

Quantitative comparison of energy needed to raise water temperature by one degree Celsius versus melting one gram of ice.

The specific amount of heat, 80 calories, required to completely melt one gram of ice at zero degrees Celsius.

The even greater amount of heat, 540 calories, required to completely evaporate one gram of boiling water.

Explanation of latent heat and its role in phase changes without a change in temperature.

The formula Q = M * L for calculating the amount of heat required for phase change, where M is mass and L is latent heat.

Differentiation between latent heat of fusion (solid to liquid) and latent heat of vaporization (liquid to gas).

The practical example of water's phase changes and the associated latent heats of fusion and vaporization.

The units of latent heat, energy per gram or energy per mass, and their significance in calculations.

The specific latent heat values for water: 80 calories per gram for fusion and 540 calories per gram for vaporization.

The importance of understanding phase change and associated latent heat in thermodynamics for practical applications.

Transcripts

welcome to electron line and the next

topic we're going to talk about in

thermodynamics is the change of phase of

materials and the Associated latent heat

as we call it so we go back to something

we're familiar with let's say we have a

little container and of course has to be

tiny little container because we're

talking about it containing one gram of

water and one gram of water is very very

tiny but let's say we add one calorie of

heat to that container and let's say the

container doesn't change temperature

it's isolated from the water to some

insulator and we add one calorie to the

water we expect a temperature increase

to be one centigrade degree now what

would happen if you took one gram of ice

at zero degree centigrade so the ice if

you now add any heat to the ice the ice

will begin to melt and the question then

would be how much heat do we add to one

gram of ice to completely melt that one

gram of ice and secondly let's say we

have a small container that has boiling

water in it at 100 degrees centigrade

and how much heat do we have to add to

the water to completely evaporate that

water so when we go from the solid state

to a liquid state or from a liquid state

to a gas state we go to what we call a

change of phase and in order to do that

it requires energy well first of all to

go from a solid state to liquid state

you have to go from a state where the

atoms are locked in position due to the

electrical bonds and then we add enough

heat the the molecules begin to vibrate

so finally that they actually break

loose from each other and they begin to

roll over each other like marbles would

roll over each other and so then you

turn a solid into a liquid then if you

continue add more and more heat the

vibrations continue to the point where

they get so much energy that they will

actually jump free from the water and

turn into a gas or in the case of water

it turns into a vapor and again that

requires a certain amount of energy and

you'd be surprised how much energy that

takes because it only takes one calorie

to take one gram of water and increase

of a one centigrade degree but to take

one gram of ice at zero degree

centigrade and you want to completely

melt it the heat required q is equal to

80 calories technically speaking it's

actually seventy nine point seven

calories

but we typically just call it 80

calories compared to how much it takes

to raise the temperature by one degree

centigrade it takes 80 times as much to

completely melt one gram of ice at zero

degree centigrade to liquid at zero

degree centigrade in an enormous amount

of heat not only that when you take

boiling water and you want to completely

evaporate it it takes even more heat the

cure required to completely evaporate

one gram of boiling water is equal to

540 calories without the words 540 times

as much as the energy required to take

one gram of water and raise this

temperature by one centigrade degree so

there you get kind of a feel of how much

heat it requires now it turns out since

the temperature doesn't change through

the phase in other words when one gram

of ice which start at 0 degree

centigrade completely melts that water

does not melt the water will still be at

0 degree centigrade so it still will be

at the same temperature there's no

temperature change so the equation we

use for that is Q is equal to M times L

M is the mass of the substance that

we're changing to a face and L is what

we call the latent heat of the of the

material so in the case of water so the

amount of heat required is equal to the

mass 1 gram times the latent heat of

fusion as we call it so let's call this

latent heat of fusion

I said well wait a minute fusing means

you take a liquid put into a solid

that's correct but it's the same energy

required to go both ways

so if you take one gram of water and

completely freeze it to a block of ice

of one gram at 0 degree centigrade then

of course you would have to take away

from that 80 calories of heat and

likewise they have 1 gram of steam at

100 degrees centigrade and allow it to

to liquefy to condense as we call it

then of course you have to remove 540

calories of heat in order for it to go

from a gas phase to a liquid phase so

this is called latent heat of fusion so

to indicate going from a liquid to a

solid and this is called latent heat of

vaporization which means going from a

liquid state to a gas phase so the term

ecology is from a liquid to frozen or

liquid to a gas phase so it's called

latent heat of vaporization of course

water is kind of a common substance and

we commonly go from liquid to solid salt

back to liquid and all for liquid eyes

and eyes back to liquid same with the

vaporization of course latent heat of

fusion and later heat of vaporization is

something you will see in all substances

of course we can talk about that later

but any weight so this would be equal to

80 calories per gram so notice that the

units are energy per gram or energy per

mass the grams cancel out of course

you're left with calories and here for

here for this change in face you say Q

is equal to M times L in this case the L

is the latent heat of vaporization and

so that would be equal to one gram times

540 calories per gram again notice that

the grams cancel out you're left with

calories and so this would of course be

540 calories required to change one gram

of boiling water to two of gas phase and

here Q would be equal to 80 calories

that's the heat required to take one

gram of ice at zero degree centigrade

and turn it completely into a liquid so

hopefully this will give you a good

understanding of what what the phase of

change the change of phases and what two

associated heat required is which is

called the latent heat of fusion or of

vaporization