Heating Curve Grade 10: Kinetic Molecular Theory

Summary

In this educational video, Miss Martins explores the kinetic molecular theory's application to heating curves, emphasizing the distinction between heat energy and temperature. She explains that adding heat doesn't always raise a substance's temperature, highlighting phase changes where heat energy is used to overcome intermolecular forces without increasing temperature. The video uses the heating curve of water as an example, illustrating how temperature remains constant during melting and boiling, and encourages viewers to understand the kinetic theory's implications for phase changes.

Takeaways

• 🔥 The kinetic molecular theory explains the behavior of particles in a substance when heat is applied.
• ⏱️ A heating curve is a graphical representation of the temperature change of a substance over time during heating.
• ⚠️ Adding heat to a substance does not always result in a temperature increase; the energy can be used for phase changes.
• 📊 The flat parts of a heating curve indicate a phase change is occurring, where energy is used to overcome intermolecular forces without increasing temperature.
• 💧 The heating curve of water shows distinct phases: solid (ice), liquid, and gas, with phase changes at specific temperatures.
• 🌡️ The melting point and boiling point of a substance are represented by the horizontal sections of the heating curve, where temperature remains constant during phase change.
• 📉 On the heating curve, the inclined parts represent periods where the substance is in a single phase and its temperature is increasing due to added heat.
• 🔍 The axes of a heating curve are crucial, with the y-axis representing temperature in degrees Celsius and the x-axis representing time in minutes.
• 🌟 The kinetic molecular theory states that when a substance is heated, it can either increase in temperature (if in the same phase) or undergo a phase change without a temperature increase.
• 🔄 During phase changes, such as melting (solid to liquid) or boiling/evaporation (liquid to gas), both phases coexist, and the added heat energy is used to weaken intermolecular forces.

Q & A

What is the kinetic molecular theory?

The kinetic molecular theory is a concept that explains the behavior of particles in a substance when energy is added or removed. It relates to how substances change phases and how their temperature changes with the addition of heat energy.

What is a heating curve and how is it represented?

A heating curve is a graphical representation that shows the change in temperature of a substance over time as heat is added. It typically has time on the x-axis and temperature on the y-axis.

Why doesn't the temperature of a substance always increase when heat is added?

The temperature of a substance doesn't always increase when heat is added because the energy can be used for phase changes, such as melting or boiling, where the intermolecular forces are overcome without increasing the temperature.

What is the significance of the flat parts of a heating curve?

The flat parts of a heating curve indicate that a phase change is occurring. During these periods, the substance absorbs heat energy to change its state without a rise in temperature.

What are the two possible outcomes when heat is added to a substance according to the kinetic molecular theory?

When heat is added to a substance, the kinetic molecular theory suggests two possible outcomes: an increase in temperature due to increased average kinetic energy, or no increase in temperature as the energy is used to overcome intermolecular forces during a phase change.

Why is it important to label the axes of a heating curve correctly?

Labeling the axes of a heating curve correctly is important for clarity and accuracy. It ensures that the graph is easily understood, with the y-axis typically representing temperature and the x-axis representing time.

What is the difference between the inclined and horizontal parts of a heating curve?

The inclined parts of a heating curve represent periods where the substance is in a single phase and its temperature is increasing due to added heat. The horizontal parts indicate phase changes, where the substance is transitioning from one state to another without a change in temperature.

What is the melting point and boiling point of water, and how do they relate to the heating curve?

The melting point of water is around 0 degrees Celsius, and the boiling point is around 100 degrees Celsius. These points are significant on the heating curve as they mark the transition from solid to liquid (melting point) and liquid to gas (boiling point).

How can you identify the phase or phases present during different parts of a heating curve?

You can identify the phase or phases present during different parts of a heating curve by observing the inclined and horizontal sections. Inclined sections indicate a single phase, while horizontal sections indicate a phase change where two phases coexist.

What is the role of intermolecular forces in the context of a heating curve?

Intermolecular forces play a crucial role in a heating curve as they resist changes in the state of a substance. During phase changes, the added heat energy is used to weaken these forces, allowing the substance to transition from one phase to another without an immediate increase in temperature.

Outlines

00:00

🔍 Introduction to Kinetic Molecular Theory and Heating Curves

This paragraph introduces the concept of the kinetic molecular theory and its relation to heating curves. The narrator, Miss Martins, explains that a heating curve is a graphical representation of the temperature change of a substance over time when heat is applied. She emphasizes that adding heat to a substance does not always result in a temperature increase, highlighting the distinction between heat energy and temperature. The paragraph sets the stage for a deeper exploration of how heating curves can be used to understand phase changes in substances like water, with specific reference to melting and boiling points.

05:02

🌡 Understanding Heating Curves and Phase Changes

In this paragraph, the focus is on the mechanics of heating curves and how they illustrate phase changes. The narrator uses the example of water to explain that during phase changes, such as melting and boiling, the temperature remains constant despite continuous heat input. This is because the added heat energy is used to overcome intermolecular forces, facilitating the transition from one phase to another without a change in temperature. The inclined parts of the heating curve represent periods where the substance's temperature increases due to absorbed heat, while the horizontal parts indicate phase changes where the energy is used to change the state of the substance rather than increase its temperature.

10:04

📊 Analyzing Phases and Phase Changes in Heating Curves

The final paragraph delves into the specifics of identifying phases and phase changes from a heating curve. The narrator clarifies that during the flat parts of the curve, two phases coexist as the substance undergoes a phase change. For example, during melting (solid to liquid) and boiling/evaporation (liquid to gas), both the initial and final phases are present. The narrator also invites viewers to request past paper questions for practice and encourages engagement through comments. The summary ends with a call to action for viewers to subscribe, share, and like the video, and expresses well wishes for their studies.

Keywords

💡Kinetic Molecular Theory

The Kinetic Molecular Theory is a model that explains the behavior of gases by considering the gas as composed of a large number of small particles in constant, random motion. In the context of the video, this theory is used to explain how heating a substance affects its temperature and phase. The video emphasizes that when heat is added to a substance, it does not always result in an increase in temperature due to the energy being used for phase changes rather than increasing the kinetic energy of the particles.

💡Heating Curve

A heating curve is a graphical representation that shows the change in temperature of a substance over time as it is heated. The video uses the heating curve to illustrate how the temperature of a substance can remain constant during phase changes, such as melting and boiling, despite continuous heat input. The curve helps to visualize the kinetic molecular theory in action, showing the relationship between temperature, time, and the phase of the substance.

💡Phase Change

A phase change refers to the transformation of a substance from one state of matter to another, such as from solid to liquid (melting) or liquid to gas (boiling). The video script explains that during phase changes, the temperature of the substance does not increase even though heat is being added because the energy is used to break the intermolecular forces, causing the particles to move apart and change phase.

💡Temperature

Temperature is a measure of the average kinetic energy of the particles in a substance. The video clarifies that while adding heat increases the internal energy of a substance, it does not necessarily raise its temperature if the energy is used for a phase change. The script uses the example of water's heating curve to show how temperature remains constant during melting and boiling phases.

💡Heat Energy

Heat energy is the energy transferred between systems or particles due to a temperature difference. In the video, it is explained that when heat energy is added to a substance, it can either increase the substance's temperature (if no phase change is occurring) or be used to facilitate a phase change, during which the temperature remains constant.

💡Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion which act between molecules. The video script discusses how adding heat energy can weaken these forces, allowing particles to move further apart and thus facilitating a phase change. This concept is crucial for understanding why the temperature does not rise during melting or boiling.

💡Melting Point

The melting point is the temperature at which a solid changes into a liquid. In the video, the melting point is identified as the temperature where the heating curve becomes horizontal, indicating that the substance is undergoing a phase change from solid to liquid. The script uses the example of water's melting point being around zero degrees Celsius.

💡Boiling Point

The boiling point is the temperature at which a liquid changes into a gas. The video script explains that the boiling point is represented on the heating curve as the second horizontal section, where the substance transitions from liquid to gas. For water, this point is approximately 100 degrees Celsius.

💡Average Kinetic Energy

Average kinetic energy is the mean of the kinetic energies of all the particles in a substance. The video script mentions that when heat is added and the substance's temperature increases without a phase change, it is due to an increase in the average kinetic energy of the particles.

💡Phases of Matter

The phases of matter refer to the states in which matter can exist, such as solid, liquid, and gas. The video uses the heating curve to illustrate the different phases a substance can be in at various points during heating. The script explains that the substance can be in one phase or a combination of phases, particularly during phase changes.

Highlights

Kinetic molecular theory relates to the heating curve, showing the change in temperature of a substance over time.

Heating a substance involves adding energy, but it doesn't necessarily mean the temperature will increase.

The heating curve's flat parts indicate a phase change, where temperature remains constant despite added heat.

The x-axis typically measures time, while the y-axis measures temperature in degrees Celsius.

The heating curve of water is specifically labeled, showing phases and phase changes.

The boiling point of water is 100 degrees Celsius, indicated by the second horizontal part of the curve.

A proper graph should start at the origin, representing zero temperature and time.

The inclined parts of the curve represent when the substance is in one phase, with increasing temperature.

During phase changes, heat energy is used to weaken intermolecular forces, causing a phase change without a temperature increase.

The kinetic molecular theory explains that heating can either increase temperature or cause a phase change.

The horizontal parts of the graph indicate a phase change, where both phases are present.

The inclined parts of the graph show an increase in temperature without a phase change.

The video provides a detailed explanation of how to interpret the heating curve for substance X.

The video emphasizes the importance of understanding the difference between heat energy and temperature.

The video concludes with a call to action for viewers to engage with the content and seek further assistance if needed.

Transcripts

hello everybody and welcome back to

another video with me Miss Martins today

we're going to carry on with the kinetic

molecular theory and in particular we're

going to look at the kinetic molecular

theory and how it relates to the heating

curve now if you haven't watched part

one of the series I suggest you do that

now

as you can see a heating curve is

basically described as a curve that

shows the change in temperature of a

substance during a time period when

heating occurs now the first thing that

I want you to guys to understand is that

when we heat a substance we are adding

energy to the substance we are adding

heat energy to the substance and the

first thing that I want you to get

familiar with right off the bat is the

fact that if I add heat okay I'm adding

heat to the substance that does not

necessarily mean the temperature of the

substance increases so I want you to

understand that there is a difference

between heat

basically in other words for heat in

this context will be energy heat energy

and temperature so if you can see the

curve over here we'll discuss the axes

the hitting and everything

um in a second but you can basically see

that this is a measure of temperature as

time goes on and what's important to

understand is that sometimes the isn't

increasing you can see the flat parts of

the graph like over here this part over

here temperature is not increasing and

this part over here temperature is not

increasing so But as time is going on

I'm adding heat to the substance so

another measure another thing that can

be measured on this axis is actually

time and we are most commonly going to

see time in seconds or time in minutes

being measured on the x-axis and on the

y-axis temperature so let's look more

closely at the heating curve and how it

works as you can see here my heading is

heating curve of water this is showing

water in particular the substance water

another heading for this curve could be

temperature of water versus time in

minutes

as you can see on the y-axis which is

this one we've got temperature measured

in degrees celsius it's very important

when drawing a graph to look and label

your axes correctly with unit so

temperature degree celsius time in

minutes and we've got the curve over

here

now I've labeled this curve I've shown

in yellow this the phases present so

here you can see solid

then we've got solid and liquid then

we've got liquid then we've got liquid

and gas and then we've got gas see my

key OBS is phases in yellow and phase

change in green so you can see the first

horizontal of the graph represents

melting the second represents boiling or

evaporation remember both terms are

applicable and then I've also indicated

the boiling point over here which we

know for water is 100 degrees Celsius we

read it off over here the boiling point

is that where the graph reaches its

second flat it's second horizontal and

this over here

will be the melting point right now what

I want to point out with this graph is

that we've got our y-axis and our x-axis

over here and generally where y-axis and

our x-axis meet if you think of a

Cartesian plane that is the origin which

is a zero zero position over here

they've kind of drawn very strangely and

they started with negative 40. that's

not really how we like to do it so we

like to draw our graphs looking more

like this

as you can see this is the y-axis

this is the x-axis

temperature versus time and we can see

here where those two axes cross that is

the origin it's the zero position if I

temperatures below zero we generally

draw it below the x-axis like this so

for example this would be negative 100

or negative 10 or negative 50 or

whatever

this would be a better representation of

a consent curve so let's take a look at

this one and discuss it in more detail

so it says the heating curve of now in

this case I said water this will not be

the heating curve of water and I wonder

if you guys can tell me why think about

it for a second so this I'm going to

change it to substance X

this would not represent the heating

curve of water let's say heating curve

of substance X or remember another way

that I can label this graph another

heading that I could use is temperature

versus time for heating of substance X

the reason why this graph would not

represent water or the heating curve of

water is because look at the melting

point so the first horizontal of the

graph is the melting point

and look at the boiling point the second

horizontal of the graph the melting

points at negative 20. the boiling point

is at 80 and we can read it off there we

know that the melting point of water is

around zero degrees Celsius not negative

20 and the boiling point is around 100

degrees Celsius not 80. so that's why I

change it to substance X but the most

important thing that I want you to

notice is my Axis so temperature versus

time as time goes on we are adding heat

energy

but let's discuss what happens in this

graph so we start off with solid phase

so I'm going to use my yellow again like

I did in the previous example to

indicate my phases so that is solid

this over here so I'm going to use this

this is solid phase

okay this over here is when my object or

when my substance is in its liquid phase

and this over here is when my substance

is in its gas phase we know that as I

add heat to substitutes it goes from

solid to liquid and liquid to gas okay

so the inclined Parts represent when my

substance is in one phase

then we've got the horizontal parts of

the graph now I need you to understand

what is actually happening in the

horizontal parts

now in the horizontal part so when I

mean horizontal I mean this product here

and this part over here

the horizontal part of the graph a phase

change is happening this is a phase

change

and what I mean by phase change is for

example we're going from a solid

to a liquid and that base change that

process is called melting

so the phase change that is happening is

solid to liquid the process is called

melting and over here we're going from a

liquid to a gas so this is another phase

change called boiling or evaporation

now why is the graph horizontal here

well what you need to notice is that

during phase changes so when a substance

is going from one phase to another solid

to liquid liquid to gas during a phase

change

there is no increase in temperature and

you might be thinking but mum housing no

increase in temperature we are adding

heat we're adding heat so what's

happening why is there no increase in

temperature well basically what happens

is as I add heat to the substance

that heats energy

is not causing the temperature to

increase we can see the temperatures

constantly at negative 20. so it's not

causing the temperature to increase but

what it is doing is it is causing the

forces between the particles they are

called

intermolecular forces

it is causing the intermolecular forces

to weaken okay it we are overcoming

those intermolecular forces

basically breaking those forces up

breaking is not a great word to use

because we don't really break a force

we've we weaken the force uh we weaken

the forces and that is causing a phase

change so think about it in order to

weaken the forces in order to cause

those particles to move further and

further apart we need energy

so all that energy that we're adding is

going into the phase change process it's

going into weakening those

intermolecular forces that's why there's

not enough energy to increase the

temperature I hope that makes sense

summarized it in the following way for

you

when we heat a substance according to

the kinetic molecular theory the kinetic

molecular theory one of two things can

happen now the first thing that can

happen is when we heat a substance so

basically we're adding heat we're adding

energy the first thing that can happen

is the temperature of the substance can

increase because of the heat absorbed

phase doesn't change in these instances

sausage are the average kinetic energy

of the particles and therefore the

temperature of the substance increases

remember average kinetic energy is a

measure of temperature I'm going to say

that again average kinetic energy is a

measure of temperature so if the average

kinetic energy increases as the

temperature increases but the substance

is still in the same phase so let us use

a color to illustrate that let's choose

yellow so the first thing that can

happen the temperature of the substance

can increase and I said yeah the

inclined parts of the graph so if we

look at another graph over here we can

see that that is this part so see

still in one face so it's still a solid

it's still a liquid yeah it's Stellar

gas there's no phase change but the

temperature is increasing

energies increasing

then the second

is I can add heat energy but the

temperature does not increase and then

you might think what happens to the heat

energy remember that heat energy is

being used to overcome the

intermolecular forces

it causes the particles to move further

and further apart that increases the

potential energy not kinetic energy so

you see I say temperature and kinetic

energy stays the same so it's the flat

parts of the graph

and during these stages so the flat

parts of the graph the temperature is

not increasing the kinetic energy is not

increasing all that energy is being used

to change phase so it's a phase change

happening

so another summary on the incline parts

of the graph that's what happens versus

on the flat parts of the graph that is

what happens and just take note that on

the flat parts of the graph when a phase

change is occurring we actually have two

phases present so this is malting this

is the the process melting is happening

over here a solid is being changed into

a liquid that's the phase change both

solid and liquid are present over here

the flat part we've got a phase change

so we're going from liquid to gas it's

called boiling or evaporation boiling

and both liquid and gas are presents

over there

so your new

be able to identify the phase or phases

present so a b will

be well BC will be a solid and a liquid

CD

remember it's an X inclined part will be

a liquid

d e will be a liquid and a gas that's

where the phase change is happening

remember both phases are presence and EF

will be a gas

and if they ask you for face changes

just remember that BC will be melting so

that's solid to liquid d e will be

boiling evaporation so that's liquid to

gas

if you want to see past paper questions

like this one please let me know in the

comments below let me know what else you

need help with and I wish you the very

best for all your preparations and all

your studies Please Subscribe share this

video give it a thumbs up if you haven't

yet

um and I hope to see you guys soon