Chapter 4: Heat Capacity and Heat Transfer - · PDF fileChapter 4: Heat Capacity and Heat...

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Chapter 4: Heat Capacity and Heat Transfer

Navapadol Kittiamornkul, Ph. D.

Chapter 4:

Heat Capacity and Heat Transfer

4.1 Material Structure4.2 Temperature and Material

Properties4.3 Heating and Internal Energy4.4 Heat Capacity and Latent Heat4.5 Heat Transfer

Chapter 4: Heat Capacity and Heat Transfer

4.1 Material Structure

Atom The smallest unit of element.

Molecule The smallest unit of compound consist of many atoms

Ex. Molecule of water (H2O) consists of 2 hydrogen atom and 1 oxygen atom

The Phase of Matter: Solid

Solid Molecules constructs together with strong bond.

Therefore, solid has definite volume and shape.

The Phase of Matter: Liquid

Liquid Molecules can freely move, but it cannot move so far because of its bond.

Therefore, liquid has a definite volume but no definite shape.

So, it can change its shape according to it container.

The Phase of Matter: Gas

Gas Molecules can freely move with long distance because it has weak bond.

Therefore, gas has neither a definite volume nor shape.

So, it can change its shape according to it container like liquid.

Moving Ability of Molecules

Solid < Liquid < Gas

Kinetic Energy of Molecules

Internal Energy of Molecules

4.2 Temperature and Material Properties

Temperature A measure of the warmth or coldness of an object which depends on internal energy (kinetic energy) of material.

High internal energy High temperature

Low internal energy Low temperature

Temperature Scale

Temperature scale in Kelvin, T(K) depends on internal energy (kinetic energy)

When T(K) is low, the molecules will move slowly until it stop at 0 K called “absolute zero”

Temperature measurement device called “Thermometer”

Advantage: Mercury thermometer can hold the value although it doesn’t contact patient. (User needs to flick before

measure)Mercury thermometer

Disadvantage: Mercury is toxic.

Digital thermometer

Now, mercury thermometer is replaced by Digital thermometer.

Material will extend when its temperature increase.

Material will shrink when its temperature decrease.

Because of kinetic energy, when kinetic energy of molecule increases, molecule velocity increase too. It causes the distance between molecules higher.

The relation between temperature change and material extending is linear

High temperatureLow temperature

Length difference

Referent length

Coefficient of linear expansion

Temperature difference

Example of coefficient of linear expansion

Ex. Lead has 3 cm of its length. If temperature increases from 37 ºC to 40 ºC, find the length after heating.

Mercury thermometer has bulbto contain liquid mercury at the terminal. Mercury will extend and flow to glass tube when temperature around its bulb increases.

To construct railway, we need to abstain around joint for extending of metal to protect the derailing.

4.3 Heating and Internal Energy

The energy occurs from the difference of temperature called “Heat”.

In natural, heat transfers from high temperature to low temperature till equilibrium called “Thermal Equilibrium”.

Material that receives heat will increase temperature.

Material that losses heat will decrease temperature.

Material temperature is not only changed by heating, but it is also changed by mechanical energy and etc.

James Joule’s experiment water insulator

thermometer

“Heat can change material phase.”

Exothermic

Endothermic

Exothermic

Endothermic

If we chill watermelon and sandwich, which one can hold longer temperature?

Two materials has the same mass (m), but difference heat capacity (s).

If we want to increase temperature, material that has more heat capacity (s) will need more energy (Q)

Heat Energy (Q)

If we give the same energy (Q) to two materials, material that has more heat capacity (s) will change its temperature slowly.

Ex. (A) Find heat energy that increases 200g water temperature for 5 degree Celsius. (Swater = 1 cal/g.C)

Ex. (B) Find heat energy that increases 200g lead temperature for 5 degree Celsius. (Slead = 0.03 cal/g.C)

Phase Change

Water + Ice

Give 1 cal/s of heat energy to 1 g of ice.

Water + Vapor

Water + Ice

Water + Vapor

Water + Ice

Water + Vapor

No temperature change

4.4 Heat Capacity and Latent Heat

Exothermic

EndothermicExothermic

Endothermic

liquid

condensation vaporization

fusionfreezing

Heat is used to change phase called Latent Heat.

Q v = Energy of vaporizationL v = Latent heat of vaporization

Q f = Energy of fusionL f = Latent heat of fusion

We can calculate energy that uses to change phase using the following equation.

Ex. Aluminum glass contains 800 g of water

4.5 Heat Transfer

Heat conduction

Heat Convection

Radiation

Conduction Heat transfer of material from contact

Convection Heat transfer of material using mass movement Ex. Water in boiler boils thoroughly.

Radiation Heat transfer of light, ray, electromagnetic wave, or etc. It can be exothermic and endothermic.

4.5 Heat Transfer

“Heat transfer occurs from collision of molecules at the contact point”

K.E. of foot molecule is higher than floor. K.E. will transfer to floor Temperature reduces

Feel Cool

4.5 Heat Transfer

“Heat transfer occurs from collision of molecules at the contact point”

K.E. of foot molecule is lower than floor. K.E. will transfer to foot Temperature increases

Feel Hot

4.5 Heat Transfer

Heat Convection

In natural, heat convection occurs when object receives heat.

Although gas and liquid are not good at heat conduction, it is good at heat convection. Molecules of gas and liquid can flow for long distance, and they will bring heat energy together.

It occurs together with movement of medium.

4.5 Heat Transfer

Radiation

Object releases electromagnetic energy called radiation

Electromagnetic wave can travel without medium. Ex. Light from the sun can travel passing space to the earth.

4.5 Heat Transfer

In still air, heat from flame transfers with radiation process.

In flow air, heat from flame transfers with convection process.

4.5 Heat Transfer

Heat and Human body

If human has high body temperature or low body temperature, it can cause very dangerous disease such as heat stroke and hypothermia.

How to make body temperature lower.

END OF CHAPTER 2

END OF CHAPTER 4

Heat Capacity and Heat Transfer

Chapter 4: Heat Capacity and Heat Transfer - · PDF fileChapter 4: Heat Capacity and Heat...

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