Joy of Science Discovering the matters and the laws of the universe

Key Words Universe, Energy, Quantum mechanics, Chemical reaction, Structure of matter

Unless otherwise noted, copied pictures are taken from wikipedia.org

The first law of thermodynamics

n  The first law of thermodynamics: In an isolated system the total amount of energy, including heat, is conserved è The law of energy conservation è The kind of energy in a given system can change, but the total amount cannot!

The first law of thermodynamics:

Quiz 1 n  Eventually, all energy generated on the Earth is returned to

space as 1. heat 2. gravitational energy 3. work 4. potential energy

Quiz 1 n  Eventually, all energy generated on the Earth is returned to

space as 1. heat 2. gravitational energy 3. work 4. potential energy

Quiz 2

n  ( ) is the temperature at which all atomic and molecular kinetic motion ceases

1. The freezing point 2. The critical point 3. Absolute zero 4. 0 degrees Celsius

Quiz 2

n  ( ) is the temperature at which all atomic and molecular kinetic motion ceases

1. The freezing point 2. The critical point 3. Absolute zero 4. 0 degrees Celsius

Quiz 3

n  All isolated systems will spontaneously tend toward disorder. The phenomenon is referred to as

1. thermal inefficiency 2. heat transfer 3. entropy 4. thermal conductivity

Quiz 3

n  All isolated systems will spontaneously tend toward disorder. The phenomenon is referred to as

1. thermal inefficiency 2. heat transfer 3. entropy 4. thermal conductivity

Heat & Second law of thermodynamics Why is it easier to tear something down than to build it

Keyword Temperature; Absolute zero; Heat transfer: convection, conduction, radiation; Second law of thermodynamics, efficiency, entropy

November 7, 2016

Contents

n Introduction

n Three modes of heat transfer

n The second law of thermodynamics

1. Introduction - Nature’s direction - Terminology

Nature’s direction

n Throughout the universe, there are some natural tendency for things to become less orderly with time!

Nature’s direction

n Throughout the universe, there are some natural tendency for things to become less orderly with time!

Nature’s directionality

Nature’s direction: example

n The tendency of all systems to evolve from improbable to more probable states accounts for the directionality that we see in the universe around us!!!

Nature’s direction: example

n The tendency of all systems to evolve from improbable to more probable states accounts for the directionality that we see in the universe around us!!!

Ex1) Perfume scent disperses through a room when the perfume bottle is open

Nature’s direction: example

n Ex2) Billiard balls tend to be scattered than get together

Terminology: terms with heat

n Atoms never sit still, but move always while distributing their kinetic energy – so called, thermal energy or internal energy.

n  In order to understand the nature of heat and its movement, let us define three terms first:

- Heat, - Temperature, and - Specific heat capacity

Heat: A form of energy that moves from a warmer object to a cooler object à Heat is, therefore, energy in motion.

n Calories: a common unit of energy defined by “ the amount of heat required to raise 1 gram of room-temperature water by 1 degree Celsius in temperature” (In science, room temperature is usually taken to be either 20 or 25 degrees Celsius)

Temperature: A term that compares how vigorously atoms in a substance are moving and colliding in different substance

n Temperature:

Atoms have larger kinetic energy

Atoms have smaller kinetic energy

Solid(lower temperature) Liquid Gas(higher temperature)

Increasing Heat

Temperature: A term that compares how vigorously atoms in a substance are moving and colliding in different substance à The larger the temperature difference between two objects, the more rapidly heat is transferred.

n Temperature scales Every scale requires two easily reproduced temperatures for calibration – freezing and boiling points of pure water

n Temperature scales (cont’d) * Celsius scale : 0 and 100 degrees for freezing and boiling (degrees Celsius: most common) * Kelvin scale : same degrees as Celsius, with 100 increments between the freezing and boiling points of water (Kelvins: scientific) 0 oC = 273.15 K, 100 oC = 373.15 K -273.15 oC = 0 K *0 K: “absolute zero” – the temperature at which it is impossible to extract any heat

<Temperature conversions> It is often necessary to convert from one temperature scale to another *Fahrenheit scale : 32 and 212 degrees for freezing and boiling, respectively (degrees Fahrenheit) degrees F = ( 9/5 X degrees C ) + 32 degrees C = (degrees F – 32) X 5/9 Ex) 10 oC à 50 oF , 95 oF à 35 oC

n Specific heat capacity: A measure of the ability of a material to absorb heat, defined by “ The quantity of heat required to raise the temperature of 1 gram of that material by 1 degree Celsius”

n When we boil water in a copper pot, …

èWater absorbs 10 times more heat per gram than copper to raise its temperature

Specific heat capacity: example (cont’d)

n When we boil water in a copper pot, …

èWater absorbs 10 times more heat per gram than copper to raise its temperature à The ability of water to store thermal energy is bigger than that of copper.

Specific heat capacity: example (cont’d)

n When we boil water in a copper pot, …

èWater absorbs 10 times more heat per gram than copper to raise its temperature à The ability of water to store thermal energy is bigger than that of copper. In fact, Water has the largest heat capacity of any common substance.

Specific heat capacity: example (cont’d)

2. Three modes of heat transfer

Heat transfer

You can not prevent heat from moving from an object at high temperature to its cooler surroundings!

Heat transfer n Heat transfer: the process by which heat

moves from one place to another n There are three basic mechanisms of heat

transfer: Conduction, Convection, and Radiation

Conduction

atoms of metal

metal

Conduction

Heat

atoms of metal

metal

Conduction

n  If a piece of metal is heated at one end, the atoms and their electrons at that end begin to move faster

Heat

atoms of metal

metal

Conduction

n  If a piece of metal is heated at one end, the atoms and their electrons at that end begin to move faster

à They vibrate and collide with other atoms farther away from the heat source à A chain of collision occurs farther and farther èèEnergy is transferred to molecules farther away from the heat source

Conduction

n Conduction: An energy transfer mode between bodies of matter due to temperature difference through the action of individual atoms or molecules that are linked together by chemical bonds

Energy is transferred from one part to the other parts by vibrations and collisions of particles

HEAT

Conduction

n Thermal conductivity: The ability to transfer heat from one molecule to the next by conduction. Materials differ in their thermal conductivity. * Heat conductor: It moves heat rapidly Ex) metals – copper, silver, aluminum * Heat insulator: It resists the flow of heat transfer Ex) glass, paper, wood

Convection

n Convection: The transfer of heat by the bulk of fluid, such as air or water

n Convection cell: Each of regions of rising and sinking fluid

Convection n  Example: Boiling water in a pot on a stove has a rolling, churning motion as the water moves and mixes through convection, and the places where water bubbles up and where bubbles tend to collect are convection cells. è Heat is carried from the burner through the convection of the water and is eventually transferred to the atmosphere. è Convection is thus a very efficient way of transferring heat

Radiation n Radiation: The transfer of heat by electromagnetic radiation, a form of wave energy

Radiation: example

IH

Glowing red hot heat

Glowing red hot above a fireplace or an electric heater: infrared radiation è You perceive heat b/c of the energy that the infrared radiation carries to your hand

Radiation n All objects in the universe radiate energy in

this way: Under normal circumstances, as an object gives off radiation to its surroundings, it also receives radiation from those surroundings è No net loss of energy under a kind of equilibrium set up n Radiation is the only kind of energy that can

travel through the emptiness of space.

Radiation

n  Radiation is the only kind of energy that can travel through the emptiness of space.

Sun

Energy transfer by the form of radiation

n  In the real world, all three types of heat transfer occur all the time

Convection

Conduction Convection zone

Radiation

IH

3. The second law of thermodynamics

n The second law of thermodynamics states the

common sense of the direction of energy flow

3. The second law of thermodynamics

n  The second law of thermodynamics in different statements

1. Heat will not flow spontaneously from a cold to a hot body

3. The second law of thermodynamics

n  The second law of thermodynamics in different statements

1. Heat will not flow spontaneously from a cold to a hot body 2. You cannot construct an engine that does nothing but convert heat to useful work

3. The second law of thermodynamics

n  The second law of thermodynamics in different statements

1. Heat will not flow spontaneously from a cold to a hot body 2. You cannot construct an engine that does nothing but convert heat to useful work 3. Every isolated system becomes more disordered with time

3. The second law of thermodynamics

n  The second law of thermodynamics in different statements

1. Heat will not flow spontaneously from a cold to a hot body 2. You cannot construct an engine that does nothing but convert heat to useful work 3. Every isolated system becomes more disordered with time è These three statements appear differently, but they are actually logically equivalent!!

3. The second law of thermodynamics

n This statement describe the behavior of two objects at different temperatures:

From everyday observations, we find that in our universe heat flows in only one direction, from hot to cold

Statement1: Heat will not flow spontaneously from a cold to a hot body

n This statement describe the behavior of two objects at different temperatures:

From everyday observations, we find that in our universe heat flows in only one direction, from hot to cold èAt the molecular level: Faster-moving molecules tend to share their energy with slower-moving ones by collisions

Statement1: Heat will not flow spontaneously from a cold to a hot body

n This statement tells us that: If you wish to cool something down, this action cannot take place “spontaneously”

Statement1: Heat will not flow spontaneously from a cold to a hot body

n This statement tells us that: If you wish to cool something down, this action cannot take place “spontaneously” è you must supply energy

Statement1: Heat will not flow spontaneously from a cold to a hot body

n This statement tells us that: If you wish to cool something down, this action cannot take place “spontaneously” è you must supply energy è

A refrigerator will not work unless it is plugged in!

Statement1: Heat will not flow spontaneously from a cold to a hot body

n Energy can be defined as the ability to do work!

Statement2. You cannot construct an engine that does nothing but convert heat to useful work

n This second statement tells us: “ Whenever energy is transformed from heat to another type, some of that heat must be dumped into the environment and is unavailable to do work”

Statement2. You cannot construct an engine that does nothing but convert heat to useful work

n This second statement tells us: “ Whenever energy is transformed from heat to another type, some of that heat must be dumped into the environment and is unavailable to do work” è perpetual motion is impossible!

Statement2. You cannot construct an engine that does nothing but convert heat to useful work

Perpetual motion is impossible!

Heat

Engine

electricity, potential energy, …

Source Energy Environment

Work

Statement2. You cannot construct an engine that does nothing but convert heat to useful work

Heat

Engine

electricity, potential energy, …

Source Energy Environment Heat loss

Work

Statement2. You cannot construct an engine that does nothing but convert heat to useful work

Perpetual motion is impossible!

Heat

Engine

electricity, potential energy, …

Source Energy Environment Heat loss

Work

Statement2. You cannot construct an engine that does nothing but convert heat to useful work

Perpetual motion is impossible!

useless

n  For example, when fossil fuels are burned to produce a high-temperature reservoir and generate electricity, a large portion of energy must simply be thrown away

* High temperature reservoir: Exploding hot-gas mixture * Low temperature reservoir: Atmosphere into which the heat of compression is dumped

Engine

Electricity

Fossil fuels Heat loss

Work

Heat

Environment

Statement2. You cannot construct an engine that does nothing but convert heat to useful work

useless

High temperature reservoir

Low temperature reservoir

n Efficiency quantifies the loss of useful energy “ Efficiency is obtained by comparing the temperature difference between the high temperature and low temperature reservoirs with the temperature of the high temperature reservoir” efficiency= hot temperature – cold temperature hot temperature

X 100 (percent)

Statement2. You cannot construct an engine that does nothing but convert heat to useful work

Statement3. Every isolated system becomes more disordered with time

Statement3. Every isolated system becomes more disordered with time Statistics

Statement3. Every isolated system becomes more disordered with time

n  “order”: with pattern n  “disorder”: without pattern

Statement3. Every isolated system becomes more disordered with time

n  “order”: with pattern n  “disorder”: without pattern

Order

Disorder

Picture taken from www.jcit.com.cn/

Statement3. Every isolated system becomes more disordered with time

n The meaning of “order”: A number of objects – any small like atoms or big ones like automobiles - contained a system are positioned in a completely regular and predictable pattern

n The meaning of “disorder”: Objects in a system are randomly situated, without any obvious pattern

n This statement describes the tendency of systems all around us to become increasingly disordered

Statement3. Every isolated system becomes more disordered with time

n This statement describes the tendency of systems all around us to become increasingly disordered

Ex) A carefully cleaned room gets messy.

Statement3. Every isolated system becomes more disordered with time

n This statement describes the tendency of systems all around us to become increasingly disordered

Ex) A carefully cleaned room gets messy. A brand new car becomes dirty and scratched.

Statement3. Every isolated system becomes more disordered with time Statistics

n This statement describes the tendency of systems all around us to become increasingly disordered

Ex) A carefully cleaned room gets messy. A brand new car becomes dirty and scratched. All our bodies gradually get old and wear out.

Statement3. Every isolated system becomes more disordered with time

3. The second law of thermodynamics

Disorder has more probability of arrangement

Order Disorder

3. The second law of thermodynamics

Disorder has more probability of arrangement

Order: less probable Disorder: more probable

n Highly ordered configurations are less probable:

Almost possible configurations are disordered è Ordered: low probability Disordered: high probability

Statement3. Every isolated system becomes more disordered with time Statistics

n Define “a measure of disorder”: Entropy

Statement3. Every isolated system becomes more disordered with time

n Define “a measure of disorder”: Entropy Ordered = low or small entropy Disordered = high or large entropy

Statement3. Every isolated system becomes more disordered with time

“ The entropy of an isolated system remains constant or increases. ”

The second law of thermodynamics

The second law of thermodynamics

n Entropy: small entropy: low probability large entropy: high probability n  In probability theory, the entropy of any arrangement of atoms is related to the number of possible ways that you can achieve that arrangement

n Examples of increase of entropy: - Without careful driving, collections of automobiles tend to become more disordered - Without careful chemical and physical controls, atoms and molecules tend to become more intermixed

3. The second law of thermodynamics

n  “The entropy of an isolated system remains constant or increases.”

One part of a system can become more ordered, while another part of the system becomes more disordered. Ex) A freezer with a power code

3. The second law of thermodynamics

n Ex) A refrigerator with a power code

3. The second law of thermodynamics

Inside refrigerator

Warmer food à Cooler

Outside Cooler airà Warmer

Electricity supply

Behind fridge Heat rejected to air

Power code

n Ex) A refrigerator with a power code

3. The second law of thermodynamics

Inside refrigerator

Warmer food à Cooler More ordered

Outside Cooler air à Warmer More disordered

Electricity supply

Behind fridge Heat rejected to air

Power code

n Ex) A refrigerator with a power code 3. The second law of thermodynamics

Inside refrigerator Outside Cooler air à Warmer More disordered Entropy increases

Electricity supply

Behind fridge Heat rejected to air

Power code

Warmer food à Cooler More ordered Entropy decreases

n Ex) A refrigerator with a power code è The system’s total entropy must increase!

3. The second law of thermodynamics

Inside refrigerator

Warmer food à Cooler More ordered Entropy decreases

Outside Cooler air à Warmer More disordered Entropy increases

Electricity supply

Behind fridge Heat rejected to air

Power code

Next topic is, Electricity and Magnetism

: Chapter 3

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