Evaporation and condensation

Slides:



Advertisements
Similar presentations
Air Conditioners.
Advertisements

Chapter 15 Thermodynamics.
Air Conditioners. Introductory Question If you operate a window air conditioner on a table in the middle of a room, the average temperature in the room.
Lecture Outlines Chapter 17 Physics, 3rd Edition James S. Walker
The Laws of Thermodynamics
Chapter 9 Thermal Energy
Thermal Physics.
Chapter 22 Heat Transfer.
THERMAL ENERGY Integrated Science I Thermal Energy is heat energy; it is the total kinetic and potential energy of the particles making up the material.
L 19 - Thermodynamics [4] Change of phase ice  water  steam
Energy in Thermal Processes
Chapter Thermodynamics
© 2007 Pearson Prentice Hall This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their.
Copyright © 2010 Pearson Education, Inc. Lecture Outline Chapter 16 Physics, 4 th Edition James S. Walker.
1 L 19 - Thermodynamics [4] Change of phase ice  water  steam The Laws of Thermodynamics –The 1 st Law –The 2 nd Law –Applications Heat engines Refrigerators.
Chapter 13 Section 1 Temperature Objectives
Energy and Heat Transfer. Objectives Comprehend Forms of energy Energy conversion Heat transfer processes Principles of operation of various heat exchangers.
Lecture Outline Chapter 18 Physics, 4th Edition James S. Walker
PowerPoint Lectures to accompany Physical Science, 7e Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter.
The Laws of Thermodynamics
Changes of Phase List the four phases of matter in order of increasing internal energy.
Heat and temperature. Kinetic molecular theory Collective hypotheses about the particulate nature of matter and the surrounding space Greeks - earliest.
Thermodynamics. Heat Vs Temperature 4 Temperature is NOT heat! 4 Heat is energy (kinetic energy of atoms and molecules) 4 Temperature is the level of.
PowerPoint Lectures to accompany Physical Science, 9e
Chapter 6.  Temperature ◦ Is something hot or cold? ◦ Relative measure.
The Laws of Thermodynamics
Transmission of Heat. Conduction n Heat transfer due to direct contact n Either between different materials in thermal contact or different parts of the.
Chapter 4 Heat and Temperature An introduction to Thermodynamics.
Chapter 6: Thermal Energy
Section 1 Temperature and Heat. Kinetic Theory  All objects (even people) are made of particles and atoms that constantly and randomly move. All atoms.
Lecture Outline Chapter 12 College Physics, 7 th Edition Wilson / Buffa / Lou © 2010 Pearson Education, Inc.
Heat – Thermal Energy ISCI What is Heat? Place your finger on the handle of a ‘hot’ pan. Ouch! Heat is energy that is transferred from one ‘system’
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat and Temperature Chapter 13 Table of Contents Section 1 Temperature.
Heat Transfer  How does the energy move from a hotter to a colder object?  Three mechanisms  Conduction  Convection  Radiation.
A lesson in heat (and the study of it) Chapter 12
Chapter 6. Temperature related to the average kinetic energy of an object’s atoms or molecules Thermal energy the sum of kinetic & potential energy of.
CHAPTER 15 Thermodynamics Thermodynamic Systems and Their Surroundings Thermodynamics is the branch of physics that is built upon the fundamental.
Chapter 12: Thermal Energy What’s hot and what’s not…
Changes in State Chapter 2 Section 2. Energy How does the ice go from being a solid back to being a liquid? Energy is the ability to do work Energy.
Chapter 5 Thermal Energy
Conduction, Convection, and Radiation
Conduction, Convection and Radiation. Radiation: heat transfer via radiant energy  Radiant energy is in the form of electromagnetic waves.
Thermal Energy. Warm Up: To shape metal into a horseshoe, the metal is heated in a fire. Why will a horseshoe bend when it’s very hot, but not after it.
Thermodynamics Thermodynamics is a branch of physics concerned with heat and temperature and their relation to energy and work.
Topic 5 Energy. Energy is the ability to do work or cause change Kinetic energy: energy of motion  faster objects have more kinetic energy Temperature.
Chapter 15 Thermodynamics Thermodynamic Systems and Their Surroundings Thermodynamics is the branch of physics that is built upon the fundamental.
Chapter 11 Thermodynamics Heat and Work and Internal Energy o Heat = Work and therefore can be converted back and forth o Work  heat if work.
Physical Science Heat and Matter. Matter Anything that occupies space and has mass Ex. Air Law of Conservation of Matter Matter is neither created or.
Chapter 15 Thermodynamics Thermodynamic Systems and Their Surroundings Thermodynamics is the branch of physics that is built upon the fundamental.
Thermal Energy Chapter THERMAL ENERGY & MATTER Work and Heat- work is never 100% efficient. Some is always lost to heat.
Thermal Energy Chapter 6. Describe things you do to make yourself feel warmer or cooler.
Thermodynamics. Thermodynamics “Movement of Heat” The study of heat and its transformation to mechanical energy. Applications –R–R–R–Refrigerators –H–H–H–Heat.
Second law of thermodynamics. The Second Law of Thermodynamics.
Physical Science Heat and Thermodynamics Chapter 16 Section Two.
Heat and Temperature. Let’s Review - According to the kinetic theory of matter, all matter is made up of tiny particles – called atoms or molecules. -
Investigation One.  The term used to describe the total of all the energy within a substance.  Heat is also known as thermal energy.  Includes both.
Chapter 16 Thermal Energy & Heat.  Objectives:  1. Explain how heat and work transfer energy  2. Relate thermal energy to the motion of particles that.
Lecture 5 Heat Transfer –Conduction –Convection –Radiation Phase Changes.
Thermal Energy That’s so hot.. All matter is made of tiny little particles (atoms and molecules) All matter is made of tiny little particles (atoms and.
Heat transfer mechanism Dhivagar R Lecture 1 1. MECHANISMS OF HEAT TRANSFER Heat can be transferred in three different ways: conduction, convection, and.
Physics 141Mechanics Lecture 24 Heat and Temperature Yongli Gao So far we have concentrated on mechanical energy, including potential and kinetic energy.
15.1 Thermodynamic Systems and Their Surroundings
Chapter 5 – Thermal Energy
Change of Phase Chapter 23.
Thermodynamics Chapter 15.
The Laws of Thermodynamics
An introduction to thermodynamics
Heat and Thermodynamics
Chapter 18,19and20 Thermodynamics.
Unit 2 Heat and temperature.
Presentation transcript:

Evaporation and condensation Individual molecules can change phase any time Evaporation: Energy required to overcome phase cohesion Higher energy molecules near the surface can then escape Condensation: Gas molecules near the surface lose KE to liquid molecules and merge

Ways to Increase Evaporation Rate Increase temperature Kinetic energy increases which increases the number of high-energy molecules that can escape from liquid state Increase surface area of liquid Increases the likelihood of molecules escaping to air Remove water vapor from surface of the liquid Prevents return of vapor molecules to liquid state Reduce pressure on liquid Reduces one of the forces holding molecules in liquid state

Capacity at present temperature Relative Humidity Ratio of how much water vapor is in the air to how much water vapor could be in the air at a certain temperature Expressed as a percentage Water vapor in air Capacity at present temperature Relative Humidity = X 100 %

Heat Transfer

Heat flow Three mechanisms for heat transfer due to a temperature difference Conduction Convection Radiation Natural flow is always from higher temperature regions to cooler ones

Conduction Heat flowing through matter Mechanism Hotter atoms collide with cooler ones, transferring some of their energy Direct physical contact required; cannot occur in a vacuum Poor conductors = insulators (Styrofoam, wool, air…)

Conduction is the flow of heat directly through a physical material.

Experimentally, it is found that the amount of heat Q that flows through a rod: increases proportionally to the cross-sectional area A increases proportionally to the temperature difference from one end to the other increases steadily with time decreases with the length of the rod

16-6 Conduction, Convection, and Radiation Combining, we find: The constant k is called the thermal conductivity of the rod.

Some typical thermal conductivities: Substances with high thermal conductivities are good conductors of heat; those with low thermal conductivities are good insulators.

Convection Energy transfer through the bulk motion of hot material Examples Space heater Gas furnace (forced) Natural convection mechanism - “hot air rises”

Convection is the flow of fluid due to a difference in temperatures, such as warm air rising. The fluid “carries” the heat with it as it moves.

Radiation Radiant energy - energy associated with electromagnetic waves Can operate through a vacuum All objects emit and absorb radiation Temperature determines Emission rate Intensity of emitted light Type of radiation given off Temperature determined by balance between rates of emission and absorption Example: Global warming

Electromagnetic Spectrum Transverse waves Regenerating co-oscillation of electric and magnetic fields Electric, magnetic and velocity vectors mutually perpendicular Form when electric charge is accelerated by external force Frequency depends on acceleration of charge Greater the acceleration, higher the frequency

Blackbody radiation Blackbody Increasing temperature Ideal absorber/emitter of light Radiation originates from oscillation of near-surface charges Increasing temperature Amount of radiation increases Peak in emission spectrum moves to higher frequency Spectrum of the Sun

All objects give off energy in the form of radiation, as electromagnetic waves – infrared, visible light, ultraviolet – which, unlike conduction and convection, can transport heat through a vacuum. Objects that are hot enough will glow – first red, then yellow, white, and blue. Objects at body temperature radiate in the infrared, and can be seen with night vision binoculars.

The amount of energy radiated by an object due to its temperature is proportional to its surface area and also to the fourth (!) power of its temperature. It also depends on the emissivity, which is a number between 0 and 1 that indicates how effective a radiator the object is; a perfect radiator would have an emissivity of 1.

Thermodynamics

Thermodynamics The study of heat and its relationship to mechanical and other forms of energy Thermodynamic analysis includes System Surroundings (everything else) Internal energy (the total internal potential and kinetic energy of the object in question) Heat engines - devices converting heat into mechanical energy

The Zeroth Law of Thermodynamics If object A is in thermal equilibrium with object C, and object B is separately in thermal equilibrium with object C, then objects A and B will be in thermal equilibrium if they are placed in thermal contact.

The First Law of Thermodynamics The first law of thermodynamics is a statement of the conservation of energy. If a system’s volume is constant, and heat is added, its internal energy increases.

The First Law of Thermodynamics If a system does work on the external world, and no heat is added, its internal energy decreases.

The First Law of Thermodynamics Combining these gives the first law of thermodynamics. The change in a system’s internal energy is related to the heat Q and the work W as follows: It is vital to keep track of the signs of Q and W.

The First Law of Thermodynamics The internal energy of the system depends only on its temperature. The work done and the heat added, however, depend on the details of the process involved.

The Second Law of Thermodynamics We observe that heat always flows spontaneously from a warmer object to a cooler one, although the opposite would not violate the conservation of energy. This direction of heat flow is one of the ways of expressing the second law of thermodynamics: When objects of different temperatures are brought into thermal contact, the spontaneous flow of heat that results is always from the high temperature object to the low temperature object. Spontaneous heat flow never proceeds in the reverse direction.

Refrigerators, Air Conditioners, and Heat Pumps While heat will flow spontaneously only from a higher temperature to a lower one, it can be made to flow the other way if work is done on the system. Refrigerators, air conditioners, and heat pumps all use work to transfer heat from a cold object to a hot object.

Refrigerators, Air Conditioners, and Heat Pumps If we compare the heat engine and the refrigerator, we see that the refrigerator is basically a heat engine running backwards – it uses work to extract heat from the cold reservoir (the inside of the refrigerator) and exhausts to the kitchen.

Refrigerators, Air Conditioners, and Heat Pumps An air conditioner is essentially identical to a refrigerator; the cold reservoir is the interior of the house or other space being cooled, and the hot reservoir is outdoors. Exhausting an air conditioner within the house will result in the house becoming warmer, just as keeping the refrigerator door open will result in the kitchen becoming warmer.

Refrigerators, Air Conditioners, and Heat Pumps Finally, a heat pump is the same as an air conditioner, except with the reservoirs reversed. Heat is removed from the cold reservoir outside, and exhausted into the house, keeping it warm. Note that the work the pump does actually contributes to the desired result (a warmer house) in this case.

Entropy For this definition to be valid, the heat transfer must be reversible. In a reversible heat engine, it can be shown that the entropy does not change.

Second law: Entropy Real process = irreversible process Measure of disorder = entropy Second law, in these terms: The total entropy of the Universe continually increases Natural processes degrade coherent, useful energy Available energy of the Universe diminishing Eventually: “heat death” of the Universe Direction of natural processes Toward more disorder Spilled milk will never “unspill” back into the glass!

18-8 Entropy A real engine will operate at a lower efficiency than a reversible engine; this means that less heat is converted to work. Therefore, Any irreversible process results in an increase of entropy.

Entropy To generalize: The total entropy of the universe increases whenever an irreversible process occurs. The total entropy of the universe is unchanged whenever a reversible process occurs. Since all real processes are irreversible, the entropy of the universe continually increases. If entropy decreases in a system due to work being done on it, a greater increase in entropy occurs outside the system.

18-8 Entropy As the total entropy of the universe increases, its ability to do work decreases. The excess heat exhausted during an irreversible process cannot be recovered; doing that would require a decrease in entropy, which is not possible.

18-9 Order, Disorder, and Entropy Entropy can be thought of as the increase in disorder in the universe. In this diagram, the end state is less ordered than the initial state – the separation between low and high temperature areas has been lost.

18-9 Order, Disorder, and Entropy If we look at the ultimate fate of the universe in light of the continual increase in entropy, we might envision a future in which the entire universe would have come to the same temperature. At this point, it would no longer be possible to do any work, nor would any type of life be possible. This is referred to as the “heat death” of the universe.

18-9 Order, Disorder, and Entropy So if entropy is continually increasing, how is life possible? How is it that species can evolve into ever more complex forms? Doesn’t this violate the second law of thermodynamics? No – life and increasing complexity can exist because they use energy to drive their functioning. The overall entropy of the universe is still increasing. When a living entity stops using energy, it dies, and its entropy can increase rather quickly.

The Third Law of Thermodynamics Absolute zero is a temperature that an object can get arbitrarily close to, but never attain. Temperatures as low as 2.0 x 10-8 K have been achieved in the laboratory, but absolute zero will remain ever elusive – there is simply nowhere to “put” that last little bit of energy. This is the third law of thermodynamics: It is impossible to lower the temperature of an object to absolute zero in a finite number of steps.

Q1. Substance A has a higher specific heat than substance B Q1. Substance A has a higher specific heat than substance B. Which requires the most energy to heat equal masses of A and B to the same temperature? A) Substance A B) Substance B C) Both require the same amount of heat. D) Answer depends on the density of each substance.

Q2. Anytime a temperature difference occurs, you can expect A) cold to move to where it is warmer. B) energy movement from higher temperature regions. C) no energy movement unless it is warm enough, at least above the freezing temperature. D) energy movement flowing slowly from cold to warmer regions.

Q3. As a solid goes through a phase change to a liquid, heat is absorbed and the temperature A) increases. B) decreases. C) remains the same. D) fluctuates.

Q4. The transfer of energy from molecule to molecule is called A) convection. B) radiation. C) conduction. D) equilibrium.