Internal Properties of Matter - Foundationokanagancollegefoundationrefrigeration.pbworks.com/f/Principles of... · Internal Properties of Matter Topics for Discussion •Law of Conservation

Internal Properties of MatterInternal Properties of Matter

Topics for Discussion

•Law of Conservation of Energy

•Types of Internal Energy•Types of Internal Energy

•Physical States of Matter

•Temperature

•Heat and the convertibility of heat and work

Conservation of EnergyConservation of Energy

•The law of conservation of energy states that

energy cannot be created or destroyed, it can only

be converted from one form to another.

•Work done on an object changes its levels of

external kinetic and potential energy.

•Therefore the amount of work done on an object

changes its energy level. Energy can be described as

the amount of work stored within a substance.


•When work is done on an object, some of the work

is converted into energy that is stored within its

molecular structure for use at a later time.

•In addition to these external or mechanical forms of

energy, an object also possesses energy in a number

of internal forms.

•This internal energy is stored within the molecular

structure of substances, and can be released as work


•Work, external energy, and internal energy are all

interchangeable. No matter what types of energy are

stored within an object.

•Electrical energy can be converted to thermal

energy in an electric heater. Electrical energy can be

converted to mechanical energy in an electric motor.

Chemical energy can be converted to electrical

energy in batteries to power our portable devices.

ThermodynamicsThermodynamics

•Thermodynamics is the study of a substance’s

energy-related properties and processes.

•Thermodynamics quantifies the changes in energy •Thermodynamics quantifies the changes in energy

that occur as heat is transferred from one object to

another.

•In the HVAC-R field the processes that we utilize

generate changes in the internal and external energy

levels in substances within the field.

Types of Internal EnergyTypes of Internal Energy

•Internal energy is the energy contained within a

substance by virtue of the motions and forces

between its individual atoms and molecules.

•Internal kinetic energy is the energy of molecular

motion. Molecules are always in a state of rapid and

constant vibration.

•The rate of these vibrations depends on the amount

of internal kinetic energy that the substance has.


•One method of altering the internal kinetic energy

of a substance is to transfer thermal energy to it.

•Whenever thermal energy transfers into a •Whenever thermal energy transfers into a

substance, it increases the intensity of the molecular

vibrations. And when ever thermal energy is

removed from a substance it reduces a substances

kinetic energy, and slows the vibrations.


•A relationship exists between the kinetic energy

content of a substance, its level of molecular

vibrations, and its temperature.

•The temperature of a substance is an index of the

average velocity of molecular vibrations, and

therefore the amount of kinetic energy stored in its

molecules.

•At absolute zero internal kinetic energy is zero.

Internal Potential EnergyInternal Potential Energy

•The molecules of a substance are held together by

cohesion. Cohesion is the tendency of matter to hold

itself together be attractive forces between

molecules.molecules.

•As two molecules or atoms approach each other,

their internal potential energies decrease towards a

minimum value.

•This min value is called the equilibrium distance.


•Increasing or decreasing the equilibrium distance

requires the performance of work.

•Work can push the molecules closer together or pull •Work can push the molecules closer together or pull

them farther apart.

•Whenever work is done to move molecules closer

together, the applied force must overcome a rapidly

increasing force reactive force called compressive

elasticity.


•Similarly any work done to increase the distance

between the molecules is opposed by cohesive

forces.

•Cohesive forces are greatest in solid, much weaker

in liquids and nonexistent in gases.

•Since molecules are bound to one another by

cohesive forces, internal work must be done in order

to further separate them.


•When a material expands, contracts or changes its

physical state, a rearrangement of its molecules

takes place in response to the work or change in

energy.energy.

•These changes alter the average distance between

molecules within a substance. Therefore the work

done, or energy transfer generates changes in the

quantity of stored internal potential energy.


•This change in the stored energy of the substance

has no influence on the intensity of the molecular

vibrations. Therefore the kinetic energy stays

constant during potential energy altering processes.constant during potential energy altering processes.

•Kinetic energy = energy in motion = molecular

movement = temperature = sensible heat.

•Potential energy = stored energy = physical state =

state change = latent heat.

Physical States of MatterPhysical States of Matter

•Many chemical compositions, under the proper

conditions of pressure and temperature, can exist in

three distinct phases, or states of matter.

•A material in its solid phase has relatively small

amounts of internal potential and kinetic energies.

•Its molecules are generally positioned at their

equilibrium distance, arranged in well formed

crystalline structures.


•The molecules of a substance in its liquid phase

have more kinetic and potential energy than they

have when they are in their solid phase.

•With an increase in kinetic energy absorbed by a

solid substance, increases the molecular vibration

increasing the temperature of the substance.

•An additional increase in potential energy absorbed

causes the molecules to break their cohesive bonds.


•When a solid breaks its crystalline structure bonds,

the material begins to flow.

•The ability for a substance to flow is a characteristic •The ability for a substance to flow is a characteristic

of all fluids, no matter if they are liquids, vapors or

gases.

•Consequently liquids cannot retain their shape and

are forced to assume the shape of the vessel in

which they are contained.


•Liquids are also considered incompressible because

their density and molecular spacing are nearly the

same as they are in the solid phase.

•The incompressibility and flow characteristics of a

liquid permit forces to be transmitted equally in all

directions.

•Pascal’s law demonstrates this characteristic,

utilized in hydraulic systems.


•As a liquid substance absorbs more heat, its

molecules vibrate with greater forces.

•This additional energy overcomes all restraining •This additional energy overcomes all restraining

forces between its molecules, eliminating the

molecules cohesive bonds.

•The gas molecules are free to fly about at high

velocities, for this reason a gas cannot retain its size

or shape.


•The lack of cohesive structure means that gases are

readily compressible.

•The also move to maintain the greatest possible •The also move to maintain the greatest possible

distance between the molecules, completely filling

the vessel in which they are contained.

•If a gas is not contained in sealed contained, it will

escape and diffuse into the surrounding ambient.


•A vapor is a gas that exists at conditions that permit

it be easily returned to its liquid state.

•As a liquid absorbs sufficient potential energy, some •As a liquid absorbs sufficient potential energy, some

of the molecules will break free of their cohesive

bonds and turn to a vapor.

•The molecules that have sufficient energy to break

their bonds and remain free of the liquid surface are

classified as a vapor.


•As more energy is added to a vapor, its internal

kinetic energy increases, this raises the temperature

of the vapor making the molecules move faster.

•In this condition it becomes more difficult to return

the molecules to their liquid state.

•When the temperature of a vapor is raised to a level

much higher than the temp at which it changed state

from a liquid, the molecules are classified a gas.

TemperatureTemperature

•The temperature of a substance is a measure of the

amount of kinetic energy it contains.

•Temperature is a property of a substance that •Temperature is a property of a substance that

measures its thermal intensity. Thermal intensity is

an indication of the average molecular velocity

within a substance.

•Temperature is also used to indicate the direction of

thermal energy transfer.

TemperatureTemperature

•Thermometers are used to measure temperature,

their operation depends on the characteristic of

liquids to expand when their temperature is

increased.increased.

•The coefficient of expansion is the rate at which a

substance expands when its temperature changes.

•Mercury thermometers are more accurate than

alcohol because their coefficient of expansion is

more consistent through a greater temp range.

HeatHeat

•Heat is the transfer of energy produced by a

temperature change.

•Heat is the thermal counterpart of energy transfer •Heat is the thermal counterpart of energy transfer

by work in mechanical systems, where work is

transfer of energy by a force that moves a mass

through a distance.

•Heat is the transfer of energy from one object to

another caused by a thermal force created by a

temperature difference between the objects.

HeatHeat

•Heat transfers internal kinetic energy from the

molecules of the warmer object to those of the

cooler object.

•This energy transfer reduces the kinetic energy level

of the molecules in the warmer object, producing a

corresponding decrease in its temperature.

•Simultaneously the cooler objects kinetic energy is

increasing.

HeatHeat

•Energy transfers that affect the temperature of

objects are called heat.

•Although heat transfer occurs primarily in response •Although heat transfer occurs primarily in response

to temperature difference, it can also be brought

about by friction forces.

•Friction forces are conflicts and interactions that

occur on the molecular level as objects move relative

to one another.

HeatHeat

•These interactions generate changes in the kinetic

energy levels of the molecules located at the

interface between two surfaces.

•The elastic stretching and snapping of the molecules

sliding past each other changes their velocities and

the temperatures of the objects.

•This change in thermal energy is a conversion

process where some of the work done is stored

energy in the substance.

HeatHeat

•There is a technical difference between the terms

thermal energy and heat.

•Thermal energy is the ability if an object to do work •Thermal energy is the ability if an object to do work

that results from energy contained within its

molecule structure.

•Heat is the actual condition of energy being

transferred, not a property of a substance.

Heat TransferHeat Transfer

•The phrase heat transfer is often used to describe

the energy transfer, although the term heat

incorporates the transfer aspect of the energy

movement.movement.

•Thermal energy will be transmitted from one object

to another when they are at different temperatures.

•The following three relationships govern the flow of

thermal energy between objects.


1. Heat flows from a higher temperature to a lower

temperature

2. Whenever an object is in thermal equilibrium 2. Whenever an object is in thermal equilibrium

with its surroundings, both will have the same

temperature. Therefore no thermal energy will

transfer between the objects.

3. Heat transfer cannot spontaneously occur from

cool to warm, without work done on the system.


• A mechanical refrigeration system is an example

of a system that moves heat from a cooler

location to a warmer one.

• Since heat is energy, and cannot be consumed or

destroyed in any process, all of the thermal

energy that leaves one object must be absorbed

by other objects, or substances.

Conduction Heat TransferConduction Heat Transfer

• Energy transfer by conduction requires physical

contact exist between the objects transferring

heat.

• Therefore, this mode is only applicable between

solids and motionless liquids.

• The contact allows kinetic energy to physically

transfer from molecule to molecule.


• As the higher energy level molecules of the

warmer object collide with the slower moving

molecules of the cooler object, an energy transfer

occurs between the objects.occurs between the objects.

• This energy transfer occurs along the interface

where the objects are touching, as the faster

molecules collide with the slower molecules the

faster molecules slow down as the slower

molecules now speed up.


• Some materials are better at conducting heat than

others, Iron, Copper, Silver, Gold and similar

metals are good conductors of heat.

• The increase in the rate of heat transfer in good

thermal conductors occurs because these

materials employ two methods to transfer kinetic

energy.

• In addition to energy transfer due to collisions,

energy can also transfer due to free electrons.


• In addition to energy transfer due to collisions,

energy can also transfer due to free electrons.

• Free electrons are valance electrons within • Free electrons are valance electrons within

material that break free from the orbits of their

parent atoms when they absorb sufficient thermal

or electrical energy.

• These electrons are then free to move through the

material, transferring their excess kinetic energy.


• Conversely, materials that are insulators can only

conduct energy by molecular vibrations to

adjoining molecules.

• The relative capacity of a material to conduct heat

is known as its thermal conductivity (k).

• Thermal conductivity is a measure of the amount

of energy that can pass through one square foot

unit of material, one inch thick, in one hour, with

1°F temperature difference. Btu/ft2/hr/°F

Convection Heat TransferConvection Heat Transfer

• Heat transfer by convection can only occur in

moving fluids. Thermal energy is moved by

currents that form within a fluid.

• Natural convection currents are generated by

changes in a fluid’s density brought about by the

expansion of the portion of the fluid being

heated.

• As a fluid is heated it expands increasing its

specific volume, becoming more buoyant.

Convection Heat TransferConvection Heat Transfer

• Heat transfer by convection can only occur in

moving fluids. Thermal energy is moved by

currents that form within a fluid.

• Natural convection currents are generated by

changes in a fluid’s density brought about by the

expansion of the portion of the fluid being

heated.

• As a fluid is heated it expands increasing its

specific volume, becoming more buoyant.

Radiation Heat TransferRadiation Heat Transfer

• Radiation heat transfer occurs between materials

at different temperatures within sight of each

other.

• By its nature radiation heat transfer does not rely

on physical contact, moving fluids, or any other

medium to exchange energy.

• Therefore heat transfer across a vacuum is only

possible by radiation.


• The term radiation indicates that the energy is

transferred between objects in the form of

electromagnetic waves.

• Electromagnetic waves of heat are very similar to

electromagnetic waves of light. They only differ in

their energy level, frequency and therefore

wavelength.

• Thermal energy waves are found in the infrared

portion on the electromagnetic spectrum.


• Whether heat waves are visible or invisible

depends on the temperature of the radiating

object.

• When electromagnetic energy waves produced by

an object are intercepted by another object, they

can be either absorbed, reflected and/or

transmitted through the intercepting material.


• When the radiant energy is absorbed the energy

in the wave increases the kinetic energy of the

molecules within the intercepting object.

• This action causes the temperature of the

absorbing material to increase, indicating heat

transfer has occurred.

• The amount of radiant energy that is absorbed,

reflected or transmitted depends on the materials

surface, texture and its colour.

Units of HeatUnits of Heat

• Heat (Q) is the transfer of energy that produces a

change in phase or temperature of an object or

material.

• Heat can be converted into work, and work can be

converted into heat.

• Imperial Units Heat = BTU & Work = FT-LBF

• Metric Units Heat = Joule & Work = Joule

Specific HeatSpecific Heat

• Specific heat is a property of a substance that

indicates the quantity of energy that is needed to

change one unit of mass one degree.

• The specific heat of any substance varies with its

temperature, generally the variance is small and

can be assumed to be constant for most calcs.

• Their specific heat changes significantly when the

substance experiences a phase change.

Sensible Heat of the SolidSensible Heat of the Solid

• Understanding internal kinetic energy starts from

the solid state at absolute zero starting point.

• As thermal energy is transferred the molecules • As thermal energy is transferred the molecules

begin to vibrate, as more energy is transferred the

molecule vibration increases raising the

temperature of the solid.

• The total temperature required to raise the solid

from absolute zero to its fusion temperature is

known as the sensible heat of the solid.

Latent Heat of FusionLatent Heat of Fusion

• As the temperature of the solid reaches its fusion

temperature, the molecules are vibrating at the

maximum intensity possible within the limits of

the rigid crystalline structure.the rigid crystalline structure.

• At the fusion temperature any additional energy

supplied to the solid causes the molecular

vibrations to be so intense that the crystalline

bonds fracture.

Sensible Heat of the LiquidSensible Heat of the Liquid

• As a solid substance begins converting into its

liquid phase, the resulting fluid remains at its

fusion temperature through the process.

• Once the state change is finished kinetic energy

can be then absorbed increasing its temperature.

• When sufficient energy is absorbed a point is

reached where the molecules have reached the

maximum velocity possible within the limits of

the liquid phase.

Sensible Heat of the LiquidSensible Heat of the Liquid

• At this point the liquid will be at it the maximum

temperature it can have, and still remain in the

liquid phase at the current pressure.

• Any additional energy will begin to produce vapor.

• The total quantity of energy supplied to a liquid to

increase its temperature from its fusion

temperature to its vaporizing temperature, is

knows as the sensible heat of the liquid.

Saturation TemperatureSaturation Temperature

• The temperature at which a fluid changes from its

liquid phase to its vapor phase or from its vapor

phase to its liquid phase, is called saturation

temperature.temperature.

• For any given ambient or pressure, the saturation

temperature is the maximum temperature at

which the substance can stay in its liquid phase, or

the minimum temperature it can stay in its vapor

phase.

Latent heat of VaporizationLatent heat of Vaporization

• As a substance changes phase from a liquid to a

vapor, its molecules acquire sufficient energy to

substantially overcome all restraining forces.

• The amount of energy required to do the internal

work necessary to overcome these restraining

forces is very great.

• Therefore the latent heat capacity of a liquid is

very high compared to a solid.

SuperheatSuperheat

• Once a liquid has been vaporized, any additional

energy or heat transfer will raise its internal

kinetic energy and its temperature.

• This heat is called the sensible of the vapor or

superheat.

• Therefore any time the temperature of a vapor is

raised above its saturation temperature, the vapor

is said to be “Superheated”

The Convertibility of Heat and WorkThe Convertibility of Heat and Work

• Work can be converted into thermal energy and

thermal energy can be converted into work.

• Work can be performed on a system to increase • Work can be performed on a system to increase

its thermal energy, or thermal energy can be used

to perform work.

• When a refrigeration compressor performs work

on the refrigerant vapor during compression, its

molecular vibrations increase raising temperature.

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Internal Properties of Matter - Foundationokanagancollegefoundationrefrigeration.pbworks.com/f/Principles of... · Internal Properties of Matter Topics for Discussion •Law of Conservation