Heat, Temperature, Heat, Temperature, Heat Transfer & Heat Transfer &

ThermodynamicsThermodynamics

Heat vs. Heat vs. TemperatureTemperature

HeatHeat A form of energyA form of energy Measured in Measured in

calories or Joules calories or Joules There is no There is no

“coldness” energy“coldness” energy Any object with Any object with

temperature above temperature above zero Kelvin has heat zero Kelvin has heat energyenergy

TemperaturTemperaturee

Avg. Kinetic Energy Avg. Kinetic Energy of the particlesof the particles

Measured in Measured in C, C, F, F, K, RK, R

““hot” & “cold are hot” & “cold are relative termsrelative terms

Absolute zero is Absolute zero is zero Kelvinzero Kelvin

Heat TransferHeat Transfer(3 methods)(3 methods)

1. Conduction - requires direct contact or particle to particle transfer of energy; usually occurs in solids

2. Convection - heat moves in currents; only happens in fluid states of matter

3. Radiation - heat waves travel through empty space, no matter needed; IR

Thermal EquilibriumThermal Equilibrium

A system is in thermal A system is in thermal equilibrium when all of its parts equilibrium when all of its parts are at the same temperature.are at the same temperature.

Heat transfers only from Heat transfers only from high high to lowto low temperatures and only temperatures and only until thermal equilibrium is until thermal equilibrium is reached.reached.

Temperature ScalesTemperature Scales There are four temperature scales – There are four temperature scales –

Celsius (Centigrade), Kelvin, Celsius (Centigrade), Kelvin, Fahrenheit, & RankineFahrenheit, & Rankine

Celsius, Celsius, C C – metric temp. scale– metric temp. scale Kelvin, K – metric absolute zero temp. Kelvin, K – metric absolute zero temp.

scalescale Fahrenheit, Fahrenheit, F – customary (english) F – customary (english)

temp. scaletemp. scale Rankine, R – english absolute zero Rankine, R – english absolute zero

temp scaletemp scale

Comparing Comparing Temperature ScalesTemperature Scales

Celsius - Freezing = 0°C, Boiling = 100°CCelsius - Freezing = 0°C, Boiling = 100°C Kelvin - Freezing = 273K, Boiling = 373KKelvin - Freezing = 273K, Boiling = 373K Fahrenheit- Freezing = 32°F, Boiling = 212°F Fahrenheit- Freezing = 32°F, Boiling = 212°F

Conversions between Scales°F = 1.8 *°C+32 K = °C + 273

All temperatures listed are for water

Change of StateChange of StateT

emp

° C

Increasing Heat Energy (Joules)

-20

100

0

ice

water

steam

melting

vaporization

condensation

freezing

As heat is added to a substance it will either be absorbed to raise the temperature OR to change the state of matter.

It can NEVER do both at the same time.

Temperature will NOT change during a phase change!

Heat of vaporization

Heat of fusion

Specific HeatSpecific Heat

The amount of heat energy needed to raise the temperature of 1 gram of substance by 1°C.

Substances with lower specific heats change temperature faster.

Symbol : c units : cal/g°C or J/kg°C

For water: c = 1 cal/g°C = 4.18 J/g°C = 4180 J/kg°C

Latent HeatLatent Heat The amount of heat energy required to change the state of 1 gram of substance.

Heat of fusion - latent heat for changes between the solid and liquid phases.

Lf =80 cal/g for water

Heat of vaporization - latent heat for changes between the liquid and gas phases. Lv =540 cal/g for water

Heat CalculationsHeat Calculations

Q = mcΔT

Temperature Change

Q = heat absorbed or released

m = mass of substance being heated

c = specific heat of substance

ΔT = change in temperature

Phase Change

Q = mLQ = heat absorbed or released

m = mass of substance changing phase

L = latent heat of substance

Lf = heat of fusion (liquid solid)

Lv = heat of vaporization (liquid gas)

ThermodynamicsThermodynamics The study of changes in thermal The study of changes in thermal

properties of matterproperties of matter Follows Law of Conservation of Follows Law of Conservation of

EnergyEnergy 11stst Law Law – the total increase in – the total increase in

the thermal energy of a system the thermal energy of a system is the sum of the work done on it is the sum of the work done on it and the heat added to itand the heat added to it

22ndnd Law Law – natural processes tend – natural processes tend to increase the total entropy to increase the total entropy (disorder) of the universe.(disorder) of the universe.

11stst Law of Law of ThermodynamicsThermodynamics

The total increase in the thermal energy of a system is the sum of the work done on it and the heat added to it.

ΔU = W + Q

ΔU = change in the thermal energy of the system

W = work done on the system (W = Fd or W=ΔK)

Q = heat added to the system

(Q is + if absorbed, Q is – if released)

*All measured in Joules*

Heat enginesHeat engines

Convert thermal energy to Convert thermal energy to mechanical energymechanical energy

Require high temp heat source Require high temp heat source and low temp heat sink. (Takes and low temp heat sink. (Takes advantage of heat transfer advantage of heat transfer process)process)

Examples: Steam engine,Examples: Steam engine,Automobile engineAutomobile engine

Refrigerators and Heat Refrigerators and Heat PumpsPumps

It is possible to remove heat from a It is possible to remove heat from a cold environment and deposit it into a cold environment and deposit it into a warmer environment.warmer environment.

This requires an outside source of This requires an outside source of energy.energy.

Examples: Refrigerators, Examples: Refrigerators, Air conditioning unitsAir conditioning units

Heat pumps are refrigeration units Heat pumps are refrigeration units that work in either direction.that work in either direction.

22ndnd Law of Law of ThermodynamicsThermodynamics

All natural processes go in a direction that increases the total entropy of the universe.

Entropy is a measure of the disorder of a system.

If heat is added, entropy is increased.

If heat is removed, entropy is decreased.

Work with no ΔT, entropy is unchanged