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Thermodynamics is a Study of heat.
A major topic of in this field Is the Kinetic-Molecular Theory.
The kinetic-molecular theoryIs based on the assumption that
In a hot body, the particlesMove faster and thus have
More kinetic energy.
And Vise-Versa.
The overall energy of motion ofThe particles that make-up
An object is called the Thermal energy of that object.
THIS IS DIFFERENT THAN TEMPERATURE!!
What do you use to measureTemperature?
Maybe a thermometer?
An Italian physicist inventedThe very first thermometer,
Who was he?
Galileo Galilei
Temperature is the “hottness”Of an object as measured
Using a specific scale.
Heat always flows from hot to cold.
A device that measures temperature is called
A thermometer.
The choice of a temp. Scale is quite arbitrary.
One popular one was invented By Gabriel Fahrenheit.
He devised his own scale.Do you know what it is?
Duh, Fahrenheit!
His thermometer were popular, So his system was as well.
After a while a different scaleWas accepted by
Scientists.
It was called Celsius,Invented by Anders Celsius
The Celsius scale was theFirst major scale to
Place the freezing point ofWater at 0, and theBoiling point at 100.
A few correlations:
Melting ice
Normal body temp.
Boiling water
0°C 32°F
37°C 98.6°F
100°C 212°F
The newest temp. scaleIs the Kelvin scale.
The Kelvin scale is the SI Scale accepted by scientists
It was invented by William Thomson, Lord Kelvin
The difference between the Celsius and Kelvin scales
Is very small.
It has to deal with the Zero point.
0 Kelvin is the absolute zero,Or -273.15 °C
At absolute zero, allKinetic energy stops!
Though theoretically possible, It can never be reached,
So far.
A few conversions, shall we.
°F = 9/5 °C + 32
°C = 5/9 X (°F – 32)
K = °C + 273
Let’s try some…
163°C = ? °F
50 K = ? °C
-40 °F = ? °C
325°F
-223°C
-40°C
Convection is the transferOf heat by means of
Motion in a fluid.
Radiation is the transferOf energy by electromagnetic
Waves.
Specific heat is the amount ofEnergy that must be added to a
Material to raise the temperatureOf a unit mass one Temperature unit.
Q = mCΔT
Q = heatC = specific heat
A 0.4 kg block of iron is Heated from 295 K to 325 K.
How much heat had to be Transferred to the iron?
Q = 540 J
Thermal equilibrium is a state Where the rate of energy Transfer between bodies
Becomes equal and the bodiesWill thus have the same
Temperature.
Conduction is the transfer of Kinetic energy when
Particles collide.
There are 4 states of matterWhat are they?
Solid LiquidGas Plasma
So how can you go fromOne state to another?
By changing the temperature.
Heating or cooling can cause:Boiling, freezing, sublimation,
Etc.
The energy required to melt a Substance goes into
Rearranging the molecules.
The heat of fusion is the energy Per unit mass transferred in Order to change a substance
From liquid to solid at a Constant temperature
And pressure.
The heat of vaporization is the Energy per unit mass
Transferred in order to change From a liquid to a vaporAt constant temperature
And pressure.
Latent heat is the energy per unit Mass that is transferred duringA phase change of a substance.
There are formulas to find The amount of heat used
By the heats of fusion and Vaporization.
Q = mHfQ = mHv
Catherine is asked to melt 0.1 kg of ice at its melting
Point and warm the resultingWater to 20.0 °C. How Much heat is needed?
Q = 41.8 kJ
First Law of Thermodynamics
The energy of the universe is constant.
(comes from the law of conservation of energy)
The first law of thermodynamicsStates that the total increaseIn thermal energy of a systemIs the sum of the heat added
To it and the work done on it.
Your book says it like this…
ΔU = Q - WU = Internal energy
Q = Heat W = Work
Q > 0 Energy added to system by heat
Internal energy increases
Q < 0 Energy removed from system by heat
Internal energy decreases
Q = 0 No transfer of energy by heat
No internal energy change
W > 0 Work done by system
Internal energy decreases
W < 0 Work done on system
Internal energy increases
W = 0 No work done No internal energy change
Signs of Q & W for a system
A total of 135 J of work is done on A gaseous refrigerant as it
Undergoes compression. If the Internal energy of the gas increases
By 114J during the process, whatIs the total amount of energy
Transferred by heat? Has energyBeen added to or removed from
The system?Q = -21 J
The second law of thermodynamicsStates that the entropy of
The universe is always Maintained or increased.
Entropy is the measure of Disorder of a system.
No machine can be made that Only absorbs energy by heat
And then entirely transfers theEnergy out of the engine by An equal amount of work.
The second law can Also be stated as…
Increasing disorder reducesThe energy available for work.
Greater disorder means there Is less energy to do work.
Entropy can increase orDecrease within a system.
ΔS = QT
S = EntropyQ = Heat
T = Temperature in Kelvins
