Download Intro, KM Theory, Temp Conversion, Heat transfer Thermodynamics

THERMODYNAMICS NOTES
DAY 1 – Intro, K-M Theory, Temp Conversion, Heat transfer
Thermodynamics – Study of heat
What makes something hot or cold?
-Old idea (“Caloric”)– Hot objects possess more of an imaginary, invisible fluid called “caloric”
than cold objects.
-This theory could explain why objects expanded when they got hot
-This theory could not explain why objects got hot when rubbed together
-Because this theory can’t explain how objects respond to heat in all situations a new theory
was needed
Kinetic-Molecular Theory –
-All matter is made of made of tiny particles (atoms and molecules) that are always in motion
-Hot objects – the particles move faster, have more kinetic energy
-Cold objects – the particles move slower, have less kinetic energy
-Kinetic-Molecular Structure of Solids, Liquids, and Gases –
-The particles inside the object are attracted with electrostatic force therefore they can have not only
kinetic energy, but also potential energy
-Thermal Energy (aka Internal Energy) - is the total energy of motion of all of the particles (sum of KE
and PE) within the object
- Not all particles have the same energy. On average hotter objects have faster moving particles.
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THERMODYNAMICS NOTES
-Temperature – a rank of “hotness”, it depends on the average kinetic energy of the particles in an
object. Three different scales: Fahrenheit, Celsius, Kelvin
Example #1: Convert 32 degree Fahrenheit to Celsius. Next, convert it to Kelvin.
Example #2: Convert 100 Degrees Celsius to Fahrenheit.
Example #3: Convert 40 degrees Celsius to Kelvin.
We measure temperature with a Thermometer. As the liquid in the thermometer
heats up its particles gain kinetic energy and therefore the volume of the liquid
expands and rises.
Thermal Equilibrium – The state where the rate of energy transfer between
bodies becomes equal and the bodies will be at the same temperature.
-In other words, when a hot object and a cold object come into contact, they will eventually reach a
common temperature. Heat will flow from the hot object to the cold object, never from the cold object
to the hot object. Total Energy between the two objects must remain the same!
Heat and Thermal Energy Transfer –
Conduction – “Heating via contact”. The particles of two materials literally collide into each other.
Convection – “Heating via air/liquid currents”. Like a ‘convection’ oven.
Radiation – Transferring energy via electromagnetic waves. Like the sun’s energy.
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THERMODYNAMICS NOTES
DAY 2 – State Change, Heat, Specific Heat
Changing State – Moving from solid to liquid to gas
-If you start with a solid and add heat (energy) the particles in the solid will move more rapidly. At
certain points the forces on the motion the particles have will overcome the forces holding the particles
together. The solid will become a liquid. If you continue to apply heat, the solid will become a gas as its
particles move even more freely.
Heat – The energy transferred between objects because of the temperature difference. Because heat is
energy we can measure it in Joules.
Melting Point –The temperature at which a solid object becomes a liquid.
Boiling Point – The temperature at which a liquid object becomes a gas.
Heat of fusion – The temperature needed to melt 1 kg of a substance.
Heat of vaporization – The temperature needed to vaporize (make steam) out of 1 kg of a liquid.
Heat Required to Melt an Object = mass x Heat of fusion
Heat Required to Vaporize = mass x Heat of vaporization
Specific Heat – amount of energy that must be added to the material to raise the temperature one kg of
the object by one degree
Heat Transferred (Amount of heat gained or lost by an object) = mass x specific heat x change in temp
*For now, Specific Heat will be given in a table.
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THERMODYNAMICS NOTES
DAY 3 – The Laws of Thermodynamics, Absolute Zero, Thermal
Expansion
Laws of Thermodynamics
The four laws of thermodynamics are:
Zeroth law of thermodynamics: If two systems are in thermal equilibrium with a third system, they must
be in thermal equilibrium with each other. This law helps define the notion of temperature.
First law of thermodynamics: Heat is a form of energy. Because energy is conserved, the internal energy
of a system changes as heat flows in or out of it. Equivalently, perpetual motion machines of the first
kind are impossible.
Second law of thermodynamics: The entropy of any isolated system not in thermal equilibrium almost
always increases. Closed systems spontaneously evolve towards thermal equilibrium—the state of
maximum entropy of the system—in a process known as "thermalization". Equivalently, perpetual
motion machines of the second kind are impossible.
Third law of thermodynamics: The entropy of a system approaches a constant value as the temperature
approaches zero. The entropy of a system at absolute zero is typically zero, and in all cases is
determined only by the number of different ground states it has.
Absolute Zero - the temperature below which it is impossible to cool an object.
Thermal Expansion – Most substances expand when heated.
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