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First Law of Thermodynamics
Law of Conservation energy
First Law
Internal energy of a system can be increased by adding energy to the system (heat is added/subtracted) OR by doing work on the system
Law of Conservation energy
Energy can’t be gained or lost without the intervention of an outside system
Doing work & By heat
Energy Transfers Occur because
No
Can Heat turn into Work
Yes
Can Work turn into Heat
+
In PV diagram if the volume goes left to right, the work is
-
In PV diagram if the volume goes right to left, the work is
Isobaric
Pressure stays constant for the cycle
Isovolumetric/Isometric/Isochoric
Volume stays constant
Isothermal
Temperature stays the same
Adiabatic
No heat
Cycles
When you move in the form of a shape on a PV diagram and return to your original pressure & volume
path dependent
If work and heat are not state dependent functions, what kind of functions are they
area enclosed by the path
What is the net work done per cycle by a gas in a PV diagram
Free Expansion Process
All energy is 0. There is energy that is just constant because the medium isn’t conducive to a change in energy like space
Isothermal
What thermal process is the Free Expansion Process
Isolated System
Does not mess with its surroundings so energy is constant
Open System
Energy transfer does take place and work is done
Pressure*Area
How to get the force from a PV diagram
Pressure
How much force is being exerted on a surface per square meter
area under the curve for each
For finding work, every single line on a cycle has its OWN work value, so you have to calculate the
Ideal Gas
A gas that moves free of intermolecular actions of the gas, if its behavior is not affected by other gas molecules
low pressures and high temperatures
*All gasses behave as ideal gasses at
molecules move randomly exerting no long-range force on one another and volume is basically 0
Two characteristics of ideal gases are
Mass/Molar Mass
Moles Formula
Avogadro’s Number
Number of particles in a mole
Particles
Moles * Avogadro’s Number
Isothermal
W = nRT ln(Vf/Vo) only works if the thermal process is
Isothermal
Work = (P)(∆V) only works in
Gauge Pressure
How much more pressure than atmospheric pressure a gas has (it means how far above 1.015 x 105 Pa the pressure value is)
thermal equilibrium
The process of work (force) happens very slowly so its assumed to be in
Temperature and pressure
If a gas in a cylinder is compressed by a piston then assume every part of the gas has the same
Average pressure
(Isothermal I believe) In the work equation, if pressure changes then use the
Kinetic Theory of Gases
Number of molecules in the gas is large and the average separation (the distance between them) is larger than their dimensions
Move randomly and obey Newton’s Laws of Motion
What two things do the molecules in a kinetic theory of gases do
Elastic Collision
Is a collision when no kinetic energy is lost
Identical
The gases here are pure substances in Kinetic Theory of Gases, meaning molecules are
The amount of energy to raise 1 mole of an ideal gas by 1 degree celsius/kelvin
The molar specific heat at constant volume (Cv) for an ideal gas
3/2R
Monatomic: Cv =
5/2R
Diatomic: Cv =
3R
Polyatomic: Cv =
More energy causing smaller temperature differences compared to monatomic
Gases with higher molar specific heat requires
Degrees of Freedom
Each way a gas (molecules) can store energy
3 degrees of freedom in velocity (x, y, z)
Why is monatomic 3/2R because it has
Mean Free Path
Average distance that a molecule will travel before it collides with the wall or another molecule
Temperature decreases
For adiabats going to the right (expanding)
right/up
If it says expansion, that means it’s going to the____/_____ for isobaric & isochoric respectively
