Week 1 Flashcards
(20 cards)
What is the 1st law of thermodynamics?
ΔU = ΔW + ΔQ
Energy is always conserved, heat and work are both forms of energy.
What is the 0th Law of thermodynamics?
If two systems are separately in thermal equilibrium with a third system, all three bodies are in equilibrium (i.e all the same temperature).
What is the 2nd law of thermodynamics?
- Heat cannot be converted into work with 100% efficiency
- It is not possible to transfer heat from a colder body to a hotter body.
- Entropy of the universe cannot decrease (giving the arrow of time).
What is the 3rd law of thermodynamics?
You cannot cool anything to absolute zero.
What is the thermodynamic limit?
A system with a large number of particles, or after a long time, so fluctuations of individual particle movement is small compared to the average of the system.
What is a thermodynamic system?
A body that has well defined interactions with it’s surroundings and is considered separate from them.
where system + surroundings = universe.
What is thermal equilibrium?
when a system’s macroscopic observables (e.g pressure, temperature) ceases to change with time.
what means two bodies are in thermal equilibrium with each other?
If no heat flows between then (when they are connected in a way that it could)
What is an extensive and intensive variable?
Give examples of both.
Extensive - scales with the size of the system.
e.g. volume, entropy, number of particles, magnetic moment.
Intensive - independent to the size of the system.
e.g. temperature, number/entropy density, pressure.
What is a state function, give examples and how could you prove it?
A state function assumes a unique value for each equilibrium state of the system ( the state of the function is path independent of how it got there).
e.g volume, pressure, temperature, internal energy
State functions must have exact differentials.
What are the properties of non-state functions and give example?
A non-state function is path dependant of the change.
e.g. heat and work.
they have inexact differentials (represented with a bar)
define Heat
heat - is energy in transfer between one system and another/ the surroundings.
dQ is the heat supplied TO the system.
define work
work - the change in energy of a system affected by changing its parameters
dW is the work done ON the system
define internal energy
Interal energy, U - the sum of all the components of energy in a system
Is work done on/by a gas when it is compressed/expanded
Work is done on a gas when it is compressed.
Work is done by a gas when it is expanded.
Define Adiabatic
Thermally isolated, no heat flow in or out of the system/process
Define: (paths)
- Isothermal (isotherm)
- Isobaric (isobar)
- Isochoric (isochar)
Isothermal - temperature is constant
Isobaric - pressure is constant
Isochoric - volume is fixed
What is heat capacity?
The energy required to change the temperature by 1 unit temperature
what is the formula for the efficiency of the Carnot cycle?
n = Work done / Heat available
What is the Carnot Theorem
- No energy operating between two reservoirs can be more efficient than the Carnot engine.
- All reversible engines have exactly the Carnot efficiency.
