Thermo Flashcards
Isolated systems?
Don’t allow transfer of mass or energy in or out
e.g. thermos flask
Closed systems?
Allow transfer of energy in or out but mass remains constant
e.g. gas in a cylinder
Open systems?
Mass and energy can be transferred in or out
e.g. centrifugal compressor
Intensive properties?
Properties which are independent of mass/system size
Examples of intensive properties
Temp, density, pressure, specific enthalpy
Extensive properties?
Properties which are dependent/proportional to mass or system size
Can be converted to intensive by dividing one property by another e.g mass/vol = density
total energy/mass = specific energy
Examples of extensive properties
Volume, internal energy, enthalpy
State variables?
Describe state of the matter @ equilibrium
Independent of the path to reach them
Examples of state variables
Temp, pressure, vol, entropy, mass
Isothermal process?
System changes without temp changing
Remains in thermal equilibrium
e.g. refrigerator
Isobaric process?
System changes without pressure changing
e.g. boiling water to steam
Isocharic process?
System changes without volume changing
e.g. ideal Otto cycle / a pressure cooker
Adiabatic process?
System changes without any heat or energy transfer occuring
e.g. piston in car engine
Process functions?
Describe the route to move away from equilibrium, depend on path
Give finite amounts, rather than a change, when integrated
e.g. work, heat
Zeroth law of thermo?
When two objects are separately in thermal equilibrium with a third, they are all in thermal equilibrium
Examples of sources of potential energy within a system
-Attractive and repulsive forces
-Sub-molecular energy associated with nuclei and electrons e.g. bonds
First law of thermo?
Energy can’t be created or destroyed
How are irreversible and reversible processes shown on a PV plot?
-Irreversible are shown as a dashed line, as the intermediate steps between the initial and final states are not in equilibrium
-Reversible are a solid line as the system passes through a set of equilibrated states, but is generally a slow process
What are irreversible processes?
Those which can’t return to a previously equilibrated state by simply reverting back to the original conditions
What are reversible processes?
Those where you can move from one equilibrated stater to another (quasi-statically) by simply altering the conditions of the system
What is the entropy change of any system and its surroundings, when considered together?
-Gives a positive value
-Approaches zero when the process approaches reversibility
What is the 2nd law of thermo?
For an irreversible process the combined entropy of the system and environment will increase
What are the 4 steps of a carnot cycle/engine
1) Isothermal process
2) Adiabatic process
3) Reverse isothermal process
4) Reverse adiabatic process
What is a carnot engine
-A reversible engine, dS = 0`
-Able to create work
-If run backwards, it requires work (refrigeration)
