Thermal Physics Flashcards
What are the three laws of thermodynamics?
Zeroth law, Frist law, Second law
What is Zeroth law?
If A and B are in thermal equilibrium with C then A and B are in thermal equilibrium with each other
What is First law?
ΔE=Q-W (ΔE is net change in total energy, Q is heat added to the system, W is work doen by the system)
What is Second law?
In all spontaneous processes, the entropy of the universe increases i.e. entropy always increases with time
What is entropy?
The degree of disorder or randomness in a system
What is a system?
A portion of the Universe with certain measurable
quantities (such as pressure or volume) which determine the equilibrium state of
the system
What is an isolated system?
A system that does not interact with its surroundings by exchanging heat
energy, mechanical energy or material
What is a closed system?
A system in which energy but not material can be exchanged
What is am adiabatic wall?
The system is thermally isolated and
only mechanical energy (not heat) can be exchanged with the surroundings (e.g. a vacuum flask)
What is a diathermal wall?
Heat exchange is permitted; systems
connected by a diathermal wall are in thermal contact (e.g. a metal wall)
What does equilibrium mean?
All bulk physical properties are uniform throughout the system, they are time-independent
What does macroscopic mean?
Large-scale or bulk properties of a gas (e.g.: P, V, T)
What does microscopic mean?
Properties on the atomic-level (e.g.: vrms, vmp.)
What are state variables?
These define the state of a system
What does intensive mean?
Independent of the size of the system
Give 2 examples of intensive properties
pressure, tension
What does extensive mean?
Proportional to the size of the system
Give 2 examples of extensive properties
volume or length
What are equilibrium states of thermodynamic systems determined by?
Suitable pairs of conjugate variables
What is a pair of conjugate variables?
One variable will be intensive and the other extensive
Give an example of pairs of conjugate variables for a gas and for a stretched wire
(P, V) for a gas. Or
(tension, length) for a stretched wire
What dimensions does the product of all conjugate pairs have?
The dimentions of energy
What is a function of state?
Any quantity which takes a unique value for each equilibrium state of a system
Give an example of a state funtion
Internal energy U or entropy S
What do functions of state depend on?
Only on the state itself and not on how that state was
produced
Why is heat not a function of state?
Because it is associated with a transfer of energy between states
What is heat (Q)?
The form of energy transferred between substances due to temperature differences between them
What happens in terms of heat when two objects are NOT in thermal equilibrium?
Heat flows from the hotter object to the colder object until thermal equilibrium is reached
What is temperature?
The property which determines whether or not a system is in thermal equilibrium with other systems
What are is the condition for Thermal equilibrium?
same temperature
What is the condition for Mechanical equilibrium?
no unbalanced forces acting
What is the condition for Chemical equilibrium?
no chemical reactions occurring
What do Non-uniformities in a system result in?
a gradient and, hence, momentum, heat
and / or matter flows until thermodynamic equilibrium is reached
What are Consequences of Thermodynamic Equilibrium On a macroscopic level?
variables have constant values in time and space (i.e.:
throughout the system)
What are Consequences of Thermodynamic Equilibrium On a microscopic level?
any process (e.g.: diffusion, collisions) must have an equal probability of going in the opposite direction
What is the equation of state?
f(P, V, T) = 0
What is an ideal gas?
A gas for which hydrostatic equilibrium holds. i.e.: the inward force of gravity balances the outward gas pressure
What do we assume in an ideal gas?
that atoms or molecules are non-interacting and
point-like
What is the equation of state with R = 8.31 J K^–1 mol^–1?
f(P, V, T) = PV – nRT = 0
How would we write the equation of state with the boltzmann constant?
PV – nkBT = 0
What is a non-ideal gas?
A gas which has molecules with a finite volume and as a consequence, intermolecular forces (which are attractive) must be considered
What is The equation of state for a van der Waals gas?
f(P, V, T) = (P+(n^2a/V^2))(V-nB)-nRT=0
What is An indicator diagram?
a graph of an intensive variable (e.g.: P) against its conjugate extensive variable (e.g.: V)
What is an isotherm?
The continuous line between any two states (P, V) and (P’,V’) in thermal equilibrium with each other (they will beat the same temperature)
Describe Isotherms for a van der Waals gas (3)
1. The isotherms look the same for both gas types at high temperatures 2. The behaviour begins to change as temperatures drop 3. Below a critical temperature Tc a phase change occurs
