Thermal Physics Flashcards
(26 cards)
What is heat?
This is the form of energy transferred between substances due to temperature differences between them
What is temperature?
Temperature is the property which determines whether or not a system is in thermal equilibrium with other systems
What is a system?
A system is defined to be a portion of the universe with measurable pressure or volume which determines the equilibrium state of the system
What is the difference between a closed and isolated system?
An isolated system is one that does not interact with its surroundings. A closed system is one in which energy but not material can be exchanged.
What is an adiabatic wall?
A system which is thermally isolated and only mechanical energy can be exchanged with the surroundings. E.g a vacuum flask
What is a dia thermal wall
Where heat exchange is permitted . Systems connected by a diathermal wall are in thermal contact. E.g a metal wall
What is it meant by thermal equilibrium?
If two systems are put in thermal contact, generally changes occur in both. After some time, no further changes occur and the two systems are said to be in thermal equilibrium.
What is the first law of thermodynamics?
Energy cannot be created or destroyed, only transferred or converted from one form to another. (Delta U = Q-W)
What is an equation of state?
A mathematical relationship between the state variables of a system that describes the state of matter under a set of physical conditions. E.g PV = nRT
What is the difference between macroscopic and microscopic variables ?
Macroscopic : large scale or bulk properties of a gas (P, V, T)
Microscopic : properties on the atomic level (v_(rms) , v_(mp))
What is it meant by thermodynamic degrees of freedom?
The number of independent variables (P, T, V) that can be changed without affecting the others while still defining the state of a thermodynamic system in equilibrium.
What is the equipartition of energy theorem?
A classical system in thermal equilibrium at temperature T has a mean energy of 1/2k_bT per translational degree of freedom
What is Dalton’s law of Partial pressures ?
The total pressure exerted by a mixture of gases is equal to the sun of the pressures exerted by those gases separately, and each gas contributes a partial pressure.
P_j = (n_j RT)/V
Distinguish between reversible and irreversible processes
Irreversible processes are those in which energy is dissipated. (Delta S >0)
Reversible processes are the opposite (Delta S = 0)
What is it meant by entropy?
Entropy (S) is a macroscopic variable that quantifies the degree of disorder in a system.
State the second law of thermodynamics.
In an adiabatically isolated system , change in entropy Is greater than or equal to 0
What is a heat engine?
A heat engine is a devise that converts heat into mechanical energy in a cyclic process.
What is a cyclic process?
A process that returns a system to its initial state at the end of a process
What is a heat pump and refrigerator?
Heat pump: takes heat from out with a house and pumps it inside
Refrigerator: pumps heat from a cooled area into the space outside it.
What is the Carnot cycle ?
It is an idealised thermodynamic cycle that represents the most efficient possible heat engine
What is Carnot’s Theorem?
No engine operating between two temperature reservoirs can be more efficient than a Carnot engine operating between the same two temperatures.
What is it meant by isovolumetric, isothermal and isobaric
Isovolumetric - Volume remains constant
Isothermal - Temperature remains constant
Isobaric - Pressure remains constant.
How can two gases have the same speed distribution
The area under the distribution curve doesn’t change with temperature
Describe what happens to entropy when ice melts
Entropy increases because the molecules become more disordered during the phase chnage from solid to liquid
