I. 2 First Law Of Thermodynamics, Heat, Work, Functions Of State, Thermodynamic Potentials Flashcards
Heat
Any spontaneous flow of energy from one object to another caused by a difference in temperature between two objects.
Heat flows from . . .
Hot to Cold
Work
Any other transfer of energy into or out of a system
First Law of Thermodynamics
Energy cannot be created or destroyed—just transformed or transferred from one form to another.
ΔU = Q + W
Conduction
Transfer of heat by molecular contact
Convection
Bulk motion of a gas of liquid in which heat is carried from place to place.
Radiation
Transfer of heat by electromagnetic radiation.
Quasistatic Process
Process that occurs so slowly such that gas compressed always remains in internal equilibrium and pressure is uniform from place to place.
W = PAΔx —> W = -PΔV
Quasistatic Pressure: How about when the pressure is not constant?
W = - ∫P(V) dV
bounds are from Vf to Vi
Isothermal Compression
Slow process in which temperature of gas does not rise.
W = - NkT ∫ 1/V dV —> -NkT(ln Vf - ln Vi)
Bounds are from Vf to Vi
Vi > Vf if compressed; Vi < Vf if expands (negative work)
Isothermal Compression (Heat Flow Out) & Expansion (Heat Flow In)
Compression
Q = ΔU - W —> Δ(1/2 NfkT) - W —> 0 - W —> NkT ln(Vf/Vi)
U is proportional to T
Thus heat input is minus the work.
Compression: Q is negative
Expansion: Q is positive
Adiabatic Compression
Process so fast that no heat escapes from gas during process.
ΔU = W —> f/2 NkdT = -PdV —> f/2 dT/T =-dV/V
integrate to get: f/2 ln(Tf/Ti) = -ln (Vf/Vi) —> VT^f/2 —> V^ λP where λ = (f+2)/f
Equipartition Theorem
Internal energy of system divides itself equally amongst all degrees of freedom.
At temp T, the average energy of any quadratic degree of freedom is 1/2 kT.
U = Nf 1/2 kT
