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Thermal Physics > george notes > Flashcards

george notes Flashcards

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1
Q

Ideal gas equation

A

PV=1/3NM =2/3 N(1/2m

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2
Q

ideal gas heat capacity relation

A

Cp=Cv+R

gamme = Cp/Cv

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3
Q

ideal gas relation to U

A

PV=2/3 U

PV = U(gamma-1)

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4
Q

monotomic ideal gas heat capacity

A

C_v = 3/2 R Cp+5/2 R
hence
gamm = 5/3

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5
Q

diatomic ideal gas heat capacity

A

Cv=7/2R Cp=9/2 R

gamma =9/7

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6
Q

four steps to the Carnot cycle

A

isothermal expansion
adiabatic expansion
isothermal compression
adiabatic compression

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7
Q

engine efficiency equation

A

e=WQ=Q1-Q2/Q1 = 1-Q2/Q1

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8
Q

alternative form of the engine efficiency equation for the carnot engine

A

e=1-T2/T1

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9
Q

entropy equation

A

S=Q/T

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10
Q

entropy of adiabatic expansion

A

entropy of adiabatic expansion is constant

S(V,T) = NKb[lnV+1/(gamma-1) lnT] +a

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11
Q

first and second law of thermodynamics written together

A

du=dq+dw

du = Tds+ (-)PdV

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12
Q

how many thermodynamic processes does a system with 2 degrees of freedom have and what are they

A

4 thermodynamic processes

du = Tds - PdV
dH =TdS + VdP Enthalpy
dF = -SdT - PdV Helmholtz free energy
dG = -SdT + VdP gibbs

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13
Q

what does enthalpy represent

A

the heat transfer at constant temperature

H=H(P,V) = U + PV

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14
Q

what does Helmholtz and Gibbs free energy describe

A

they describe processes at constant temperature

F=F(T,V) =U -TS

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15
Q

what is the decrease in the Helmholtz energy

A

It is the maximum amount of work that may be extracted from a system during an isothermal change

Delta F = Delat U - T(Delta) S

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16
Q

reactions go in which way to favour the Gibbs?

A

Reactions go to minimise the Gibbs, it is constant for a reversible process at constant Temperature and pressure

17
Q

what is the gibbs used to determine

A

the equilibrium states for a system with several phases

18
Q

coefficient of performance for a backwards engine

A

Tc/Th-Tc = heat out / workdone

approx. 10 for a backwards carnot engine e.g. fridge

19
Q

coefficient of performance of a heat pump

A

COP = |Qc|/W = Qc/Qh-Qc

20
Q

coefficient of performance for a carnot heat pump

A

COP = Tc/Th-Tc

21
Q

Boyles law curve at different temperatures

A

at high temperatures isotherms approx. to boyles law curve. at lower temperatues the boyles law curve becomes distoreted.

22
Q

liquids compressible?

A

liquids are pretty incompressible

23
Q

what equation is a good approximation for O2 and N2

A

the ideal gas equation is good approximations for O2 and N2 because roomt T»Tc for these solutions

24
Q

The Clausius -clapyron equation

A

dp/dT=1Delta(S)/Delta(V) = L/T(Delta)V
where L is latent heat (absorbed)
Delta S is the change in entropy from phase 1 to phase 2

25
Q

equation for three phases to co exist

A

g1=g2=g3

26
Q

liquid to vapour transient equation

A

dp/dT = L/ Tb(Vg-Vl)

where Tb is boiling temp
Vg is gas volume
Vl is liquid volume

27
Q

how many constraints does the triple point have

A

it has three constraints often the entropy increases when changing phase with increasing T

28
Q

why do liquids cool as they evaporate

A

they lose the more enegetic molecules

29
Q

what is intermolecular potential energy characterised by

A

the equilibrium separation ro and depth of the well e

30
Q

Van der Waals forces equation

A

(P+a/Vm^2)(Vm-b)=RT

31
Q

what do a stand for in the van de waals equation

A

The parameter a allows for the long-range intermolecular attraction which serves to lower the observed pressure

32
Q

what does b stand for in the van der waals equation

A

the parameter b can be viewed as an excluded volume in a gas due to the present of the molecules (i.e. due to hard core repulsion)

33
Q

what are intermolecular forces proportional too

A

the number of neighbours and collision frequency so f^2

34
Q

when does the van der waals equation break down

A

for temperatures below the critical temperature. it is only good for small constraints

35
Q

the entropy change during melting

A

Delta S f= mLf/Tf

36
Q

Nernest-simon formulation of the third law

A

if Delta S is the entropy change during any reversible isothermal process ina condensed system then Delta S tends to zero as the temperature goes to absolute zero

37
Q

what is the order of phase transition

A

the order of phase transition is defined as the order of the lwest differential of the Gibbs function which shows a discontinuity at the transion

Thermal Physics (2 decks)

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