formulario termodinamica

Pure Substances 3b-1 PROPERTIES OF

A substance with fixed chemical composition is a pure substance (examples: water is a pure substance; air is not a pure substance but a mixture)Ideal gas - Equation of state

- Energy and enthalpy of Ideal GasesReal gas - P-V diagrams

- Phase transitions

- Equation of stateSpecific heats (Cv & Cp) [CB 2-all]

Pure Substances 3b-2 IDEAL GAS

Can be imagined as large ensemble of molecules interacting with each other only though relatively short collisionsEquation of state PV = NRT where P is pressure, V is total volume, T is the absolute temperature (K), N - number of moles,

R=8.314 kJ/(kmol⋅K) is the universal gas constantOther forms -per mole: Pv = RT

Nper mass: Pv = RTmEnergy and enthalpy

In ideal gases: u=u(T) and h=h(T) do not depend on P In other pure substances u=u(T,P) and h=h(T,P)

Pure Substances 3b-3

REAL GASstate is characterized by 2 parameters for example: T&P, P&v, T&v or T&r that is u=u(T,P), h=h(T,P), v=v(T,P)

-Equation of state: Pv = ZRT;

Z=Z(PR,TR) is compressibility factor TR=T/Tcr, PR=P/Pcr are reduced temperature & pressure

Tcr, Pcr are critical temperature & pressure2-parameter diagrams are to be used P:v, T:v or P:T

Pure Substances 3b-4 PHASE CHANGESsolid l iquid gas(vapor) plasma solid --> gas sublimationSaturation - equilibrium between liquid and vapor P=Psat(T)Critical point (with Tcr,Pcr) point where saturated liquid is no different from saturated vaporTriple point - the only point for each substance where liquid, gas and solid phases can coexist in equilibrium mvaporQuality of liquid/vapor mixture = mvapor+mliquid

Pure Substances 3b-5 HEAT CAPACITIES linking changes of temperature T to heat Q1st Law: dU = dQ - PdV; dH = dQ + VdPconstant volume dU = dQ

- -In ideal gases cp - cv = RFor incompressible substances Cp = CvIdeal gas with constant heat capacities: DU=CvDT; DH=CpDT