THERMOPHYSICAL PROPERTIES

 
THERMOPHYSICAL PROPERTIES:X

YOUR HONOR

STANDARD STATEXXX

Standard StateX
  • mechanical properties - related to structural uses.

    All follow-on needs of properties, eventually encounter the need of information about states of substances at temperatures other than 25C. With all "follow-on" uses...

    The idea "state of a substance" supposes variability of that state. Indeed substances behave differently (in accorsd with their inner structures) when it is not STP.

    EQUATION OF STATE: (of "X") By the above approach, investigation applied to any substance one obtains a single set of data with the input information (substance and STP) to yield output information (density and phase). This beginning point consists of numbers. Pressure as a variable is written, p. Pressure as a number is written as p* meaning any possible "numerical" value of pressure. With standard state we have: vsubstance(STP) = vinner structure(25°C,1 atm).

    EQUATION OF STATE (of X):   The STANDARD STATE is the first state (it being at STP). The equation of state is a relation for change to all the other states for all other T's and p's.

    all the other states relat The equations of state for simple substances have the classical functional form v = v(T,p). The functional relation implies continuous correspondence such that were selected values for the independent variables temperature and pressure (say T=T* and p=p*) entered (presuming we have it) into the equation of state as v = v(T*,p*), the relations functional power would produce the single precise value v*. The equation of state is the beginning idea. After it is made valid for a substance, further relations are sought such as for enthalpy as h = h(T,p).

    The bounds of dependence are. For:
    i) STP solid X temperature is the dominant independent variable
    ii) STP liquid X respond to T and in special ways to very Low p
    iii) Ideal gasses are totally responsive to T and p whatever! Physical investigation of this idea have shown it to be true for ideal gases. The functional relation is v = v(const,T,p) or v = [(R/M)T/p]. The analytic and simple nature of the ideal gas equation permits it to be used so many ideal gas properties are readily avaianleof this equation of state, being pressure and temperature, and not true.
  • SOLID AND LIQUID:   Were X at STP, one might expect the density of X to change were the pressure to increase. The expectation is valid for STP X's of gas phase. However the densities condensed phase X's are immune, unchanged by pressure. Solids disrepect all pressures, greater of lower. Very low pressures migh affect liquids. For the most part, in the range of engineering pressures

    vsolid,liquid = vsolid,liquid(T).... very much less change of v with p as with T

    Thus v(T,p) becomes degenerate for solids and liquids.

    vLiquids of imposed pressure does not might be said to be degenerate. from the standard the standard atate o
  • IDEAL GASES: of the surface for f(v,T,p) = 0. The Many thermodynamic events occur within the ambient atmosphere and therefore at constant pressure. The two indeWhile gas phase event might show vawith their pressures at the constant, prevailing pressure, one atmosphere (also called standard pressure). In these cases, temperature For the very many cases where t otstandard pre the coMany substances are condensed phases at STP. Since so very many substance events Of their independent variables, prssure and temperature, liquids and solids are much less chasubstanve The
    LEAD @ ONE ATMOSPHERE:   (M = 207)
    LEAD @ 1 atm (M = 207)
    SOLID MELT/FREEZE LIQUID BOIL/CONDENSE GAS
    T < Tmelt
    ρ = 11.3 g/cm3
    cs=0.13J/g°C    		 Tmelt=327°C
    hsf= 23J/g    		 Tmelt< T < Tnb
    ρ= 10.6g/cm3
    cf=    		 Tnb = 1749°C
    hfg=866J/g    		 T > Tnb


    Vapor Pressure
    P (Pa) 1 10 100 1 k 10 k 100 k
    T (K) 978 1088 1229 1412 1660 2027


    ρ cs,avg Tmp hsf cavg
    (liq)    		 Tnbp hfg cp,avg
    (gas)
    11.3
    (g/cm3)    		 0.16
    (J/g °C)    		 327
    (J/g°C)    		 5.4
    (J/g)    		 220 1749
    °C    		 179
    (J/g)    		 360
    (J/g°C)


     
    0.037
    B/lbmF
     

         		 11.3
    B/lbmF

     

     
    621°F

     

     

     
    •   Though virtually every substance of value has been studied, suppose we encountered substance (which has not been studied) in a magical box, marked "Pure X at STP." Next visually, (X being easy) we agree upon the simple phase of X (which would be solid, liquid or gas). About acquainted with X, but for the simplest extension of understanding, we determine its density (by an appropriate textbook procedure). Thus an information set results: : the jury has reached its decision!PURE Substance "X" when put to 25°C and 1 atm, chose (of its own accord) phase* and density* : The above quick investigation of X established the very barest, minimum information, that to constitutes a "Standard State" scientific understanding of . Other would do more measurements but these are enough for here. What happened physically was that pure "" was subjected to STP, whereupon, in response, "" selected for itself a phase (which was observed) and a density (which was measured and recorded). After a bare minimum specification of is established, the various disciplines pursue the substance further to learn properties of their special interests (generally still at STP). Material and/or electrical properties of must be know for its use in structural or electrical applications . The "inner nature" of X - its chemical properties are needed to predict