Note the newest Trend
Unstable compounds features lower boiling items and you can apparently weak intermolecular relationships; nonvolatile compounds enjoys higher boiling hot items and you may seemingly solid intermolecular relationships.
The latest exponential boost in vapor stress having expanding temperature inside the Profile “The latest Vapor Demands of a lot Water once the a purpose of Temperatures” lets us explore pure logarithms to share the new nonlinear relationship as the a beneficial linear you to. nine “Crucial Enjoy 6”.
ln P = ? ? H vap Roentgen ( step 1 T ) + C Picture having a straight line : y = m x + b
where ln P is the natural logarithm of the vapor pressure, ?Hvap is the enthalpy of vaporization, R is the universal gas constant [8.314 J/(mol·K)], T is the temperature in kelvins, and C is the y-intercept, which is a constant for any given line. A plot of ln P versus the inverse of the absolute temperature (1/T) is a straight line with a slope of ??Hvap/R. Equation 11.1, called the Clausius–Clapeyron equation A linear relationship that expresses the nonlinear relationship between the vapor pressure of a liquid and temperature: ln P = ? ? H vap / R T + C , where P is pressure, ? H vap is the heat of vaporization, R is the universal gas constant, T is the absolute temperature, and C is a constant. The Clausius–Clapeyron equation can be used to calculate the heat of vaporization of a liquid from its measured vapor pressure at two or more temperatures. , can be used to calculate the ?Hvap of a liquid from its measured vapor pressure at two or more temperatures. The simplest way to determine ?Hvap is to measure the vapor pressure of a liquid at two temperatures and insert the values of P and T for these points into Equation 11.2, which is derived from the Clausius–Clapeyron equation:
ln ( P 2 P 1 ) = ? ? H v an excellent p R ( 1 T 2 ? 1 T 1 )
Conversely, if we know ?Hvap and the vapor pressure P1 at any temperature T1, we can use Equation 11.2 to calculate the vapor pressure P2 at any other temperature T2, as shown in Example six.
Example 6
From these data, calculate the enthalpy of vaporization (?Hvap) of mercury and predict the vapor pressure of the liquid at 160°C. (Safety note: mercury is highly toxic; when it is spilled, its vapor pressure generates hazardous hongkongcupid, kimin seni ödeymeden sevdiÄŸini nasıl görürsün? levels of mercury vapor.)
A Use Equation 11.2 to obtain ?Hvap directly from two pairs of values in the table, making sure to convert all values to the appropriate units.
A The table gives the measured vapor pressures of liquid Hg for four temperatures. Although one way to proceed would be to plot the data using Equation 11.1 and find the value of ?Hvap from the slope of the line, an alternative approach is to use Equation 11.2 to obtain ?Hvap directly from two pairs of values listed in the table, assuming no errors in our measurement. We therefore select two sets of values from the table and convert the temperatures from degrees Celsius to kelvins because the equation requires absolute temperatures. Substituting the values measured at 80.0°C (T1) and 120.0°C (T2) into Equation 11.2 gives
ln ( 0.7457 torr 0.0888 torr ) = ? ? H vap 8.314 J/(mol · K) [ 1 ( 120 + 273 ) K ? step 1 ( 80.0 + 273 ) K ] ln ( 8.398 ) = ? ? H vap 8.314 J · mol ? step 1 · K ? step 1 ( ? dos.88 ? 10 ? cuatro K ? step 1 ) dos.13 = ? ? H vap ( ? 0.346 ? ten ? cuatro ) J ? step one · mol ? H vap = 61,400 J/mol = 61 .cuatro kJ/mol