Enthalpy change of vaporization

Fig. 5.3 The enthalpy change of adsorption of chlorides on fused silica (in the presence of chlorinating agents) versus enthalpy change of vaporization of the compounds.

The enthalpy change of vaporization was calculated using the approximation... 

EXAMPLE 11.9 Find the enthalpy change of vaporization of ethanol from the graph in Fig, 11,2. 

EXAMPLE 11.10 Calculate the slope m and the intercept b for the least-squares line for the data in Table 11.3, using ln(F) as the dependent variable and /T as the independent variable. Calculate the enthalpy change of vaporization from the slope. 

EXAMPLE 11.13 Assume instead of the given expected errors that the expected error in the logarithm of each vapor pressure in Table i 1.3 is equal to 0.040. Find the expected error in the least-squares slope and in the enthalpy change of vaporization. 

EXAMPLE 11.14 Calculate the residuals for the linear least-squares fit of Example 11.10. Find their standard deviation and the probable error in the slope and in the enthalpy change of vaporization, using the standard deviation of the residuals. 

These figures differ slightly from those of Example 11.9, and since the expected errors in the logarithms are not all equal to each other, these values are likely more nearly correct. The slope gives a value of the enthalpy change of vaporization... 

The following is a set of student data on the vapor pressure of liquid ammonia, obtained in a physical chemistry laboratory course. Find the indicated enthalpy change of vaporization. Remember that the Kelvin temperature must be used. 

When dissolving a gas in the liquid phase the enthalpy of the gas changes similarly to the enthalpy change of vaporization. The enthalpy of solution at infinite dilution - the enthalpy difference between the gaseous and the dissolved solute - can be expressed with the help of the Henry constant as derived below. 

Because AyapTf is an enthalpy change per amount of vaporization, it would be more accurate to caU it the molar enthalpy change of vaporization. ... 

Z atomic number Avapfy enthalpy change of vaporization... 

The enthalpy of atomization is an indication of the strength of bonding in a substance. For a solid to break up into atoms, it may first melt (accompanied by the standard enthalpy change of fusion), then evaporate (accompanied by the standard enthalpy change of vaporization) and finally, in the gas phase, any remaining bonds break to give individual atoms. 

The standard enthalpy change of vaporization is the enthalpy change which occurs (at constant pressure) when one mole of a pure liquid is completely vaporized under standard conditions. The standard enthalpy change of fusion is the enthalpy change which occurs (at constant pressure) when one mole of a pure solid is completely melted under standard conditions. 

Exercise 16.4. The following data give the vapor pressure of water at various temperatures. Transform the data, using In (P) for the dependent variable and 1/T for the independent variable. Carry out the linear least-squares fit by hand, calculating the four sums. Find the molar enthalpy change of vaporization. 

Example 16.12. Fit the data in Table 16.1 to a fourth-degree polynomial. Obtain a formula for the derivative dP/dr. Evaluate the derivative for 45 C and use this value to calculate the molar enthalpy change of vaporization. 

---