Boiling point of the metals

Zinc is produced by reduction of 2inc oxide, usually a calcine obtained by roasting 2inc sulfide concentrates. Carbon is used in the absence of air at 1200—1300°C, well above the boiling point of the metal (906°C). 

G. Bartha gave the boiling point of the metal chloride in the cathode light as 1005° for lithium chloride 8503 for sodium chloride 800° for potassium chloride 790° for rubidium chloride and 750° for caesium chloride. 

The mutual solubilities of Li-LiCl and Li-LiCl-KCl systems have been determined both in liquid-liquid and solid-liquid equilibrium regions. For Li-LiCl, the consolute temperature could not be detected despite raising the temperature to 1623 K. This is higher than the boiling point of the metal. Solubilities increase from 0.007 (567 K) to 0.23 (923 K) mol% LiCl in Li, and from 0.66 (935 K) to... 

Studies of the spectra of Group I metal vapors at about the boiling points of the metals show the presence of 1 % of diatomic molecules whose dissociation energies decrease with increasing atomic number (Table 6.1). These molecules provide the most unambiguous cases of covalent bonding of the alkalis some s-p hybridization is considered to be involved. 

The boiling-point of the metal under atmospheric pressure is 1300° it is 290° in the vacuum of cathode light Krafft, Bergfeld). The colour of the fume of antimony is green lAncK). 

Finally, for C-J temperatures above the boiling point of the metal, consideration should be given to the possible existence of distinct species in the gas phase. To include them as components in the assumed set of detonation gases requires knowledge of their molecular geometry and ideal-gas thermodynamic properties (e.g., heat capacity as a function of temperature and heat and entropy of formation). In the absence of such data, it is possible to predict the molecular geometry and thermodynamic properties via quantum-chemical and statistical-thermodynamic calculations, respectively, or to estimate them by analogy with known related molecules. 

For most of the reactions, 1 mole of gas is consumed to make a solid product, resulting in a decrease in entropy and a positive slope. The slope changes at temperatures above the boiling point of the metal. The line for the oxidation of C to CO has a negative slope because 1 mole of gas is reacting to create 2 moles of product, which involves an increase in entropy. Similarly, the line for oxidation of C to CO2 is horizontal. 

Although zinc oxide is comparatively easily reduced to free metal, it was obtained in a metal state much later than copper, iron, tin, and lead. The explanation is that reduction of zinc oxide with coal requires high temperature (about H00°C). The boiling point of the metal is 906°C therefore, highly volatile zinc vapour escapes from the reaction zone. 

The forces of attraction between molecules are known as intermolecular forces. Intermolecular forces vary in strength but are generally weaker than bonds that join atoms in molecules, ions in ionic compounds, or metal atoms in solid metals. Compare the boiling points of the metals and ionic compounds in Figure 5.8 (on the next page) with those of the molecular substances listed. Note that the values for ionic compounds and metals are much higher than those for molecular substances. 

---