This results in the ability to see distant objects clearly with vision becoming blurry for close objects. Hyperopia, or farsightedness, is a common vision problem that occurs as a result of these light rays entering the eyeball but converging behind the cornea. Image formation in the human eyeball occurs when parallel light rays refract through the eye lens and converge on the retina. When 1 mole of sodium metal reacts with 1 mole of chlorine gas to form solid sodium chloride, what is the heat of formation? Some lattice energies are given in the table. If the charge is constant, increasing size lowers the lattice energy. If the size is constant, increasing charge increases the lattice energy. Lattice energies depend on the charge and on the size of the ions in the array. The higher the lattice energy, the stronger the attractions and the higher melting the solid. The lattice energy of an ionic compound is a measure of the attractive forces between the ions. In solid sodium chloride, each positive ion is surrounded by 6 negative ions, and each negative ion is surrounded by 6 positive ions in a cubic lattice array. Most of the energy that is given off is due to the formation of solid sodium chloride from the gaseous ions. The chloride ion reacts with the sodium ion.Ĭl – (g ) + Na + (g ) → NaCl (s) ΔH o rxn = −771 kJĪddition of the five elementary equations gives the sum equation for the formation of solid sodium chloride. This quantity is the electron affinity of chlorine.ĥ. This quantity is the first ionization energy of sodium vapor.Ĭl (g ) + e – → Cl – (g ) ΔH o rxn = −349 kJ Na (g ) → Na + (g ) + e – ΔH o rxn = 496 kJ \frac Cl2 (g ) → Cl (g ) ΔH o rxn = 121 kJ The reaction takes place in five elementary steps: The energy that is released is the enthalpy of formation of solid sodium chloride, which is also called the heat of formation. The reaction between sodium metal and chlorine gas is spontaneous and releases energy.
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