The others are progressively more insoluble in water (K sp is 10 -10, 10 -13, and 10 -16 for AgCl, AgBr, and AgI), reflecting increasing covalency as Δχ decreases.Trending Questions How picric acid is strong acid? What is the difference between a short-chain and a long-chain hydrocarbon? What chemical form is sodium mined? What is the name for n4O? What is the relationship between the atomic mass of an element and a mole of that elements atoms? What colors mix to make a lilac color? How do you remove polyvinyl alcohol applied as stiffener in the fabric? Is C5H5N a strong acid or weak acid? What is carbonated water solute and solvent? Why must the oxygen cylinder valve be opened all the way to the top? How much sodium chloride can be dissolved in 20 degree Celsius water into 2 L of water? Why is the oxidation number of Br in BrO3 5? What is the percentage of chromium in 5. Science Chemistry 8.83 Construct a Born-Haber cycle for the formation of the hy- pothetical compound NaCl2, where the sodium ion has a 2+ charge (the second ionization energy for sodium is given in Table 7.2). Of these compounds, only AgF is soluble in water and should be thought of as an ionic compound. Our lattice energy calculation overestimates the ionic contribution in the case of the heavier silver halides, but underestimates the covalent contribution. It requires 769 kJ of energy to dissociate one mole of solid NaCl into separate gaseous Na + and Cl ions: NaCl(s) Na+(g) +Cl(g) H 769kJ (6.1.1) (6.1.1) NaCl ( s) Na + ( g) + Cl ( g) H 769 k J. The covalent bonding contribution to the lattice energies of AgCl, AgBr, and AgI makes these salts sparingly soluble in water.Īgain, we can interpret the fortuitous agreement between the calculated and experimentally obtained energies in terms of compensating errors. The strong electrostatic attraction between Na + and Cl ions holds them tightly together in solid NaCl. This reaction is used as a qualitative test for the presence of halide ions in solutions. Should we interpret the good agreement with values calculated from the ionic model to mean that these compounds are ionic? Clearly, this description is inappropriate for AgI, where the electronegativity difference Δχ is only 0.6 (compare this value to 0.4 for a C-H bond, which we typically view as non-polar).Ī drop of siver nitrate solution, when added to a dilute hydrochloric acid solution, results in the immediate formation of a white silver chloride precipitate. However we are still obtaining answers within about 12% error even for AgI. Looking at the table, we see that the error is small for AgF and becomes progressively larger for the heavier silver halides. It is interesting to repeat this exercise for the silver halides, which have either the NaCl structure (AgF, AgCl, AgBr) or zincblende structure (AgI). The errors in this case are only about 1% of E L. For example sodium chloride, NaCl, which is nothing but Na + and Cl. The table below shows results of more detailed lattice energy calculations for ionic fluorides in which the van der Waals term is explicitly included. anion anode cathode cation electron lattice energy negatively (-) charged. We can do better by explicitly including the short-range van der Waals attractive energy between ions. The two errors partially compensate, so the overall error in the calculation is small. Question: Which of the following compounds has the largest lattice energy NaCl CaCl2 RbCl MgCl2. If we underestimate the attractive energy of the crystal lattice, the energy minimization criterion ensures that the repulsion energy is underestimated as well. This problem has been solved Youll get a detailed solution from a subject matter expert that helps you learn core concepts. This is because we used energy minimization to obtain the repulsion energy in the Born-Mayer equation. The result is promising because we neglected the van der Waals term.īut.how did we get away with neglecting the van der Waals term? Here we have to subtract 2RT to convert our cycle of energies to a cycle of enthalpies, because we are compressing two moles of gas in making NaCl(s) and PΔV = ΔnRT, where Δn = -2.Įxperimentally ΔH f for NaCl is -411 kJ/molīecause all the other numbers in the cycle are known accurately, the error in our calculation is only about 15 kJ (about 2% of E L).
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