Calculate the lattice energy for CaF 2. The sublimation energy for Sr is 164 kJ/mol, E i1 = +549.5 kJ/mol, E i2 = +1064.2 kJ/mol, E ea for Cl (g) = -348.6 kJ/mol, energy for the formation of one mole of SrCl 2 from its elements = -803.7 kJ/mol, and the bond dissociation energy for Cl 2 (g) = +243 kJ/mol.Įxercise 5. Which has the highest lattice energy, Na 3P or Na 2S?Įxercise 4. Order the following ionic compounds from lowest to highest lattice energy. Are the values you found reasonable compared to the lattice energy of NaCl (787.1 kJ/mole) determined in class Explain why or why not. How do the three values compare MgO crystallizes in the rock salt structure, the same as NaCl. What is the lattice energy for MgF 2?Įxercise 2. Calculate the theoretical lattice energy of MgO using both theoretical equations and using a Born-Haber cycle. Consider the following Born-Haber cycle for MgF 2. Worksheet: Ionic Compounds, Born-Haber Cycle, and Lattice EnergyĮxercise 1. A more extensive list can be found in other tables or in the Handbook of Physics and Chemistry. The lattice energy of NaCl, for example, is 787. The lattice energies of ionic compounds are relatively large. In the case of NaCl and MgCl 2, the MgCl 2 has the larger lattice energy because the magnesium cation is smaller, and the charge is a +2 rather than a +1 for the sodium ion.īelow is a table with the lattice energies of some ionic compounds. Na + ( g) + Cl - ( g) NaCl ( s) Ho -787.3 kJ/mol. This is because the charges are the same, but the potassium ion is larger than the sodium ion. For example, the lattice energy of NaCl is larger than the lattice energy of KCl. Lattice energies are large when ions are closer together, the distance between the ions is small and when the charges are larger. Coulomb’s law is equal to a constant, k, multiplied by the product of the ion charges, z 1 and z 22, between the ions. Recall, lattice energy is positive meaning it is endothermic. Na + ( g) + Cl - ( g) NaCl ( s) Ho -787.3 kJ/mol. Rank the lattice energy (ionic bond strength) for the following formulas, 1 being strongest: LiF NaF NaCl NaI KI Strategy: When Charges are Equal, Use Ion. The Madelung constant for a three-dimensional lattice is calculated by starting from an ion placed at the lattice’s centre and then moving radially until the first neighbours, having charges of opposite value, at. The stronger the bond, the higher the lattice energy. In a simple solid, like the NaCl in the figure, the Madelung constant depends on the crystal type and by inter-ionic distances. Lattice energy, E lattice is dependent on the strength of the bond between the cation and anion in an ionic bond. The lattice energy is always positive, because it takes energy to separate the ions from the solid. Let us understand how to use Born-Haber cycle to determine the lattice energy of sodium chloride (NaCl) 1 4. It utilizes the known thermodynamic quantities like ionization energy and electron affinity. The equation for the lattice energy is the reverse of the equation in Step 5 in the figure below, for the formation of the solid from its ions which releases 787 kJ/mol of energy.Ī Born-Haber cycle allows the calculation of the lattice energy for a solid ionic compound. The Born-Haber cycle takes advantage of the enthalpy change to determine the lattice energy of ionic compounds indirectly. The process absorbs energy, and is highly endothermic. In many applications, all but one leg of the cycle is known, and the job is to determine the magnitude of the missing leg.Lattice energy, E lattice is the energy required to separate one mole of a solid ionic compound into its gaseous ions. Example 1: Compute the Lattice energy of NaCl by using Born-Lande equation. Figure 4.1.5 An 'exploded' view of the unit cell for an NaCl crystal lattice. To calculate the energy change in the formation of a mole of NaCl pairs, we need to multiply the energy per ion pair by Avogadro’s number: ( Eleft ( -9.79 times 10. Figure 3.6.1: the Born-Haber Cycle for NaCl. U L equilibrium value of the lattice energy. If it requires energy, the energy change is positive, energy has to be given to the atoms. An example of the Born-Haber Cycle for NaCl is shown below. This can be depicted graphically, the advantage being that arrows can be used to indicate endothermic or exothermic changes.
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