Question

Use the References to access important values if needed for this question. Calculate the lattice energy of CuBr(s) using the following thermodynamic data (all data is in kJ/mol). Note that the data given has been perturbed, so looking up the answer is probably not a good idea. Cu(s) AHsublimation 318 kJ/mol Cu(g) Ionization energy = 725 kJ/mol Br-Br(g) Bond energy 173 kJ/mol Br(g) Electron affinity -345 kJ/mol CuBr(s) AHof -125 kJ/mol kJ/mol Do you expect this value to be larger or smaller than the lattice energy of Cul(s)? req req larger smaller er Retry Entire Group 4 more group attempts remaining 2req Trea

Answer 1

Lattice energy for CuBr

dHf = dHsub[Cu] + dH[IE Cu] + dH[BE Br2] + dH[EA Br] + lattice energy

feeding values from above,

-125 = 318 + 725 + 173 - 345 + lattice energy

lattice energy of CuBr = -996 kJ/mol

For CuI, we expect the lattice energy to be lower than CuBr as the electronegativity difference between Cu and Br is lower. Less attraction between the two ions gives lower lattice energy.