What is the lattice energy of NaBr?
heat of formation of NaBr = -362 kJ/mol
heat of sublimation for Na = 107.30 kJ/mol
ionization energy for Na = 496 kJ/mol
bond dissociation energy for Br2 = 190 kJ/mol
electron affinity of Br = -325 kJ/mol
heat of vaporization for Br2 = 30.90 kJ/mol
Heat formation = Hsubl + IP + 1/2(bond diss) + electron affinity(a negative value) + 1/2(vaporization) + Ecrystal lattice.
Substitute and solve for E crystal.
If your text defines crystal lattice energy as -Ecrystal, then reverse the sign.
Something like +750 or so kJ/mol.
To calculate the lattice energy of NaBr, we can use the Born-Haber cycle approach. The lattice energy is the energy change that occurs when one mole of an ionic compound is formed from its constituent ions in the gas phase.
Here are the steps to calculate the lattice energy:
Step 1: Write the balanced reaction for the formation of NaBr.
2 Na (g) + Br2 (g) → 2 NaBr (s)
Step 2: Calculate the enthalpy change for each step of the Born-Haber cycle.
a) Sublimation of sodium:
Na(s) → Na (g)
Enthalpy change = heat of sublimation of Na = 107.30 kJ/mol
b) Dissociation of bromine:
Br2 (l) → Br2 (g)
Enthalpy change = heat of vaporization of Br2 = 30.90 kJ/mol
c) Ionization of sodium:
Na(g) → Na+ (g) + e-
Enthalpy change = ionization energy of Na = 496 kJ/mol
d) Electron affinity of bromine:
Br(g) + e- → Br- (g)
Enthalpy change = electron affinity of Br = -325 kJ/mol
e) Formation of sodium bromide:
Na+ (g) + Br- (g) → NaBr (s)
Enthalpy change = heat of formation of NaBr = -362 kJ/mol
Step 3: Sum up the enthalpy changes for each step in the Born-Haber cycle.
ΔH = (107.30 kJ/mol) + (30.90 kJ/mol) + (496 kJ/mol) + (-325 kJ/mol) + (-362 kJ/mol)
Step 4: Calculate the lattice energy.
The lattice energy can be calculated as the negative of the enthalpy change in the step e).
Lattice energy = -ΔH = -(107.30 kJ/mol + 30.90 kJ/mol + 496 kJ/mol - 325 kJ/mol - 362 kJ/mol)
Therefore, the lattice energy of NaBr is approximately equal to -285 kJ/mol.
To calculate the lattice energy of NaBr, we can use the Born-Haber cycle, which is a method that involves a series of steps to determine the lattice energy of an ionic compound.
The Born-Haber cycle takes into account the various energy changes associated with the formation of an ionic compound from its constituent elements. These energy changes are:
1. The heat of formation of NaBr (-362 kJ/mol): This is the energy change when one mole of NaBr is formed from its elements in their standard states.
2. The heat of sublimation for Na (107.30 kJ/mol): This is the energy required to convert one mole of solid Na into gaseous Na atoms.
3. The ionization energy for Na (496 kJ/mol): This is the energy required to remove one electron from a mole of gaseous Na atoms to form Na+ ions.
4. The bond dissociation energy for Br2 (190 kJ/mol): This is the energy required to break one mole of Br-Br bonds in gaseous Br2.
5. The electron affinity of Br (-325 kJ/mol): This is the energy change when one mole of gaseous Br atoms accepts an electron to form Br- ions.
6. The heat of vaporization for Br2 (30.90 kJ/mol): This is the energy required to convert one mole of liquid Br into gaseous Br2.
The lattice energy of NaBr can be calculated using the following equation:
Lattice Energy = Heat of Formation - Heat of Sublimation (Na) - Ionization Energy (Na) + Bond Dissociation Energy (Br2) - Electron Affinity (Br) - Heat of Vaporization (Br2)
Plugging in the values given:
Lattice Energy = -362 kJ/mol - 107.30 kJ/mol - 496 kJ/mol + 190 kJ/mol - (-325 kJ/mol) - 30.90 kJ/mol
Lattice Energy = -362 kJ/mol - 107.30 kJ/mol - 496 kJ/mol + 190 kJ/mol + 325 kJ/mol - 30.90 kJ/mol
Lattice Energy = -480.20 kJ/mol
Therefore, the lattice energy of NaBr is approximately -480.20 kJ/mol.