Borne Haber Cycle/ Lattice Enthelpy for KBr

[dav1d]

Homework Statement

Draw the Borne Haber cycle for KBr

Homework Equations

The Attempt at a Solution

so the energy required to make the K into gas is +89kJ/mol
and it takes +420kJ/mol to take 1 electron from K

it takes +112kJ/mol to make Br a gas
it takes -342kJ/mol to give the Br an electron

and i was given -392 delta H subscrpit F superscript theta = -392kJ/mol (what does this mean?)

how do i calculate the lattice enthalpy?

Using Hess's law it should be the sum
So is it
89+420+112-342-392?

 

[nate808]

Dear student,

Thank you for your post. The Borne Haber cycle is a useful tool in understanding the formation of ionic compounds. To draw the Borne Haber cycle for KBr, we first need to understand the different steps involved in the formation of KBr.

Step 1: Formation of gaseous K (K(g))
The first step in the Borne Haber cycle is the formation of gaseous K from solid KBr. This requires energy, as indicated by the positive value of +89 kJ/mol.

Step 2: Ionization of gaseous K (K(g) → K+(g) + e-)
In this step, one electron is removed from gaseous K to form a K+ ion. This process requires energy, as indicated by the positive value of +420 kJ/mol.

Step 3: Formation of gaseous Br (Br(g))
The third step involves the formation of gaseous Br from solid KBr. This also requires energy, as indicated by the positive value of +112 kJ/mol.

Step 4: Electron affinity of gaseous Br (Br(g) + e- → Br-(g))
In this step, the gaseous Br atom gains an electron to form a Br- ion. This process releases energy, as indicated by the negative value of -342 kJ/mol.

Step 5: Formation of solid KBr (K+(g) + Br-(g) → KBr(s))
The final step in the Borne Haber cycle is the formation of solid KBr from gaseous K+ and Br- ions. This process releases energy, as indicated by the lattice enthalpy (-392 kJ/mol).

To calculate the lattice enthalpy, you can use Hess's law, which states that the overall enthalpy change of a reaction is independent of the route taken. This means that the sum of the energies involved in the individual steps should be equal to the overall enthalpy change.

In this case, the lattice enthalpy can be calculated as follows:

ΔHlattice = ΔH1 + ΔH2 + ΔH3 + ΔH4 + ΔH5
= (+89 kJ/mol) + (+420 kJ/mol) + (+112 kJ/mol) + (-342 kJ/mol) + (-392 kJ/mol)
= -113 kJ/mol

Therefore, the lattice enthal