Question

The melting points for the compounds Li2S, Rb2S, and K2S are 900, 500, and 840 degrees C, respectively. Give the three compounds in order of increasing lattice energy

Answer 1

Answer: $Rb_2S$ < $K_2S$ < $Li_2S$

Explanation:

Lattice energy is the energy required to dissociate 1 mole of the an ionic compound into its constituent ions.

Thus higher is the lattice energy more energy will be required to melt the compounds.

As $Li_2S$  has highest melting point,  it will require most energy to melt an hence it will have highest lattice energy. The order of three compounds in order of increasing lattice energy

$Rb_2S$ < $K_2S$ < $Li_2S$