Lattice energy is defined as the energy required to break apart an ionic solid and convert its component atoms into gaseous ions. That is what you're doing in:
KCl (s) → K⁺(g) + Cl⁻(g)
The energy you require to obtain this reaction is 701 kJ/mol. As the value is positive, <em>energy would be absorbed.</em>
Subscripts cannot be changed because they are the ratio of the amount. And as we know, in a chemical equation/reaction, mass cannot be created nor destroyed. Therefore, we cannot change subscripts, however, we could change coefficients. <span />
