Which of the following would be exothermic reactions, why

Question

Na(g) Br(g) -> NaBr

Mg(g) -> Mg 2 2e-

MgCl2 -> Mg(s) CL2(g)

O(g) 2e- -> O2-

Cu(l) -> Cu(s)

Cu(s) -> Cu(g)

KF -> K F-

Cheers for the help..

Answer 1

exothermic reactions are the result of forming products that are more stable than the starting materials

Na(g) Br(g) -> NaBr

exothermic ... more stable products

Mg(g) -> Mg 2 2e-

exothermic ... more stable products

O(g) 2e- -> O2-

exothermic ... more stable products

Cu(l) -> Cu(s)

exothermic ... molten copper must lose energy to re-solidify