Question #7b556

1 Answer
Dwight
Jan 30, 2018

The reaction will come down to a question of achieving lowest energy.

Explanation:

If the ionic bonding in the salt allows for a lower overall energy than the covalent bonding in the chlorine and metallic bonding in the sodium, the ionic solid is favoured.

I don't know whether we were asking for a quantitative analysis of this case, but I suspect your question was just a general one about why atoms that are already bonded would be expected to change their bonding.

It is possible to look up the values associated with the changes that are needed for this reaction to occur:

  • breaking the bond in the diatomic chlorine molecule is an energy-increasing process (endothermic)

    #Cl_2 rarr 2 Cl^-#

  • separating the Na metal into atoms requires energy as well (endothermic)

    #Na(s) rarr Na(g)#

  • transferring an electron from Na to Cl also costs energy (endothermic)

    #Na + Cl rarr Na^+ + Cl^-#

  • finally, having the #Na^+# ions and #Cl^-# ions bond together in a solid lattice (crystal) pattern is a large energy reduction (exothermic) process that brings the overall total to a lower value than existed at the start.

    #Na^+ + Cl^- 1 rarr NaCl(s)#

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