What is mean by old bonds broken
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When we make friends, we bond with them in various ways, but those bonds can be broken. When we no longer are friends with them, for whatever reason, we refer to it as " old bonds being broken "

Explanation:

Chemical reactions make and break the chemical bonds between molecules, resulting in new materials as the products of the chemical reaction. Breaking chemical bonds absorbs energy,while new bonds releases, energy with the overall chemical reaction being endothermic or exothermic.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-