Chemical reactions involve the breaking of chemical bonds, the rearrangement of elements, and the formation of new bonds. In order for a chemical reaction to take place, the particles must collide. The collision between the molecules in a chemical reaction provides the needed to break the necessary bonds so that new bonds can be formed. Successful collisions result in a chemical reaction that or energy. If the products have lower energy than the reactants, the reaction is and energy is If the reactants have lower energy than the products, the reaction is and energy is

The mass has escaped into a gas which you can not see so the law stays true.

Sorry i dont understand the question can you rephase it?

Electron equations of the given changes are as follow,a)                              cu      →      cu⁺²  + 2e⁻b)                              mg⁺²  +  2 e⁻      →      mgc)                              cl⁻    →      cl  +  1e⁻d)                              s  +  2 e⁻    →      s²⁻e)                                o²⁻      →      o  +  2 e⁻f)                              p  +  3 e⁻    →      p³⁻g)                              fe²⁺    →      fe³⁺  + 1 e⁻h)                              s²⁻    →      s⁴⁺  +  6 e⁻