The reaction of calcium hydride,\({\rm{Ca}}{{\rm{H}}_{\rm{2}}}\), with water can be characterized as a Lewis acid-base reaction: \({\rm{Ca}}{{\rm{H}}_{\rm{2}}}\left( {\rm{s}} \right){\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\left( {\rm{l}} \right) \to {\rm{Ca}}{\left( {{\rm{OH}}} \right)_{\rm{2}}}\left( {{\rm{aq}}} \right){\rm{ + 2}}{{\rm{H}}_{\rm{2}}}\left( {\rm{g}} \right)\).

Identify the Lewis acid and the Lewis base among the reactants. The reaction is also an oxidation-reduction reaction. Identify the oxidizing agent, the reducing agent, and the changes in oxidation number that occur in the reaction.

A Lewis acid-base reaction is a chemical reaction that forms at least one covalent bond between an electron pair donor (Lewis base) and an electron pair acceptor (Lewis acid).

According to the Lewis theory, the substrate in a chemical reaction that receives an electron pair is considered an acid, while the substrate that loses an electron pair is a base.

Calcium hydride acts like a base and gives an electron to a water molecule, which is acidic in nature in the following reaction:

\({\rm{Ca}}{{\rm{H}}_{\rm{2}}}\left( {\rm{s}} \right){\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\left( {\rm{l}} \right) \to {\rm{Ca}}{\left( {{\rm{OH}}} \right)_{\rm{2}}}\left( {{\rm{aq}}} \right){\rm{ + 2}}{{\rm{H}}_{\rm{2}}}\left( {\rm{g}} \right).\)

Oxidation-reduction (redox) chemical reactions are reactionsduring which at least one element changes its oxidation number.

A hydrogenatomhas an oxidation number of -1 in calcium hydride and +1in awater molecule. Since the oxidation number in\({{\rm{H}}_2}\)is 0, this reaction is also a redox reaction.

Calcium hydride is a reducing agent, while water acts as an oxidizing agent.