The reaction of calcium hydride, \(\mathrm{CaH}_{2}\), with water can be characterized as a Lewis acid-base reaction: \(\mathrm{CaH}_{2}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(a q)+2 \mathrm{H}_{2}(g)\) 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.

Oxidation-reduction reactions, also known as redox reactions, are processes that involve the transfer of electrons between two substances. An oxidation reaction is where a substance loses electrons and an oxidation state increases, while reduction is the gain of electrons leading to a decrease in oxidation state. Understanding these changes is crucial to grasp chemical reactions involving electron transfer.

For instance, when calcium hydride reacts with water, a redox reaction occurs alongside a Lewis acid-base interaction. Calcium hydride loses electrons (gets oxidized) while water gains those electrons (gets reduced), leading to the formation of calcium hydroxide and hydrogen gas. In simpler terms, a redox reaction in chemistry is like a dance of electrons from one partner to another, resulting in a new state of balance in the dancing couples, or the chemical entities. It's the push and pull of these chemical dances that drive the reactions forward.

To understand redox reactions, we must first be able to assign oxidation states to the elements in a chemical species. Oxidation states, often referred to as oxidation numbers, provide insight into the distribution of electrons among the atoms in a molecule.

We can determine oxidation states by following a set of rules: elements in their elemental form have an oxidation state of 0, and the sum of oxidation states in a neutral compound must equal 0. Monatomic ions have oxidation states equal to their charge. For instance, in our example of chemical oxidation-reduction, calcium in \(\mathrm{CaH}_{2}\) has an oxidation state of +2, hydrogen in \(\mathrm{CaH}_{2}\) is -1, and oxygen in water is -2, with hydrogen being +1. Applying these rules helps in tracking the movement of electrons during the redox process, making it easier to follow and predict the outcomes of reactions.

In every redox reaction, there are two key players: the oxidizing agent and the reducing agent. The oxidizing agent is the species that accepts electrons, thus gets reduced, while the reducing agent donates electrons and gets oxidized in the process.

Using our earlier example, water serves as the oxidizing agent because it gains electrons from calcium hydride, resulting in the reduction of its hydrogen atoms' oxidation state from +1 to -2. Conversely, calcium hydride acts as the reducing agent as it loses electrons, causing an increase in hydrogen's oxidation number from -1 to 0. Learning to identify these agents is like being a detective solving a mystery, where you follow the trail of electron clues to see which suspect 'took' electrons and which 'gave them away'—a fundamental skill in mastering chemistry.