Complete and balance the following equations: (a) \(\mathrm{K}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (b) \(\operatorname{NaH}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (c) \(\mathrm{Na}(s)+\mathrm{O}_{2}(g) \longrightarrow\) (d) \(\mathrm{K}(s)+\mathrm{O}_{2}(g) \longrightarrow\)

Chemical reactions are processes where reactants transform into products through the breaking and forming of chemical bonds.
Take equation (a) as an example, potassium (K) reacts with water (H2O) to produce potassium hydroxide (KOH) and hydrogen gas (H2). This transformation signifies a chemical change because the substances involved (K and H2O) change their chemical nature to become entirely new substances (KOH and H2).

It's critical to understand the reactants' and products' physical states, which in this case are solid (s), liquid (l), aqueous (aq), and gas (g). These notations provide insight into how substances interact in different states of matter, which is essential when performing experiments or solving problems in chemistry.

Stoichiometry is the area of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It is rooted in the principle that matter cannot be created or destroyed, which is reflected in the need to balance chemical equations.

For instance, in the step-by-step solution of equation (d), stoichiometry is used to balance the equation by ensuring that there is the same number of each type of atom on both sides of the equation. This is done by multiplying potassium (K) and potassium oxide (K2O) by coefficients that ensure the conservation of mass.

Importance of Stoichiometry in Chemistry

Understanding stoichiometry is crucial for predicting the outcomes of reactions, determining the proportions of materials needed, and in calculating the yields of chemical processes. It's a foundational concept that supports many applications in chemistry and related fields.

The law of conservation of mass states that mass in an isolated system is neither created nor destroyed by chemical reactions. Therefore, the mass of the reactants must equal the mass of the products.

In each of the balanced equations in the exercise, the total mass of the reactants equals the total mass of the products. For example, in equation (c), the mass of sodium (Na) and oxygen (O2) before the reaction equals the mass of sodium oxide (Na2O) after the reaction, once the equation is correctly balanced.

Applying the Law of Conservation of Mass

To apply this law in practice, as seen in the solutions provided, one must make sure that the number of atoms for each element is balanced on both sides of the reaction. This often requires adding coefficients to the chemical formulas in the equation, which can then be used to determine the amount of each substance involved in the reaction.