Question

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

Short answer

(a) Balanced: \(2\mathrm{K}(s) + 2\mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2\mathrm{KOH}(aq) + \mathrm{H}_{2}(g)\) (b) Balanced: \(\mathrm{NaH}(s) + \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{NaOH}(aq) + \mathrm{H}_{2}(g)\) (c) Balanced: \(4\mathrm{Na}(s) + \mathrm{O}_{2}(g) \rightarrow 2\mathrm{Na}_{2}\mathrm{O}(s)\) (d) Balanced: \(4\mathrm{K}(s) + \mathrm{O}_{2}(g) \rightarrow 2\mathrm{KO}_{2}(s)\)

Step-by-step solution

Analyze Reaction Components for (a)

The reaction involves solid potassium (K) reacting with liquid water (H₂O). Potassium, being an alkali metal, typically reacts with water to form a hydroxide and hydrogen gas. Therefore, the expected products are potassium hydroxide (KOH) and hydrogen gas (H₂).

Write and Balance Reaction for (a)

The unbalanced chemical equation is: \[\mathrm{K}(s) + \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{KOH}(aq) + \mathrm{H}_{2}(g)\]Balance it by ensuring the number of atoms for each element is equal on both sides. Balanced equation:\[2\mathrm{K}(s) + 2\mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2\mathrm{KOH}(aq) + \mathrm{H}_{2}(g)\]

Analyze Reaction Components for (b)

Sodium hydride (NaH) reacts with water to produce sodium hydroxide (NaOH) and hydrogen gas (H₂). NaH releases hydride ions when reacting with water, which forms hydrogen gas.

Write and Balance Reaction for (b)

The unbalanced chemical equation is:\[\mathrm{NaH}(s) + \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{NaOH}(aq) + \mathrm{H}_{2}(g)\]This equation is already balanced as written.

Analyze Reaction Components for (c)

Sodium (Na) reacts with oxygen (O₂) to form sodium oxide. As sodium can only form an oxide, not a peroxide, the product is sodium oxide (Na₂O).

Write and Balance Reaction for (c)

The unbalanced chemical equation is:\[\mathrm{Na}(s) + \mathrm{O}_{2}(g) \rightarrow \mathrm{Na}_{2}\mathrm{O}(s)\]Balance it by ensuring two sodium atoms react with one oxygen molecule:\[4\mathrm{Na}(s) + \mathrm{O}_{2}(g) \rightarrow 2\mathrm{Na}_{2}\mathrm{O}(s)\]

Analyze Reaction Components for (d)

Potassium (K) reacts with oxygen (O₂) to form potassium oxide. Potassium tends to form a peroxide known as potassium superoxide (KO₂) when it reacts with oxygen.

Write and Balance Reaction for (d)

The unbalanced chemical equation is:\[\mathrm{K}(s) + \mathrm{O}_{2}(g) \rightarrow \mathrm{KO}_{2}(s)\]Balance the reaction by ensuring four potassium atoms react with one oxygen molecule:\[4\mathrm{K}(s) + \mathrm{O}_{2}(g) \rightarrow 2\mathrm{KO}_{2}(s)\]

Key concepts

Balancing Equations

A fundamental skill in chemistry is the ability to balance chemical equations. This involves making sure the same number of each type of atom appears on both sides of an equation. When balancing equations:

• Identify the number of each atom in the reactants and products.
• Adjust coefficients (the numbers in front of compounds) to make the atoms balance.
• Never change subscripts (the small numbers in formulas that define the molecule).

Balancing chemical equations is essential because it reflects the Law of Conservation of Mass, which states that mass is neither created nor destroyed in a chemical reaction. This ensures that what goes into a reaction (the reactants) comes out to form the products in the same amount.

Reaction Components

When dealing with chemical reactions, it's crucial to understand the components involved. A chemical reaction involves reactants, which are substances that start the reaction, and products, which are substances formed as a result.

• Reactants are written on the left side of a chemical equation.
• Products are written on the right side of the chemical equation.

In our original exercise, the reactants and products in each equation must be clearly identified before attempting to balance the equation. This helps in predicting the reaction and ensuring the correct stoichiometry, i.e., the right proportions of reactants and products.

Alkali Metals Reactions

Alkali metals, such as sodium (Na) and potassium (K), are known for their high reactivity. When they come into contact with water or oxygen, they undergo vigorous reactions. In reactions with water:

• They form hydroxides, which are basic substances.
• Hydrogen gas is released as a by-product.

For instance, potassium reacts with water to form potassium hydroxide and hydrogen gas.
When alkali metals react with oxygen, they generally form oxides. Sodium forms sodium oxide, while potassium forms a superoxide. Understanding these common reaction patterns helps predict and balance the equations efficiently.

Chemical Products

Chemical products are the end-result substances formed in a reaction. Their nature depends on the specific reactants involved and the conditions of the reaction. Knowing the common products of a reaction especially helps in balancing equations effectively.

• In alkali metal and water reactions, expect hydroxides and hydrogen gas.
• In alkali metal and oxygen reactions, expect different types of oxides based on the specific metal.

For instance, in the reaction between sodium and oxygen, sodium oxide is formed. Recognizing the typical products that result from certain reactions aids chemists in predicting and writing balanced equations for complex chemical reactions.