Which element will react most vigorously with water, and what is the reaction that occurs?
(a) Lithium; 2 Li(s) + 2 H₂O(l) → 2 Li⁺(aq) + 2 H^–(aq) + H₂O₂(aq)
(b) Potassium; 2 K(s) + 2 H₂O(l) → 2 K⁺(aq) + 2 OH^–(aq) + H₂(g)
(c) Magnesium; Mg(s) + 2 H₂O(l) → Mg²⁺(aq) + 2 OH^–(aq) + H₂(g)
(d) Barium; Ba(s) + 2 H₂O(l) → Ba²⁺(aq) + 2 H^–(aq) + H₂O₂(aq)

Verified step by step guidance

1. Identify the group of elements in the periodic table that are known to react vigorously with water. Alkali metals, found in Group 1, are known for their vigorous reactions with water.
2. Compare the reactivity of the alkali metals listed in the options: Lithium (Li) and Potassium (K). Reactivity increases as you move down the group in the periodic table.
3. Consider the reaction equations provided for each element. The correct reaction for alkali metals with water should produce hydroxide ions (OH⁻) and hydrogen gas (H₂).
4. Analyze the given reactions: Option (b) for Potassium correctly shows the formation of K⁺, OH⁻, and H₂, which is typical for alkali metals reacting with water.
5. Conclude that Potassium (K) will react most vigorously with water, as it is lower in the group than Lithium and the reaction equation provided in option (b) is correct.

Key Concepts

Reactivity of Alkali Metals

Alkali metals, such as lithium, potassium, and barium, are known for their high reactivity, especially with water. This reactivity increases down the group in the periodic table, meaning potassium will react more vigorously than lithium. The reaction typically produces hydrogen gas and a corresponding hydroxide, which is a strong base.

Chemical Reactions with Water

When metals react with water, they can either displace hydrogen or form hydroxides. The general reaction for alkali metals involves the formation of metal hydroxides and hydrogen gas. For example, potassium reacts with water to produce potassium hydroxide and hydrogen, which is a characteristic reaction of alkali metals.

Balancing Chemical Equations

Balancing chemical equations is essential for accurately representing the conservation of mass in a reaction. Each side of the equation must have the same number of atoms for each element. Understanding how to balance equations helps in predicting the products and understanding the stoichiometry of the reaction, which is crucial for determining the most vigorous reaction with water.