Question

Write a balanced equation for each of the following single-replacement reactions: (a) A soft, gray piece of lithium is added to water. (b) A small piece of barium is added to water.

Short answer

(a) 2Li + 2H\(_2\)O → 2LiOH + H\(_2\); (b) Ba + 2H\(_2\)O → Ba(OH)\(_2\) + H\(_2\).

Step-by-step solution

Understand the Reaction Type

This is a single-replacement reaction, where one element replaces another in a compound. In the case of metals reacting with water, typically hydrogen gas is released, and a metal hydroxide is formed.

Identify Reactants and Products for Lithium

When lithium (Li) is added to water (H\(_2\)O), it reacts to form lithium hydroxide (LiOH) and hydrogen gas (H\(_2\)). The unbalanced reaction is: Li + H\(_2\)O → LiOH + H\(_2\).

Balance the Lithium Equation

Ensure the number of each type of atom is the same on both sides of the equation. For lithium, the balanced chemical equation is: 2Li + 2H\(_2\)O → 2LiOH + H\(_2\).

Identify Reactants and Products for Barium

For the reaction involving barium (Ba), it reacts similarly with water to form barium hydroxide (Ba(OH)\(_2\)) and hydrogen gas (H\(_2\)). The unbalanced reaction is: Ba + H\(_2\)O → Ba(OH)\(_2\) + H\(_2\).

Balance the Barium Equation

Balance the equation by ensuring the atoms of each element are equal on both sides. The balanced chemical equation is: Ba + 2H\(_2\)O → Ba(OH)\(_2\) + H\(_2\).

Key concepts

Single Replacement Reactions

Single replacement reactions involve swapping one element in a compound with another element. In these reactions, a more reactive metal will replace a less reactive hydrogen in water or acids. Understanding the displacement hierarchy is important here. Metals like lithium and barium, which are at the top of the reactivity series, can easily displace hydrogen from water.


Here’s what happens during these reactions:

• The metal reacts with water.
• Hydrogen gas is released.
• A hydroxide of the metal is formed.

To visualize, if you take lithium and add it to water, the lithium will replace some of the hydrogen in water, forming lithium hydroxide and releasing hydrogen gas. The equation captures this transformation and enables chemists to predict the products of the reaction.

Metal Hydroxide Formation

When metals like lithium and barium react with water, they don't just replace hydrogen; they actually form metal hydroxides. These compounds are crucial in learning about single replacement reactions. Metal hydroxides are composed of metal ions and hydroxide ions (OH⁻).

In the case of lithium:

• Lithium reacts with water to form lithium hydroxide: LiOH
• Equation: 2Li + 2H\(_2\)O → 2LiOH + H\(_2\)

Barium follows a similar pattern but forms a slightly different hydroxide:

• Barium reacts with water to produce barium hydroxide: Ba(OH)\(_2\)
• Equation: Ba + 2H\(_2\)O → Ba(OH)\(_2\) + H\(_2\)

The formation of metal hydroxides indicates the new compound that resulted from the reaction. This process is vital for understanding how different metals interact with water and predict the products formed.

Chemical Equation Balancing

Balancing chemical equations ensures the law of conservation of mass holds. The number of each type of atom must be equal on both sides of the equation. This process can initially seem complex, but with practice, it becomes an important skill.Start by writing the unbalanced equation with all reactants and possible products. Then, adjust coefficients to ensure each element has the same number on both sides. For lithium reacting with water:

• Unbalanced equation: Li + H\(_2\)O → LiOH + H\(_2\)
• Balanced equation: 2Li + 2H\(_2\)O → 2LiOH + H\(_2\)

For barium:

• Unbalanced equation: Ba + H\(_2\)O → Ba(OH)\(_2\) + H\(_2\)
• Balanced equation: Ba + 2H\(_2\)O → Ba(OH)\(_2\) + H\(_2\)

In summary, balancing equations isn't just about juggling atoms. It's about ensuring the equation follows the physical laws, providing a clear depiction of how substances interact during chemical reactions.