Question

Complete and balance each of the following decomposition reactions: (a) \(\mathrm{Li}_{2} \mathrm{CO}_{3}(s) \rightarrow\) (b) \(\mathrm{CdCO}_{3}(s) \rightarrow\)

Short answer

(a) \( ext{Li}_2 ext{CO}_3(s) \to ext{Li}_2 ext{O}(s) + ext{CO}_2(g)\) (b) \( ext{CdCO}_3(s) \to ext{CdO}(s) + ext{CO}_2(g)\)

Step-by-step solution

Understand Decomposition Reactions

Decomposition reactions involve a single compound breaking down into two or more simpler substances. Typically, carbonates decompose to form metal oxides and carbon dioxide gas when heated.

Decompose Li₂CO₃

Lithium carbonate, \( ext{Li}_2 ext{CO}_3\), decomposes when heated to form lithium oxide and carbon dioxide. The reaction is: \( ext{Li}_2 ext{CO}_3(s) ightarrow ext{Li}_2 ext{O}(s) + ext{CO}_2(g)\).

Balance the Equation for Li₂CO₃

Each element must have the same number of atoms on both sides of the equation. In \( ext{Li}_2 ext{CO}_3(s) ightarrow ext{Li}_2 ext{O}(s) + ext{CO}_2(g)\), lithium, carbon, and oxygen atoms are already balanced.

Decompose CdCO₃

Cadmium carbonate, \( ext{CdCO}_3\), decomposes to form cadmium oxide and carbon dioxide. The reaction is: \( ext{CdCO}_3(s) ightarrow ext{CdO}(s) + ext{CO}_2(g)\).

Balance the Equation for CdCO₃

Ensure that all elements have the same number of atoms on both sides. The equation \( ext{CdCO}_3(s) ightarrow ext{CdO}(s) + ext{CO}_2(g)\) is already balanced.

Key concepts

Chemical Equations

When we talk about chemical equations, we are looking at a way to express a chemical reaction using symbols and formulas. Imagine a recipe that tells you what ingredients are needed and what will be produced. A chemical equation does the same but for chemical reactions. Each part of the equation has a meaning: the left side lists the starting materials, known as reactants, and the right side lists the products, which are the new substances formed during the reaction. So, with the decomposition reactions such as those you're learning about with carbonates, you'll see the carbonate on the left and its decomposed products, typically a metal oxide and carbon dioxide, on the right.
When you read a chemical equation, take note of:

• The reactants and products and how they show what happens during the reaction.
• The physical states (solid, liquid, gas) which may be included in the equation for further clarity.
• Directional arrows, like \( \rightarrow \), indicating the direction of the reaction.

Remember, the way these elements and compounds are represented in an equation captures the essential details of the reaction.

Balancing Equations

Balancing chemical equations is a critical step in understanding reactions and ensuring they follow the law of conservation of mass. This law states that matter cannot be created or destroyed in a chemical reaction. Thus, each atom you start with as a reactant must appear in the same number in the products. Think of it as balancing a seesaw with children of the same weight on each side. It must be equal.
To balance equations:

• Write down the number of atoms for each element in both the reactants and the products.
• Adjust the coefficients (the numbers in front of compounds) until the number of atoms of each element is equal on both sides of the equation.
• Double-check your work to ensure you haven’t changed a subscript or formula, which can alter the compound itself.

You will see in the decomposition of carbonates like \( \mathrm{Li}_2 \mathrm{CO}_3 \) and \( \mathrm{CdCO}_3 \) that they often break down neatly into metal oxides and \( \mathrm{CO}_2 \) gas without needing additional balancing. Yet, always verify that everything matches perfectly for a complete and correct equation.

Carbonates Decomposition

Carbonates are compounds that contain carbonate ions \((\mathrm{CO}_3^{2-})\), and they tend to decompose when exposed to heat. This is a classic type of decomposition reaction where you generally end up with a metal oxide and carbon dioxide gas. For example, when lithium carbonate \( (\mathrm{Li}_2 \mathrm{CO}_3) \) decomposes, it splits into lithium oxide \( (\mathrm{Li}_2 \mathrm{O}) \) and carbon dioxide \( (\mathrm{CO}_2) \) gas.
This reaction can be visualized as:

• \[ \mathrm{Li}_2 \mathrm{CO}_3(s) \rightarrow \mathrm{Li}_2 \mathrm{O}(s) + \mathrm{CO}_2(g) \]

Similarly, cadmium carbonate \( (\mathrm{CdCO}_3) \) also decomposes to form cadmium oxide and carbon dioxide:

• \[ \mathrm{CdCO}_3(s) \rightarrow \mathrm{CdO}(s) + \mathrm{CO}_2(g) \]

Observing how these reactions occur helps you to make predictions about the behavior of other carbonates. It’s important to remember that decomposition reactions can differ in the temperature requirements for heating and in the stability of the products formed. This understanding is key when you're learning to write and balance these types of chemical equations.