Question

\( \mathrm{~Pb}\left(\mathrm{NO}_{3}\right)_{2}\) (lead (II) nitrate), upon sufficient heating, turns into \(\mathrm{PbO}\) (lead (II) oxide), oxygen gas, and nitrogen dioxide gas. Write a balanced equation for this reaction, and classify the reaction type.

Short answer

The balanced equation for the decomposition of lead (II) nitrate is \(\mathrm{2~Pb(NO_{3})_{2} \rightarrow 2~PbO + O_{2} + 4~NO_{2}}\), and this reaction is classified as a decomposition reaction.

Step-by-step solution

Identify the reactant and the products

The given exercise provides the starting reactant and mentioned the products formed. The reactant is lead (II) nitrate \(\mathrm{Pb(NO_{3})_{2}}\), and the products are lead (II) oxide (\(\mathrm{PbO}\)), oxygen gas (O\(_{2}\)), and nitrogen dioxide gas (\(\mathrm{NO_{2}}\)).

Write the unbalanced chemical equation

From the given information, we can now write the unbalanced chemical equation: \[\mathrm{Pb(NO_{3})_{2}} \rightarrow \mathrm{PbO} + \mathrm{O_{2}} + \mathrm{NO_{2}}\]

Balance the chemical equation

We need to ensure that the number of atoms of each element is equal on both sides of the equation. We can balance the equation by adjusting the coefficients in front of each species. \[\mathrm{2~Pb(NO_{3})_{2} \rightarrow 2~PbO + O_{2} + 4~NO_{2}}\] This balanced equation states that two moles of lead (II) nitrate decompose to form two moles of lead (II) oxide, one mole of oxygen gas, and four moles of nitrogen dioxide gas.

Classify the reaction type

There are several types of chemical reactions, including synthesis, decomposition, single displacement, double displacement, and combustion. In this reaction, a single reactant decomposes into multiple products on heating. This kind of reaction is called a decomposition reaction. The balanced equation for the decomposition of lead (II) nitrate and the classification of the reaction is: \[\mathrm{2~Pb(NO_{3})_{2} \rightarrow 2~PbO + O_{2} + 4~NO_{2}}\] (Decomposition reaction)

Key concepts

Chemical Equations

Think of a chemical equation as a recipe for a chemical reaction. Just like a recipe outlines the quantities and ingredients needed for making a cake, a chemical equation shows the reactants consumed and the products formed in a chemical reaction. In the case of our exercise, the 'ingredients' or reactants is lead (II) nitrate \(\mathrm{Pb(NO_{3})_{2}}\), and the 'cake' or products are lead (II) oxide \(\mathrm{PbO}\), oxygen gas \(\mathrm{O_{2}}\), and nitrogen dioxide \(\mathrm{NO_{2}}\).

The equation gives us a snapshot of the chemical change, providing information not only about the substances involved but also their relative amounts. It is crucial for these equations to be clear and representative of the actual reaction, as they serve as the foundation for understanding and applying chemical knowledge in everything from lab experiments to industrial processes.

Balancing Chemical Equations

Balancing chemical equations is much like ensuring that the scales are equal on both sides. It's a way to comply with the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. So, to balance an equation, we adjust the coefficients (these are the numbers before the chemical formulas), not the subscripts (numbers within the chemical formulas) to get the same number of atoms for each element on both sides.

For our lead (II) nitrate decomposition equation, we had to find the right coefficients that would make the atoms count for lead, nitrogen, and oxygen equal on both the reactant and product sides. After some trial and error, it turned out that doubling the lead (II) nitrate and the lead (II) oxide, and quadrupling the nitrogen dioxide, did the trick. Now, the equation is balanced, reflecting the actual atomic inventory of the reaction.

Reaction Classification

Classifying reactions helps chemists to categorize and predict the outcomes of different interactions. The five main classes are synthesis, decomposition, single displacement, double displacement, and combustion. In synthesis reactions, multiple reactants combine to form a single product. Decomposition is the opposite, with a single reactant breaking down into multiple products. Single displacement involves atoms of one element taking the place of another in a compound, while double displacement involves the exchange of ions between two compounds. Lastly, combustion involves a substance reacting with oxygen to form water and carbon dioxide (usually), releasing energy in the form of heat and light.

The exercise we've been considering is a classic example of a decomposition reaction. Here, the reactant, lead (II) nitrate, is heated up and breaks down into lead (II) oxide, oxygen, and nitrogen dioxide. Recognizing this reaction as a decomposition helps us anticipate the products and understand the conditions needed for the reaction to occur.