Problem 9 - Introductory Chemistry Atoms First

Question

\(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{~s}) \stackrel{\text { Heat }}{\longrightarrow} \mathrm{PbO}(\mathrm{s})+\mathrm{NO}(\mathrm{g})+\mathrm{O}_{2}(g)\)

Step-by-Step Solution

Answer

When solid lead (II) nitrate (Pb(NO3)2) is heated, it undergoes thermal decomposition and breaks down into solid lead oxide (PbO), nitrogen monoxide gas (NO), and oxygen gas (O2). The balanced chemical equation for this process is: \[Pb(NO_{3})_{2}(s) \stackrel{\text{Heat}}{\longrightarrow} PbO(s) + NO(g) + O_{2}(g)\]

Step 1: Identify reactants and products

In the given chemical equation, we have one reactant and three products: Reactant: Lead (II) nitrate, which is represented by the chemical formula Pb(NO3)2 Products: Lead oxide (PbO), nitrogen monoxide (NO), and oxygen gas (O2)

Step 2: Interpret coefficients and states of the substances involved

In the balanced chemical equation, we can see that there are no numerical coefficients in front of the substances, meaning they all have a coefficient of 1. This indicates that one mole of lead (II) nitrate decomposes into one mole of each product. Regarding the states of the substances, we see that: - Lead (II) nitrate, Pb(NO3)2, is a solid (s) - Lead oxide, PbO, is also a solid (s) - Nitrogen monoxide, NO, is a gas (g) - Oxygen gas, O2, is also a gas (g)

Step 3: Describe the process of thermal decomposition

Based on the given information, the process of thermal decomposition of lead (II) nitrate is as follows: When lead (II) nitrate is heated, it breaks down into lead oxide, nitrogen monoxide, and oxygen gas. The solid lead (II) nitrate becomes solid lead oxide, while the nitrogen and oxygen molecules are released as gases.

Key Concepts

Chemical Reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances into another. In the provided exercise, thermal decomposition is the type of chemical reaction occurring. When lead (II) nitrate Pb(NO extsubscript{3}) extsubscript{2}(s) is heated, it undergoes thermal decomposition to form different substances, which are lead oxide, nitrogen monoxide, and oxygen. This means that lead (II) nitrate rearranges its molecular structure to produce new compounds.

Chemical reactions are essential because they describe how chemical substances change during chemical processes, which can be classified into various types such as synthesis, decomposition, single replacement, and double replacement reactions. In the case of thermal decomposition, a single reactant breaks down into multiple products using energy, which in this case is provided by heat.

Chemical Equation

A chemical equation is a symbolic representation of a chemical reaction. It shows reactants on one side, an arrow indicating the transformation, and products on the other side. In our exercise, the chemical equation is:

the reactant side: Pb(NO extsubscript{3}) extsubscript{2}(s) and the product side: PbO(s) + NO(g) + O extsubscript{2}(g) An arrow indicates that the reactants are transformed into products through heating. This arrow can often represent different processes, such as heating, pressure, or a catalyst, in different reactions.

This equation also provides information about the conservation of mass, which states that the mass of the reactants is equal to the mass of the products in a chemical reaction. In balanced chemical equations like this one, each type of atom is equal on both sides of the equation, which is consistent with the law of conservation of mass.

Reactants and Products

Reactants are the starting materials in a chemical reaction, while products are the substances formed as a result of the reaction. In the thermal decomposition of lead (II) nitrate,

• the reactant is lead (II) nitrate, Pb(NO extsubscript{3}) extsubscript{2}(s), which is initially present before heating.
• The products are lead oxide, PbO(s), nitrogen monoxide, NO(g), and oxygen gas, O extsubscript{2}(g).

This transformation involves breaking and forming chemical bonds, which requires energy. In thermal decomposition, the energy is in the form of heat.

Understanding reactants and products is key to predict what a chemical reaction will yield and aids in numerous scientific calculations and applications. It also helps determine the stoichiometry of a reaction, which is the calculation of the reactants and products in chemical reactions.

States of Matter

In chemistry, the state of matter of a substance tells us about its physical form under given conditions. In the provided chemical reaction, substances are identified by different states of matter: solid (s), liquid (l), gas (g), and aqueous (aq).

• Lead (II) nitrate and lead oxide are both in the solid state (s) before and after heating, respectively, indicating they do not change phases during the reaction.
• Nitrogen monoxide and oxygen are released as gases (g), showing that gases were produced during the thermal decomposition process.

The states of matter not only provide information on how reactants and products exist physically but also influence the rate and extent of chemical reactions. Gas reactions, for example, often proceed faster due to higher energy particles and less obstruction to movement compared to solids.