Problem 75 - Chemistry Matter and Change

Question

Write chemical equations for these reactions. a. When solid naphthalene \(\left(\mathrm{C}_{10} \mathrm{H}_{8}\right)\) burns in air, the reaction yields gaseous carbon dioxide and liquid water. b. Bubbling hydrogen sulfide gas through manganese(II) chloride dissolved in water results in the formation of the precipitate manganese(II) sulfide and hydrochloric acid. c. Solid magnesium reacts with nitrogen gas to produce solid magnesium nitride. d. Heating oxygen difluoride gas yields oxygen gas and fluorine gas.

Step-by-Step Solution

Answer

a) \[ C_{10}H_8 + 12O_2 \rightarrow 10CO_2 + 4H_2O \] b) \[ H_2S + MnCl_2 \rightarrow MnS + 2HCl \] c) \[ 3Mg + N_2 \rightarrow Mg_3N_2 \] d) \[ 2OF_2 \rightarrow O_2 + 2F_2 \]

Step 1: Identify Reactants and Products

For each reaction, identify the starting materials (reactants) and the resulting substances (products). a) Reactants: Naphthalene (C_10H_8) and oxygen (O_2); Products: Carbon dioxide (CO_2) and water (H_2O). b) Reactants: Hydrogen sulfide (H_2S) and manganese(II) chloride (MnCl_2); Products: Manganese(II) sulfide (MnS) and hydrochloric acid (HCl). c) Reactants: Magnesium (Mg) and nitrogen (N_2); Product: Magnesium nitride (Mg_3N_2). d) Reactant: Oxygen difluoride (OF_2); Products: Oxygen (O_2) and fluorine (F_2).

Step 2: Write Unbalanced Equations

Express each reaction with chemical formulas: a) Naphthalene burn: C_{10}H_8 + O_2 ightarrow CO_2 + H_2O. b) Reaction of H_2S with MnCl_2: H_2S + MnCl_2 ightarrow MnS + HCl. c) Magnesium with nitrogen: Mg + N_2 ightarrow Mg_3N_2. d) Decomposition of OF_2: OF_2 ightarrow O_2 + F_2.

Step 3: Balance Chemical Equations

Make sure the number of each type of atom is the same on both sides of the equation. a) C_{10}H_8 + 12O_2 ightarrow 10CO_2 + 4H_2O. b) H_2S + MnCl_2 ightarrow MnS + 2HCl (already balanced). c) 3Mg + N_2 ightarrow Mg_3N_2. d) 2OF_2 ightarrow O_2 + 2F_2.

Key Concepts

Reactants and Products

In any chemical reaction, the substances that start the process are known as reactants. They are transformed through the reaction into new substances, which are called products. Understanding the concept of reactants and products is crucial for writing chemical equations.

For instance, in the provided exercise:

• In reaction a, the reactants are naphthalene \(\mathrm{C}_{10}\mathrm{H}_8\) and oxygen \(\mathrm{O}_2\). The products, carbon dioxide \(\mathrm{CO}_2\) and water \(\mathrm{H}_2\mathrm{O}\), result from combustion.
• In reaction b, hydrogen sulfide \(\mathrm{H}_2\mathrm{S}\) and manganese(II) chloride \(\mathrm{MnCl}_2\) react to produce manganese(II) sulfide \(\mathrm{MnS}\) and hydrochloric acid \(\mathrm{HCl}\).
• Reaction c involves magnesium \(\mathrm{Mg}\) and nitrogen \(\mathrm{N}_2\) yielding magnesium nitride \(\mathrm{Mg}_3\mathrm{N}_2\).
• In reaction d, oxygen difluoride \(\mathrm{OF}_2\) decomposes into oxygen \(\mathrm{O}_2\) and fluorine \(\mathrm{F}_2\).

Clearly identifying reactants and products is the first step towards successfully writing and balancing chemical equations.

Balancing Equations

Once you've identified the reactants and products, the next step is to ensure that the number of atoms for each element is the same on both sides of the chemical equation. This complies with the Law of Conservation of Mass, which states that matter cannot be created or destroyed.

Here’s how balancing works in our examples:

• In reaction a: The equation \(\mathrm{C}_{10}\mathrm{H}_8 + 12\mathrm{O}_2 \rightarrow 10\mathrm{CO}_2 + 4\mathrm{H}_2\mathrm{O}\) balances carbon, hydrogen, and oxygen atoms.
• Reaction b: \(\mathrm{H}_2\mathrm{S} + \mathrm{MnCl}_2 \rightarrow \mathrm{MnS} + 2\mathrm{HCl}\) is already balanced.
• Reaction c: \(3\mathrm{Mg} + \mathrm{N}_2 \rightarrow \mathrm{Mg}_3\mathrm{N}_2\) balances magnesium and nitrogen atoms by adjusting the number of magnesium atoms.
• Reaction d: To balance \(2\mathrm{OF}_2 \rightarrow \mathrm{O}_2 + 2\mathrm{F}_2\), fluorine and oxygen atoms are balanced by adjusting the coefficients.

Balancing equations requires practice, but it becomes intuitive once you understand the process and practice it regularly.

Types of Chemical Reactions

Chemical reactions can be categorized into different types, each with its unique characteristics and patterns. In this exercise, several types of reactions are demonstrated:

• Combustion Reaction: Reaction a showcases a combustion reaction, where naphthalene combusts in the presence of oxygen to form carbon dioxide and water.
• Double Replacement Reaction: Reaction b is a double replacement reaction, involving an exchange of ions between hydrogen sulfide and manganese(II) chloride to produce manganese(II) sulfide and hydrochloric acid.
• Synthesis Reaction: In reaction c, magnesium and nitrogen combine in a synthesis reaction to form magnesium nitride.
• Decomposition Reaction: Reaction d illustrates a decomposition reaction, where oxygen difluoride breaks down into simpler substances, oxygen, and fluorine.

Understanding these types helps predict the products of reactions and grasp the underlying chemical changes.

Combustion Reactions

Combustion reactions are a type of chemical reaction where a substance combines with oxygen, releasing energy in the form of heat or light. These are exothermic reactions, meaning they release energy.

Common characteristics of combustion reactions include:

• Presence of Oxygen: Oxygen acts as the reactant that the other substance combusts with.
• Products: Usually produce carbon dioxide (\(\mathrm{CO}_2\)) and water (\(\mathrm{H}_2\mathrm{O}\)) when hydrocarbons are burned.
• Energy Release: The reaction is accompanied by the liberation of heat and sometimes light, which is why combustion is frequently observed with flames.

In the exercise example, naphthalene undergoes a combustion reaction to form carbon dioxide and water, following the general pattern where a hydrocarbon reacts with oxygen.Combustion reactions are not only important in understanding chemical processes but are also vital in everyday applications such as heating and powering vehicles.