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.

Short answer

The balanced chemical equations are: a. \(\mathrm{C}_{10}\mathrm{H}_{8} + 12\mathrm{O}_{2} \rightarrow 10\mathrm{CO}_{2} + 4\mathrm{H}_{2}\mathrm{O}\) b. \(\mathrm{H}_{2}\mathrm{S} + \mathrm{MnCl}_{2} \rightarrow \mathrm{MnS} + 2\mathrm{HCl}\) c. \(3\mathrm{Mg} + \mathrm{N}_{2} \rightarrow \mathrm{Mg}_{3}\mathrm{N}_{2}\) d. \(2\mathrm{OF}_{2} \rightarrow \mathrm{O}_{2} + 2\mathrm{F}_{2}\)

Step-by-step solution

a. Combustion of naphthalene

Write the chemical formula for naphthalene, carbon dioxide, and water. Naphthalene: \(\mathrm{C}_{10}\mathrm{H}_{8}\) Carbon dioxide: \(\mathrm{CO}_{2}\) Water: \(\mathrm{H}_{2}\mathrm{O}\) Now, write the unbalanced equation: \[\mathrm{C}_{10}\mathrm{H}_{8} + \mathrm{O}_{2} \rightarrow \mathrm{CO}_{2} + \mathrm{H}_{2}\mathrm{O}\] Next, balance the equation by adjusting the coefficients: \[1\mathrm{C}_{10}\mathrm{H}_{8} + 12\mathrm{O}_{2} \rightarrow 10\mathrm{CO}_{2} + 4\mathrm{H}_{2}\mathrm{O}\] The balanced chemical equation for the combustion of naphthalene is: \[\mathrm{C}_{10}\mathrm{H}_{8} + 12\mathrm{O}_{2} \rightarrow 10\mathrm{CO}_{2} + 4\mathrm{H}_{2}\mathrm{O}\]

b. Reaction of hydrogen sulfide with manganese(II) chloride

Write the chemical formula for hydrogen sulfide, manganese(II) chloride, manganese(II) sulfide, and hydrochloric acid. Hydrogen sulfide: \(\mathrm{H}_{2}\mathrm{S}\) Manganese(II) chloride: \(\mathrm{MnCl}_{2}\) Manganese(II) sulfide: \(\mathrm{MnS}\) Hydrochloric acid: \(\mathrm{HCl}\) Now, write the unbalanced equation: \[\mathrm{H}_{2}\mathrm{S} + \mathrm{MnCl}_{2} \rightarrow \mathrm{MnS} + \mathrm{HCl}\] Next, balance the equation by adjusting the coefficients: \[1\mathrm{H}_{2}\mathrm{S} + 1\mathrm{MnCl}_{2} \rightarrow 1\mathrm{MnS} + 2\mathrm{HCl}\] The balanced chemical equation for the reaction of hydrogen sulfide with manganese(II) chloride is: \[\mathrm{H}_{2}\mathrm{S} + \mathrm{MnCl}_{2} \rightarrow \mathrm{MnS} + 2\mathrm{HCl}\]

c. Reaction of magnesium with nitrogen

Write the chemical formula for magnesium, nitrogen gas, and magnesium nitride. Magnesium: \(\mathrm{Mg}\) Nitrogen gas: \(\mathrm{N}_{2}\) Magnesium nitride: \(\mathrm{Mg}_{3}\mathrm{N}_{2}\) Now, write the unbalanced equation: \[\mathrm{Mg} + \mathrm{N}_{2} \rightarrow \mathrm{Mg}_{3}\mathrm{N}_{2}\] Next, balance the equation by adjusting the coefficients: \[3\mathrm{Mg} + 1\mathrm{N}_{2} \rightarrow 1\mathrm{Mg}_{3}\mathrm{N}_{2}\] The balanced chemical equation for the reaction of magnesium with nitrogen gas is: \[3\mathrm{Mg} + \mathrm{N}_{2} \rightarrow \mathrm{Mg}_{3}\mathrm{N}_{2}\]

d. Decomposition of oxygen difluoride

Write the chemical formula for oxygen difluoride, oxygen gas, and fluorine gas. Oxygen difluoride: \(\mathrm{OF}_{2}\) Oxygen gas: \(\mathrm{O}_{2}\) Fluorine gas: \(\mathrm{F}_{2}\) Now, write the unbalanced equation: \[\mathrm{OF}_{2} \rightarrow \mathrm{O}_{2} + \mathrm{F}_{2}\] Next, balance the equation by adjusting the coefficients: \[2\mathrm{OF}_{2} \rightarrow 1\mathrm{O}_{2} + 2\mathrm{F}_{2}\] The balanced chemical equation for the decomposition of oxygen difluoride is: \[2\mathrm{OF}_{2} \rightarrow \mathrm{O}_{2} + 2\mathrm{F}_{2}\]

Key concepts

Combustion Reactions

One of the most striking types of chemical reactions is combustion reactions. These are reactions where a substance, typically a hydrocarbon, reacts with oxygen to produce carbon dioxide and water, releasing energy in the form of heat and light. The general formula for a combustion reaction is CxHy + O2 → CO2 + H2O. An example encountered in everyday life is the burning of gasoline in an engine or the flicker of a candle wick.

In order to write and balance a combustion reaction, you'll first need to know the chemical formula of the fuel. In the exercise provided, solid naphthalene, a polyaromatic hydrocarbon consisting of ten carbon atoms and eight hydrogen atoms (C10H8), combusts in air. Once you have the unbalanced equation, as shown in the textbook solution, the next step is to balance the atoms on both sides, making sure the number of carbon, hydrogen, and oxygen atoms are the same. It can be challenging to balance these types of reactions, particularly with larger hydrocarbons, so it's a good practice to start by balancing the carbon and hydrogen atoms before the oxygen atoms, as oxygen is present in multiple reactants and products.

Precipitation Reactions

In contrast to the fiery spectacle of combustion reactions, precipitation reactions are quieter affairs that occur when two aqueous solutions combine to form an insoluble solid called a precipitate. These reactions are a cornerstone of chemistry because they allow for the selective removal of ions from the solution.

The formation of the precipitate can often be predicted using the solubility rules, which indicate which combinations of ions lead to solids. To write the balanced equation for a precipitation reaction, one must be aware of the initial reactants and the ionic compounds that may precipitate. In our example, hydrogen sulfide and manganese(II) chloride react to yield manganese(II) sulfide and hydrochloric acid. Once the solid precipitate is formed, as MnS, it is removed from the equational balance of ions in solution. The correct stoichiometry must then be determined to ensure the law of conservation of mass is upheld, which the textbook solution provides.

Chemical Reaction Balancing

The principle of the conservation of mass dictates that in a chemical reaction, mass is neither created nor destroyed. Therefore, a balanced chemical equation ensures that the number of atoms for each element is the same on both sides of the reaction. Chemical reaction balancing is a fundamental skill in chemistry that requires an understanding of stoichiometry and the ability to manipulate coefficients of the reactants and products.

In the step-by-step solutions provided, you can see examples of balanced equations. Achieving balance in chemical reactions sometimes requires trial and error, especially with more complex molecules or reactions involving multiple steps. An effective strategy to balance equations is to first balance elements that appear in only one reactant and one product, then balance the more widely distributed elements, and finally balance the oxygen and hydrogen atoms, which are often found in multiple reactants and products.

Decomposition Reactions

In a decomposition reaction, a single compound breaks down into two or more simpler substances. This type of chemical reaction is essentially the opposite of a synthesis reaction. To recognize a decomposition reaction, you'll typically see one reactant breaking down to form multiple products. Commonly observed in the electrolysis of water or the breakdown of organic matter, decomposition reactions can also occur when a compound is heated, which is depicted in our textbook example with oxygen difluoride (OF2).

To balance a decomposition reaction, as done in the provided solution, ensure that the number of atoms of each element is equal on both sides of the equation. Decomposition reactions may require you to recognize the likely products based on the reactant's chemical composition and then adjust the coefficients to balance the equation. In teaching these reactions, practical laboratory demonstrations can be very helpful for reinforcing the concepts.