Question

Complete and balance the following equations: (a) \(\mathrm{Li}_{3} \mathrm{~N}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (b) \(\mathrm{NH}_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (c) \(\mathrm{NO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (d) \(\mathrm{NH}_{3}(g)+\mathrm{O}_{2}(g) \stackrel{\text { catalyst }}{\longrightarrow}\) (e) \(\mathrm{H}_{2} \mathrm{CO}_{3}(a q) \stackrel{\Delta}{\longrightarrow}\) (f) \(\mathrm{Ni}(s)+\mathrm{CO}(g) \longrightarrow\) (h) \(\mathrm{CS}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow\) (i) \(\mathrm{CaO}(s)+\mathrm{SO}_{2}(g) \longrightarrow\) (j) \(\mathrm{CH}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) \stackrel{\Delta}{\longrightarrow}\) (k) \(\mathrm{LiH}(s)+\mathrm{H}_{2} \mathrm{O}(t) \longrightarrow\) (1) \(\mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{H}_{2}(g) \longrightarrow\)

Short answer

(a) \(\mathrm{Li}_{3} \mathrm{N}(\mathrm{s})+\mathrm{3H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{3LiOH}(\mathrm{aq})+ \mathrm{NH}_{3}(\mathrm{g})\) (b) \(\mathrm{NH}_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{NH}_{4}^{+}(a q)+\mathrm{OH}^{-}(a q)\) (c) \(2 \mathrm{NO}_{2}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{HNO}_{3}(a q)+\mathrm{HNO}_{2}(a q)\) (d) \(4 \mathrm{NH}_{3}(g)+3 \mathrm{O}_{2}(g) \stackrel{\text { catalyst }}{\longrightarrow} 2 \mathrm{N}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(g)\) (e) \(\mathrm{H}_{2} \mathrm{CO}_{3}(a q) \stackrel{\Delta}{\longrightarrow} \mathrm{H}_{2} \mathrm{O}(l) + \mathrm{CO}_{2}(g)\) (f) \(\mathrm{Ni}(s)+4 \mathrm{CO}(g) \longrightarrow \mathrm{Ni(CO)_{4}(l)}\) (h) \(\mathrm{CS}_{2}(g)+3 \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+2 \mathrm{SO}_{2}(g)\) (i) \(\mathrm{CaO}(s) + \mathrm{SO}_{2}(g) \longrightarrow \mathrm{CaSO}_{4}(s)\) (j) \(\mathrm{CH}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) \stackrel{\Delta}{\longrightarrow} \mathrm{CO}(g)+3 \mathrm{H}_{2}(g)\) (k) \(\mathrm{LiH}(s)+\mathrm{H}_{2} \mathrm{O}(t) \longrightarrow \mathrm{LiOH}(a q)+\mathrm{H}_{2}(g)\) (1) \(\mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{H}_{2}(g) \longrightarrow \mathrm{2Fe}(s)+3 \mathrm{H}_{2} \mathrm{O}(g)\)

Step-by-step solution

(a) Balancing the Lithium Nitride and Water Reaction

In this equation, we have Lithium Nitride (\(\mathrm{Li}_{3} \mathrm{N}\)) reacting with water (\(\mathrm{H}_{2} \mathrm{O}\)).\ First, we need to predict the products of this reaction. Lithium is an alkali metal, and alkali metals react with water to give an alkali metal hydroxide and hydrogen gas. In this case, we'll have lithium hydroxide (\(\mathrm{LiOH}\)) and hydrogen gas (\(\mathrm{H}_{2}\)).\ Now we balance the equation:\ \(\mathrm{Li}_{3} \mathrm{N}(\mathrm{s})+\mathrm{3H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{3LiOH}(\mathrm{aq})+ \mathrm{NH}_{3}(\mathrm{g})\)

(b) Balancing the Ammonia and Water Reaction

Ammonia (\(\mathrm{NH}_{3}\)) reacts with water (\(\mathrm{H}_{2} \mathrm{O}\)) to produce ammonium ion (\(\mathrm{NH}_{4}^{+}\)) and hydroxide ion (\(\mathrm{OH}^{-}\)).\ The equation can be balanced as:\ \(\mathrm{NH}_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{NH}_{4}^{+}(a q)+\mathrm{OH}^{-}(a q)\)

(c) Balancing the Nitrogen Dioxide and Water Reaction

Nitrogen dioxide (\(\mathrm{NO}_{2}\)) reacts with water (\(\mathrm{H}_{2} \mathrm{O}\)) to form nitric acid (\(\mathrm{HNO}_{3}\)) and nitrous acid (\(\mathrm{HNO}_{2}\)).\ Now we balance the equation:\ \(2 \mathrm{NO}_{2}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{HNO}_{3}(a q)+\mathrm{HNO}_{2}(a q)\)

(d) Balancing the Ammonia and Oxygen Reaction

Ammonia (\(\mathrm{NH}_{3}\)) reacts with oxygen gas (\(\mathrm{O}_{2}\)) in the presence of a catalyst to produce nitrogen gas (\(\mathrm{N}_{2}\)) and water.\ We can balance the equation as follows:\ \(4 \mathrm{NH}_{3}(g)+3 \mathrm{O}_{2}(g) \stackrel{\text { catalyst }}{\longrightarrow} 2 \mathrm{N}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(g)\)

(e) Balancing the Carbonic Acid Reaction

Carbonic acid (\(\mathrm{H}_{2} \mathrm{CO}_{3}\)) decomposes upon heating into water (\(\mathrm{H}_{2} \mathrm{O}\)) and carbon dioxide gas (\(\mathrm{CO}_{2}\)).\ We can balance this equation as:\ \(\mathrm{H}_{2} \mathrm{CO}_{3}(a q) \stackrel{\Delta}{\longrightarrow} \mathrm{H}_{2} \mathrm{O}(l) + \mathrm{CO}_{2}(g)\)

(f) Balancing the Nickel and Carbon Monoxide Reaction

In this reaction, nickel (\(\mathrm{Ni}\)) reacts with carbon monoxide (\(\mathrm{CO}\)) to form nickel tetracarbonyl (\(\mathrm{Ni(CO)_{4}}\)).\ The equation can be balanced as:\ \(\mathrm{Ni}(s)+4 \mathrm{CO}(g) \longrightarrow \mathrm{Ni(CO)_{4}(l)}\)

(h) Balancing the Carbon Disulfide and Oxygen Reaction

Carbon disulfide (\(\mathrm{CS}_{2}\)) reacts with oxygen gas (\(\mathrm{O}_{2}\)) to produce sulfur dioxide (\(\mathrm{SO}_{2}\)) and carbon dioxide (\(\mathrm{CO}_{2}\)).\ We need to balance the equation:\ \(\mathrm{CS}_{2}(g)+3 \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+2 \mathrm{SO}_{2}(g)\)

(i) Balancing the Calcium Oxide and Sulfur Dioxide Reaction

Calcium oxide (\(\mathrm{CaO}\)) reacts with sulfur dioxide (\(\mathrm{SO}_{2}\)) to form calcium sulfate (\(\mathrm{CaSO}_{4}\)).\ The balanced equation is:\ \(\mathrm{CaO}(s) + \mathrm{SO}_{2}(g) \longrightarrow \mathrm{CaSO}_{4}(s)\)

(j) Balancing the Methane and Water Reaction

Methane (\(\mathrm{CH}_{4}\)) reacts with water (\(\mathrm{H}_{2} \mathrm{O}\)) upon heating to form carbon monoxide (\(\mathrm{CO}\)) and hydrogen gas (\(\mathrm{H}_{2}\)).\ We balance the equation:\ \(\mathrm{CH}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) \stackrel{\Delta}{\longrightarrow} \mathrm{CO}(g)+3 \mathrm{H}_{2}(g)\)

(k) Balancing the Lithium Hydride and Water Reaction

Lithium hydride (\(\mathrm{LiH}\)) reacts with water (\(\mathrm{H}_{2} \mathrm{O}\)) to form aqueous lithium hydroxide (\(\mathrm{LiOH}\)) and hydrogen gas (\(\mathrm{H}_{2}\)).\ The balanced equation is:\ \(\mathrm{LiH}(s)+\mathrm{H}_{2} \mathrm{O}(t) \longrightarrow \mathrm{LiOH}(a q)+\mathrm{H}_{2}(g)\)

(1) Balancing the Iron(III) Oxide and Hydrogen Reaction

Iron(III) oxide (\(\mathrm{Fe}_{2} \mathrm{O}_{3}\)) reacts with hydrogen gas (\(\mathrm{H}_{2}\)) to produce elemental iron (\(\mathrm{Fe}\)) and water (\(\mathrm{H}_{2} \mathrm{O}\)).\ We balance the equation:\ \(\mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{H}_{2}(g) \longrightarrow \mathrm{2Fe}(s)+3 \mathrm{H}_{2} \mathrm{O}(g)\)

Key concepts

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships of the reactants and products in a chemical reaction. It involves calculations that rely on the law of conservation of mass, which states that in a chemical reaction, matter is neither created nor destroyed. Thus, the amount of each element must be the same in both the reactants and products.

When solving stoichiometric problems, the first step is usually to write down the balanced chemical equation. This provides us with the stoichiometric coefficients that indicate the proportions in which reactants combine and products form. These coefficients are essential for converting between moles, mass, volume, and particles. A common stoichiometry exercise, like balancing the reaction between lithium nitride and water, involves determining the relative amounts of reactants and products to ensure the equation adheres to the law of conservation of mass.

In educational contexts, improving understanding of stoichiometry might focus on emphasizing the importance of the mole concept, the use of dimensional analysis (or factor-label method), and the relationship between moles, molar mass, and Avogadro's number.

Chemical Reactions

Chemical reactions are processes in which substances, known as reactants, transform into new substances, called products. There are various types of chemical reactions, including synthesis, decomposition, single replacement, double replacement, and combustion reactions.

In a synthesis reaction, multiple reactants combine to form a single product, as seen when lithium reacts with water to produce lithium hydroxide and hydrogen. Decomposition involves a single compound breaking down into two or more products, for example, carbonic acid decomposing into water and carbon dioxide.

Single replacement reactions involve one element taking the place of another in a compound, and double replacement reactions entail the exchange of ions between two compounds. Combustion typically refers to a reaction where a hydrocarbon burns in oxygen to produce carbon dioxide and water. Understanding the characteristics and outcomes of these reactions allows students to predict products and write balanced equations, a key element of mastering chemical equations.

Balancing Redox Reactions

Balancing redox reactions, or oxidation-reduction reactions, is a more complex aspect of stoichiometry that involves the transfer of electrons between substances. Redox reactions are identified by a change in the oxidation states of atoms.

In an oxidation process, an element loses electrons and its oxidation state increases, whereas in reduction, an element gains electrons, and its oxidation state decreases. For instance, when methane reacts with water to produce carbon monoxide and hydrogen, there is a transfer of electrons between carbon and hydrogen, demonstrating a redox process.

To balance redox equations, it is necessary to ensure not only the mass balance but also the charge balance. The half-reaction method is one approach, where the oxidation and reduction half-reactions are balanced separately for mass and charge before being combined to give the final balanced equation. Teaching the identification of oxidation states, the separation of half-reactions, and the use of electrons to balance charge can significantly aid students' understanding of the balancing of redox reactions.