Question

Complete and balance the following equations:$$ \begin{array}{l}{\text { (a) } \mathrm{ZnCO}_{3}(s) \stackrel{\Delta}{\longrightarrow}} \\ {\text { (b) } \mathrm{BaC}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow} \\ {\text { (c) } \mathrm{C}_{2} \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow}\end{array} $$ $$\begin{array}{l}{\text { (c) ~ } \mathrm{CS}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow} \\ {\text { (e) } \mathrm{Ca}(\mathrm{CN})_{2}(s)+\mathrm{HBr}(a q) \longrightarrow}\end{array}$$

Short answer

The short answers for the balanced chemical equations are as follows: (a) ZnCO_3(s) → ZnO(s) + CO_2(g) (b) BaC_2(s) + 2 H_2O(l) → C_2H_2(g) + Ba(OH)_2(s) (c) 2 C_2H_2(g) + 5 O_2(g) → 4 CO_2(g) + 2 H_2O(g) (d) CS_2(g) + 3 O_2(g) → CO_2(g) + 2 SO_2(g) (e) Ca(CN)_2(s) + 2 HBr(aq) → CaBr_2(aq) + 2 HCN(g)

Step-by-step solution

(a) ZnCO3(s) → ?

To balance the equation, identify the products formed when zinc carbonate (ZnCO_3) decomposes. Since a metal carbonate will decompose into its respective metal oxide and carbon dioxide, the balanced equation should look like this: ZnCO_3(s) → ZnO(s) + CO_2(g)

(b) BaC2(s) + H2O(l) → ?

Barium carbide (BaC_2) will react with water (H_2O) to form acetylene (C_2H_2) gas and barium hydroxide (Ba(OH)_2). The balanced equation for this reaction is: BaC_2(s) + 2 H_2O(l) → C_2H_2(g) + Ba(OH)_2(s)

(c) C2H2(g) + O2(g) → ?

Ethyne (C_2H_2), also known as acetylene, will react with oxygen (O_2) to form carbon dioxide (CO_2) and water (H_2O). To balance the equation, the coefficients should be adjusted to have equal numbers of atoms for each element on both sides: 2 C_2H_2(g) + 5 O_2(g) → 4 CO_2(g) + 2 H_2O(g)

(d) CS2(g) + O2(g) → ?

Carbon disulfide (CS_2) will react with oxygen (O_2) to form sulfur dioxide (SO_2) and carbon dioxide (CO_2). The balanced equation for this reaction is: CS_2(g) + 3 O_2(g) → CO_2(g) + 2 SO_2(g)

(e) Ca(CN)2(s) + HBr(aq) → ?

Calcium cyanide (Ca(CN)_2) will react with hydrobromic acid (HBr) to form calcium bromide (CaBr_2) and hydrogen cyanide (HCN). To balance the equation, the coefficients should be adjusted to have equal numbers of atoms for each element on both sides: Ca(CN)_2(s) + 2 HBr(aq) → CaBr_2(aq) + 2 HCN(g)

Key concepts

Stoichiometry

Stoichiometry is the heart of the chemistry that deals with the quantitative aspects of chemical reactions. This branch of chemistry is concerned with determining the proportions of elements that react to form products in a chemical equation. It is crucial for predicting yields of reactions and for figuring out how much of each reactant is needed to produce a desired amount of product.

When students engage in stoichiometry, they learn to balance chemical equations, interpret molar ratios, and calculate mass or volume of the reactants and products involved. In the textbook exercise, stoichiometry is applied to balance the decomposition and reaction equations, ensuring that the law of conservation of mass is honored—matter is neither created nor destroyed during a chemical reaction. To improve their grasp of stoichiometry, students should practice by predicting the products of given reactants and then confirming their predictions by balancing the resulting equations.

Chemical Reactions

Chemical reactions are processes where substances, called reactants, transform into different substances, known as products. They involve the breaking and making of chemical bonds and are represented by chemical equations that provide a symbolic depiction of the transformations taking place.

There are multiple types of chemical reactions, such as synthesis, decomposition, single replacement, double replacement, and combustion. In the exercise solutions, we encounter a variety of these reactions. For instance, when a compound like ZnCO_3 decomposes upon heating, this is an example of a decomposition reaction, while the reaction of Ca(CN)_2 with HBr is more aligned with a double replacement reaction. Understanding these categories helps students predict possible products and balance the equations accordingly. To improve comprehension, it's beneficial to apply the conservation of mass and charge, check that all atoms are accounted for, and that charges are balanced in ionic reactions.

Decomposition Reactions

Decomposition reactions are a type of chemical reaction where a single compound breaks down into two or more simpler substances. These reactions often require an input of energy, such as heat, light, or electricity. During decomposition, chemical bonds within the compound are broken, which leads to the creation of smaller products.

An example provided in the textbook exercise is the decomposition of ZnCO_3 into ZnO and CO_2. These reactions are not only pivotal in understanding chemical behavior but also hold importance in industrial processes, such as the production of cement and the extraction of metals from their ores. For students to further explore decomposition reactions, they can study factors that affect the rate of decomposition, including temperature, concentration, and the presence of catalysts. By doing so, their analytical skills in predicting and balancing decomposition reactions will be sharpened.