Question

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

Short answer

(a) \( \mathrm{ZnCO}_{3}(s) \stackrel{\Delta}{\longrightarrow} \mathrm{ZnO}(s) + \mathrm{CO}_{2}(g) \) (b) \( \mathrm{BaC}_{2}(s) + 2\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ba(OH)}_{2}(s) + \mathrm{C}_{2} \mathrm{H}_{2}(g) \) (c) \( 2\mathrm{C}_{2} \mathrm{H}_{2}(g) + 5\mathrm{O}_{2}(g) \longrightarrow 4\mathrm{CO}_{2}(g) + 2\mathrm{H}_{2} \mathrm{O}(g) \) (d) \( \mathrm{CS}_{2}(g) + 3\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) + 2\mathrm{SO}_{2}(g) \) (e) \( \mathrm{Ca}(\mathrm{CN})_{2}(s) + 2\mathrm{HBr}(a q) \longrightarrow \mathrm{CaBr}_{2}(aq) + 2\mathrm{HCN}(g) \)

Step-by-step solution

(a) Completing and balancing ZnCO3 decomposition)

The given equation is the decomposition of zinc carbonate (ZnCO3). When ZnCO3 decomposes, it produces zinc oxide (ZnO) and carbon dioxide (CO2): \( \mathrm{ZnCO}_{3}(s) \stackrel{\Delta}{\longrightarrow} \mathrm{ZnO}(s) + \mathrm{CO}_{2}(g) \) Now, we need to balance the equation by adjusting the coefficients. In this case, the equation is already balanced, so the balanced equation is: \( \mathrm{ZnCO}_{3}(s) \stackrel{\Delta}{\longrightarrow} \mathrm{ZnO}(s) + \mathrm{CO}_{2}(g) \)

(b) Completing and balancing BaC2 + H2O reaction)

For the given equation, barium carbide (BaC2) reacts with water (H2O) to form barium hydroxide (Ba(OH)2) and acetylene gas (C2H2): \( \mathrm{BaC}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ba(OH)}_{2}(s) + \mathrm{C}_{2} \mathrm{H}_{2}(g) \) Now, we need to balance the equation by adjusting the coefficients. The balanced equation is: \( \mathrm{BaC}_{2}(s) + 2\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ba(OH)}_{2}(s) + \mathrm{C}_{2} \mathrm{H}_{2}(g) \)

(c) Balancing C2H2 + O2 reaction)

For the given equation, acetylene gas (C2H2) reacts with oxygen gas (O2) to form carbon dioxide (CO2) and water (H2O). The unbalanced reaction is: \( \mathrm{C}_{2} \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) + \mathrm{H}_{2} \mathrm{O}(g) \) Now we will balance the reaction by adjusting the coefficients: \( 2\mathrm{C}_{2} \mathrm{H}_{2}(g) + 5\mathrm{O}_{2}(g) \longrightarrow 4\mathrm{CO}_{2}(g) + 2\mathrm{H}_{2} \mathrm{O}(g) \)

(d) Balancing CS2 + O2 reaction)

In this equation, carbon disulfide (CS2) reacts with oxygen gas (O2) to form carbon dioxide (CO2) and sulfur dioxide (SO2). The unbalanced reaction is: \( \mathrm{CS}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) + \mathrm{SO}_{2}(g) \) Now, we need to balance the reaction by adjusting the coefficients: \( \mathrm{CS}_{2}(g) + 3\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) + 2\mathrm{SO}_{2}(g) \)

(e) Completing and balancing Ca(CN)2 + HBr reaction)

For the given equation, calcium cyanide (Ca(CN)2) reacts with hydrobromic acid (HBr) to form calcium bromide (CaBr2) and hydrogen cyanide (HCN). The unbalanced reaction is: \( \mathrm{Ca}(\mathrm{CN})_{2}(s)+\mathrm{HBr}(a q) \longrightarrow \mathrm{CaBr}_{2}(aq) + \mathrm{HCN}(g) \) Now, we need to balance the reaction by adjusting the coefficients: \( \mathrm{Ca}(\mathrm{CN})_{2}(s) + 2\mathrm{HBr}(a q) \longrightarrow \mathrm{CaBr}_{2}(aq) + 2\mathrm{HCN}(g) \)

Key concepts

Decomposition Reactions

Decomposition reactions are types of chemical reactions where a single compound breaks down into two or more simpler products. This process is often triggered by heat, light, or electricity.
For example, in the decomposition of zinc carbonate (ZnCO3), when heat (\( \Delta \)) is applied, it breaks down into zinc oxide (ZnO) and carbon dioxide (CO2). The reaction can be represented as follows:
- \( \mathrm{ZnCO}_{3}(s) \stackrel{\Delta}{\longrightarrow} \mathrm{ZnO}(s) + \mathrm{CO}_{2}(g) \)
Some key points to remember about decomposition reactions:

• They involve a single reactant.
• They often require an energy source to break bonds.
• They result in multiple products.

Understanding decomposition reactions is important in studying many chemical processes, including chemical synthesis and environmental chemistry.

Combustion Reactions

Combustion reactions are exothermic reactions where a substance, typically a hydrocarbon, reacts with oxygen to produce carbon dioxide, water, and energy in the form of heat or light.
In the case of the combustion of acetylene (C2H2), it combines with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O):
- \( 2\mathrm{C}_{2} \mathrm{H}_{2}(g) + 5\mathrm{O}_{2}(g) \longrightarrow 4\mathrm{CO}_{2}(g) + 2\mathrm{H}_{2} \mathrm{O}(g) \)
Notable aspects of combustion reactions include:

• They require a fuel and an oxidant (typically oxygen).
• They release large amounts of energy.
• They often produce flames as the reaction progresses.

Combustion reactions are crucial for various applications like power generation, engine operation, and more. Understanding them helps in designing better fuel-efficient systems.

Chemical Reactions

Chemical reactions signify the transformation of reactants into products involving the breaking and forming of chemical bonds. These are the cornerstone of chemistry.
Reactions are classified into types such as combination, decomposition, displacement, and combustion, among others. The following concepts are essential for chemical reactions:

• All reactions involve changes in energy.
• They may be endothermic (absorbing energy) or exothermic (releasing energy).
• Conservation of mass must hold, meaning the amount of each element remains constant before and after a reaction.

Chemical reactions are everywhere. They occur in biological systems, industrial processes, and natural phenomena. Grasping the nuances of these reactions aids in fields like medicine, engineering, and environmental science.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It provides a way to calculate the amounts of substances consumed and produced.
For a balanced chemical equation, stoichiometry helps determine:

• The amount of reactants needed to form a desired product.
• The proportion of products formed from specified reactants.
• The limit of reactants in a reaction (the limiting reagent).

For instance, in the reaction of barium carbide with water\[ \mathrm{BaC}_{2}(s) + 2\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ba(OH)}_{2}(s) + \mathrm{C}_{2} \mathrm{H}_{2}(g) \], stoichiometry guides us in knowing two moles of water are necessary to react fully with one mole of barium carbide.
Understanding stoichiometry enhances our capacity to predict outcomes of reactions and to plan efficient chemical processes.