Problem 65 - Chemistry The Central Science In Si Units

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) \(\mathrm{Ca}(\mathrm{CN})_{2}(s)+\mathrm{HBr}(a q) \longrightarrow\)

Step-by-Step Solution

Answer

(a) \( \mathrm{ZnCO}_{3} \rightarrow \mathrm{ZnO} + \mathrm{CO}_{2} \), (b) \( \mathrm{BaC}_{2} + 2 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Ba(OH)}_{2} + \mathrm{C}_{2} \mathrm{H}_{2} \), (c) \( 2 \mathrm{C}_{2} \mathrm{H}_{2} + 5 \mathrm{O}_{2} \rightarrow 4 \mathrm{CO}_{2} + 2 \mathrm{H}_{2} \mathrm{O} \), (d) \( \mathrm{CS}_{2} + 3 \mathrm{O}_{2} \rightarrow \mathrm{CO}_{2} + 2 \mathrm{SO}_{2} \), (e) \( \mathrm{Ca}( ext{CN})_{2} + 4 \mathrm{HBr} \rightarrow \mathrm{CaBr}_{2} + 2 \mathrm{NH}_{3} \).

Step 1: Decompose Zinc Carbonate

Zinc carbonate \( \mathrm{ZnCO}_{3}(s) \) decomposes upon heating to form zinc oxide and carbon dioxide gas. The balanced reaction is:\[ \mathrm{ZnCO}_{3}(s) \stackrel{\Delta}{\longrightarrow} \mathrm{ZnO}(s) + \mathrm{CO}_{2}(g) \]

Step 2: Complete and Balance Reaction with Barium Carbide

Barium carbide reacts with water to produce barium hydroxide and acetylene gas. The correct balanced equation is:\[ \mathrm{BaC}_{2}(s) + 2 \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{Ba(OH)}_{2}(aq) + \mathrm{C}_{2} \mathrm{H}_{2}(g) \]

Step 3: Combust Acetylene

Acetylene combusts with oxygen to form carbon dioxide and water. The balanced chemical equation is:\[ 2 \mathrm{C}_{2} \mathrm{H}_{2}(g) + 5 \mathrm{O}_{2}(g) \rightarrow 4 \mathrm{CO}_{2}(g) + 2 \mathrm{H}_{2} \mathrm{O}(g) \]

Step 4: Combust Carbon Disulfide

Carbon disulfide combusts in oxygen to produce carbon dioxide and sulfur dioxide. The balanced equation is:\[ \mathrm{CS}_{2}(g) + 3 \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g) + 2 \mathrm{SO}_{2}(g) \]

Step 5: React Calcium Cyanamide with Hydrobromic Acid

Calcium cyanamide reacts with hydrobromic acid to form calcium bromide and ammonia. The balanced equation is:\[ \mathrm{Ca}( ext{CN})_{2}(s) + 4 \mathrm{HBr}(aq) \rightarrow \mathrm{CaBr}_{2}(aq) + 2 \mathrm{NH}_{3}(g) \]

Key Concepts

Chemical Reactions

At the heart of chemistry are chemical reactions, the processes where substances transform into new substances. These transformations occur due to the breaking and forming of chemical bonds. Each substance participating in the reaction, known as a reactant, is altered to yield products by the reaction's end.
Understanding chemical reactions involves:

• Identifying reactants and products
• Determining the chemical changes occurring
• Balancing the equation to follow the Law of Conservation of Mass

Balancing equations ensures that the same amount of each element exists on both sides of the equation, reflecting the conservation of matter during chemical processes.

Decomposition Reactions

A decomposition reaction occurs when a single compound breaks down into two or more simpler substances. This type of reaction is usually the result of the application of heat, light, or electricity to break the bonds within the compound.
In the exercise, zinc carbonate (\( \mathrm{ZnCO}_{3}(s) \) decomposes to form zinc oxide (\( \mathrm{ZnO}(s) \) and carbon dioxide (\( \mathrm{CO}_{2}(g) \). Decomposition reactions are vital in various industrial processes, such as the production of cement. Typically, they can be represented by the general formula:

• \( \mathrm{AB} \rightarrow \mathrm{A} + \mathrm{B}\)

This reaction highlights the principles of decomposition and shows the breakdown of a compound into simpler molecules or elements.

Combustion Reactions

Combustion reactions are exothermic processes that involve a substance reacting with oxygen to produce heat and light. They are easily recognized by the presence of oxygen as a reactant and carbon dioxide and water as products, particularly when hydrocarbons combust.
In the exercise, acetylene (\( \mathrm{C}_{2} \mathrm{H}_{2}(g) \) and carbon disulfide (\( \mathrm{CS}_{2}(g) \) each undergo combustion. They react with oxygen to produce gases like carbon dioxide and water or sulfur dioxide. The general formula for a combustion reaction, especially for hydrocarbons, is:

• \( \mathrm{C}_x \mathrm{H}_y + \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + \mathrm{H}_2 \mathrm{O}\)

These reactions support many everyday activities, from heating to powering engines.

Stoichiometry

Stoichiometry is the quantitative study of reactants and products in chemical reactions. It involves calculations to determine the proportions of elements within compounds and the ratios needed for reactions to proceed fully.

• In step 2, stoichiometry helps balance the numbers of water molecules and acetylene formed during the reaction with barium carbide.
• In steps 3 and 4, it ensures the correct amounts of oxygen are used during the combustion of both acetylene and carbon disulfide to obtain desired products.

Using stoichiometry, chemists calculate the exact amounts of reactants to mix to avoid wastage and ensure complete reactions. The balanced chemical equations are demonstrative of stoichiometry in action, used to maintain mass conservation and predict the outcomes of reactions.