Problem 15 - Chemistry The Central Science In Si Units

Question

Write balanced chemical equations corresponding to each of the following descriptions: (a) Potassium cyanide reacts with an aqueous solution of sulfuric acid to form hydrogen cyanide gas. (b) When an aqueous solution of ammonium nitrite \(\left(\mathrm{NH}_{4} \mathrm{NO}_{2}\right)\) reacts with an aqueous solution of potassium hydroxide, ammonia gas, water and metal nitrate is formed. (c) When hydrogen gas is passed over solid hot iron(III) oxide, the resulting reaction produces iron and gaseous water. (d) When liquid ethanoic acid \(\left(\mathrm{CH}_{3} \mathrm{COOH}\right)\) is combusted, carbon dioxide and water are formed.

Step-by-Step Solution

Answer

Balance each equation: (a) KCN reacts with \(\text{H}_2\text{SO}_4\); (b) \(\text{NH}_4\text{NO}_2\) with KOH; (c) \(\text{H}_2\) with \(\text{Fe}_2\text{O}_3\); (d) \(\text{CH}_3\text{COOH}\) with \(\text{O}_2\).

Step 1: Identify Reactants and Products for Reaction A

In reaction (a), potassium cyanide (\(\text{KCN}\)) reacts with sulfuric acid (\(\text{H}_2\text{SO}_4\)). The products formed are hydrogen cyanide gas (\(\text{HCN}\)) and the expected byproduct in the solution, which will be potassium sulfate (\(\text{K}_2\text{SO}_4\)).

Step 2: Write Balanced Equation for Reaction A

The balanced chemical equation for reaction (a) is: \[ 2 \text{KCN} + \text{H}_2\text{SO}_4 \rightarrow 2 \text{HCN(g)} + \text{K}_2\text{SO}_4 \]

Step 3: Identify Reactants and Products for Reaction B

In reaction (b), ammonium nitrite (\(\text{NH}_4\text{NO}_2\)) reacts with potassium hydroxide (\(\text{KOH}\)). The products are ammonia gas (\(\text{NH}_3\)), water (\(\text{H}_2\text{O}\)), and potassium nitrate (\(\text{KNO}_3\)).

Step 4: Write Balanced Equation for Reaction B

The balanced chemical equation for reaction (b) is: \[ \text{NH}_4\text{NO}_2 + \text{KOH} \rightarrow \text{NH}_3(g)+ \text{H}_2\text{O} + \text{KNO}_3 \]

Step 5: Identify Reactants and Products for Reaction C

In reaction (c), hydrogen gas (\(\text{H}_2\)) is passed over iron(III) oxide (\(\text{Fe}_2\text{O}_3\)) to form iron (\(\text{Fe}\)) and water vapor (\(\text{H}_2\text{O(g)}\)).

Step 6: Write Balanced Equation for Reaction C

The balanced chemical equation for reaction (c) is: \[ 3 \text{H}_2 + \text{Fe}_2\text{O}_3 \rightarrow 2 \text{Fe} + 3 \text{H}_2\text{O(g)} \]

Step 7: Identify Reactants and Products for Reaction D

In reaction (d), ethanoic acid (\(\text{CH}_3\text{COOH}\)) is combusted to form carbon dioxide (\(\text{CO}_2\)) and water (\(\text{H}_2\text{O}\)).

Step 8: Write Balanced Equation for Reaction D

The balanced chemical equation for reaction (d) is: \[ 2 \text{CH}_3\text{COOH} + 4 \text{O}_2 \rightarrow 4 \text{CO}_2 + 4 \text{H}_2\text{O} \]

Key Concepts

Chemical Reactions

Chemical reactions occur when substances, commonly referred to as reactants, undergo chemical changes to form new substances known as products. Each reaction involving chemical substances entails changes at the molecular level. Here, bonds between atoms in the reactants are broken, and new bonds are formed to create the products. For example, when sulfuric acid reacts with potassium cyanide, bonds in these compounds break and rearrange to form hydrogen cyanide and potassium sulfate.

Understanding chemical reactions is crucial not only in chemistry but also in daily life. From the rusting of iron to the digestion of food, reactions are all around us. Chemical equations are used to represent these reactions and help us understand them better. By learning to interpret these equations, we gain insights into the reactants and products involved and the quantities required for the reaction to occur.

• Reactants: Starting substances in a chemical reaction
• Products: New substances formed as a result of the reaction
• Reactions can be influenced by various factors like temperature and concentration

Identification of Reactants and Products

Before writing a chemical equation, it's important to identify the reactants and the products. This identification allows us to understand what substances are involved in the reaction and what are being created. Reactants are typically mentioned in the beginning, while products are listed at the end.

For instance, in the reaction where potassium cyanide reacts with sulfuric acid, potassium cyanide (\( ext{KCN} \)) and sulfuric acid (\( ext{H}_2 ext{SO}_4 \)) are the reactants. The products of this reaction are hydrogen cyanide (\( ext{HCN} \)) and potassium sulfate (\( ext{K}_2 ext{SO}_4 \)). Likewise, identifying the correct substances involved in any chemical reaction is the key starting point to balance and understand the chemical equation.

• Analyze the problem statement to distinguish reactants and products
• Often, the reactants are provided, and you must deduce possible products
• Reactants and products must be consistent with the description of the chemical reaction

Writing Equations

Writing chemical equations is an essential step for visualizing a chemical reaction. These equations consist of chemical formulas that represent the substances involved. A typical chemical equation will have reactants on the left side, products on the right, separated by an arrow indicating the direction of the reaction.

Consider the reaction: when ammonium nitrite reacts with potassium hydroxide, the chemical equation can be written as \( ext{NH}_4 ext{NO}_2 + ext{KOH} \rightarrow ext{NH}_3(g) + ext{H}_2 ext{O} + ext{KNO}_3 \). Here, plus signs are used to separate different reactants or products, and physical states (such as (g) for gas) are specified for clarity.

• Utilize correct chemical symbols and formulas for reactants and products
• Ensure proper arrows to show the direction of the reaction
• Include physical states where necessary for added detail

Chemical Equations Balancing

Balancing chemical equations is crucial because it ensures the Law of Conservation of Mass is upheld. This law states that mass cannot be created or destroyed in a chemical reaction, meaning the mass of reactants must equal the mass of products. To balance a chemical equation, each type of atom must have the same number on both sides of the equation.

Take, for example, the combustion of ethanoic acid: \( 2 ext{CH}_3 ext{COOH} + 4 ext{O}_2 \rightarrow 4 ext{CO}_2 + 4 ext{H}_2 ext{O} \). Each element appears in equal numbers on both sides of the equation, indicating a balanced process.

• Start balancing with the least common atoms or with elements that appear in only one reactant and one product
• Adjust coefficients to balance the number of atoms for each element
• Re-verify your balanced equation to ensure accuracy