Problem 48 - Chemistry: The Central Science in SI Units, Global Edition

Question

Write a balanced equation for each of the following reactions. (You may have to guess at one or more of the reaction products, but you should be able to make a reasonable guess, based on your study of this chapter.) (a) Hydrogen selenide can be prepared by reaction of an aqueous acid solution on aluminum selenide. (b) Sodium thiosulfate is used to remove excess \(\mathrm{Cl}_{2}\) from chlorine-bleached fabrics. The thiosulfate ion forms \(\mathrm{SO}_{4}^{2-}\) and elemental sulfur, while \(\mathrm{Cl}_{2}\) is reduced to \(\mathrm{Cl}^{-}\).

Step-by-Step Solution

Answer

The balanced chemical equations for the given reactions are: (a) 6HCl + Al2Se3 -> 3H2Se + 2AlCl3 (b) Na2S2O3 + 4Cl2 -> Na2SO4 + 8S + 2Cl^-

Step 1: (a) Identify reactants and products

For this reaction, we have: - Reactants: Aqueous acid solution (Hydrochloric acid - HCl) and Aluminum Selenide (Al2Se3) - Product: Hydrogen selenide (H2Se) Now let's write the unbalanced equation: HCl + Al2Se3 -> H2Se + ? We need to identify the second product, which consists of the remaining elements, aluminum and chlorine. As they can form a compound, we expect the second product to be aluminum chloride (AlCl3). The unbalanced equation is now: HCl + Al2Se3 -> H2Se + AlCl3

Step 2: (a) Balance the chemical equation

To balance this equation, we need to make sure the number of atoms for each element is the same on both sides of the equation. We have 2 Aluminum atoms, 3 Selenium atoms, and 1 Chlorine atom in the reactant side, and we need to adjust the coefficients accordingly. The balanced chemical equation is: 6HCl + Al2Se3 -> 3H2Se + 2AlCl3

Step 3: (b) Identify reactants and products

For this reaction, we have: - Reactants: Sodium thiosulfate (Na2S2O3) and Chlorine (Cl2) - Products: Sulfate ions (SO4^2-), Elemental sulfur (S), and Chloride ions (Cl-) To neutralize the charges, we make sulfate ions (SO4^2-) part of a compound with sodium ions (Na+). So, the product is sodium sulfate (Na2SO4). Now, let's write the unbalanced equation: Na2S2O3 + Cl2 -> Na2SO4 + S + Cl^-

Step 4: (b) Balance the chemical equation

To balance this equation, we need to make sure the number of atoms for each element is the same on both sides of the equation. We have 2 Sodium atoms, 2 Sulfur atoms, 3 Oxygen atoms, and 2 Chlorine atoms in the reactant side, and we need to adjust the coefficients accordingly. The balanced chemical equation is: Na2S2O3 + 4Cl2 -> Na2SO4 + 8S + 2Cl^-

Key Concepts

Balanced Equations

Balancing chemical equations is a crucial step in understanding chemical reactions. It ensures that the same number of each type of atom appears on both sides of the equation, maintaining the law of conservation of mass. For example, let's look at the reaction involving the aqueous acid solution and aluminum selenide.Before balancing, the unbalanced equation is: \[\text{HCl} + \text{Al}_2\text{Se}_3 \to \text{H}_2\text{Se} + \text{AlCl}_3\]To balance this equation, count the number of atoms for each element on both sides and adjust coefficients to obtain the same number of atoms for each element on both sides. After doing so, we find the balanced equation is:6\text{HCl} + \text{Al}_2\text{Se}_3 \to 3\text{H}_2\text{Se} + 2\text{AlCl}_3.Similarly, for the reaction between sodium thiosulfate and chlorine:Na\(_2\)S\(_2\)O\(_3\) + Cl\(_2\) \rightarrow Na\(_2\)SO\(_4\) + S + Cl\(^-\). Balancing gives us:Na\(_2\)S\(_2\)O\(_3\) + 4Cl\(_2\) \rightarrow Na\(_2\)SO\(_4\) + 8S + 2Cl\(^-\). This step ensures that the mass of reactants equals the mass of products, a key feature in chemical reactions.

Stoichiometry

Stoichiometry revolves around the calculation of reactants and products in chemical reactions. It helps in predicting the quantities of substances consumed or produced. To use stoichiometry effectively, you first need a balanced chemical equation.When a balanced equation is established, say from:6\text{HCl} + \text{Al}_2\text{Se}_3 \to 3\text{H}_2\text{Se} + 2\text{AlCl}_3,we can use it to determine the proportion of reactants and products. The coefficients tell us the ratio:

• 6 molecules of HCl react with 1 molecule of \( \text{Al}_2\text{Se}_3 \).
• This results in 3 molecules of \( \text{H}_2\text{Se} \) and 2 molecules of \( \text{AlCl}_3 \).

For the sodium thiosulfate and chlorine reaction, stoichiometry lets us determine how much sulfate, sulfur, and chloride ion is produced from given quantities of reactants:

• 1 molecule of Na\(_2\)S\(_2\)O\(_3\) reacts with 4 molecules of Cl\(_2\).
• This gives 1 molecule of Na\(_2\)SO\(_4\), 8 sulfur atoms, and 2 chlorine ions.

Thus, stoichiometry provides us a numerical framework to explore chemical processes.

Reaction Products

Reaction products are substances that are formed as a result of a chemical reaction. Identifying potential products often requires an understanding of the reactants involved and the possible interactions.For instance, in the reaction involving aluminum selenide and hydrochloric acid, we hypothesize hydrogen selenide and aluminum chloride as products based on our knowledge of chemical reactivity and compounds chemistry.In the reaction between sodium thiosulfate and chlorine, we identify sodium sulfate, sulfur, and chloride ions:

• Na\(_2\)SO\(_4\) forms due to the balancing of charges between sodium ions and sulfate ions.
• Elemental sulfur is a product as sulfur atoms rearrange during the reaction.
• Chloride ions are formed as \( \text{Cl}_2 \) is reduced during the reaction.

Overall, predicting reaction products involves understanding the types of bonds and interactions that govern the response of different elements and compounds in a reaction setting.