Problem 19 - Chemistry: Principles and Reactions

Question

Complete and balance the following equations. If no reaction occurs, write NR. (a) \(\mathrm{Cl}_{2}(g)+\mathrm{I}^{-}(a q) \longrightarrow\) (b) \(\mathrm{F}_{2}(g)+\mathrm{Br}^{-}(a q) \longrightarrow\) (c) \(\mathrm{I}_{2}(s)+\mathrm{Cl}^{-}(a q) \longrightarrow\) (d) \(\mathrm{Br}_{2}(l)+\mathrm{I}^{-}(a q) \longrightarrow\)

Step-by-Step Solution

Answer

(a) Cl2(g) + I⁻(aq) (b) F2(g) + Br⁻(aq) (c) I2(s) + Cl⁻(aq) (d) Br2(l) + I⁻(aq) Answer: (a) Yes, the reaction will occur. The balanced chemical equation is: Cl₂(g) + 2I⁻(aq) ⟶ 2Cl⁻(aq) + I₂(s) (b) Yes, the reaction will occur. The balanced chemical equation is: F₂(g) + 2Br⁻(aq) ⟶ 2F⁻(aq) + Br₂(l) (c) No, the reaction will not occur. (d) Yes, the reaction will occur. The balanced chemical equation is: Br₂(l) + 2I⁻(aq) ⟶ 2Br⁻(aq) + I₂(s)

Step 1: Use the activity series to determine possible reactions

For each of the given equations (a) to (d), we will use the activity series of halogens mentioned above to determine whether a halogen can replace another halogen in the compound.

Step 2: (a) Determine the reaction for Cl2(g) + I⁻(aq)

Chlorine (Cl₂) is higher in the activity series than Iodine (I₂) and therefore can replace Iodine in the compound. So a reaction will occur.

Step 3: (a) Complete and balance the reaction for Cl2(g) + I⁻(aq)

Cl₂(g) + 2I⁻(aq) ⟶ 2Cl⁻(aq) + I₂(s)

Step 4: (b) Determine the reaction for F2(g) + Br⁻(aq)

Fluorine (F₂) is higher in the activity series than Bromine (Br₂) and therefore can replace Bromine in the compound. So a reaction will occur.

Step 5: (b) Complete and balance the reaction for F2(g) + Br⁻(aq)

F₂(g) + 2Br⁻(aq) ⟶ 2F⁻(aq) + Br₂(l)

Step 6: (c) Determine the reaction for I2(s) + Cl⁻(aq)

Iodine (I₂) is lower in the activity series than Chlorine (Cl₂) and therefore cannot replace Chlorine in the compound. So no reaction will occur.

Step 7: (c) Write NR for no reaction

I₂(s) + Cl⁻(aq) ⟶ NR

Step 8: (d) Determine the reaction for Br2(l) + I⁻(aq)

Bromine (Br₂) is higher in the activity series than Iodine (I₂) and therefore can replace Iodine in the compound. So a reaction will occur.

Step 9: (d) Complete and balance the reaction for Br2(l) + I⁻(aq)

Br₂(l) + 2I⁻(aq) ⟶ 2Br⁻(aq) + I₂(s) The solutions for the given reactions are: (a) Cl₂(g) + 2I⁻(aq) ⟶ 2Cl⁻(aq) + I₂(s) (b) F₂(g) + 2Br⁻(aq) ⟶ 2F⁻(aq) + Br₂(l) (c) I₂(s) + Cl⁻(aq) ⟶ NR (d) Br₂(l) + 2I⁻(aq) ⟶ 2Br⁻(aq) + I₂(s)

Key Concepts

Activity Series

The activity series is an important tool in chemistry. It helps predict whether a chemical reaction will occur. In this case, it is used to determine if one halogen can displace another in a reaction. The series ranks elements based on their reactivity, with more reactive elements being able to replace less reactive ones.

• Fluorine (F₂) is the most reactive.
• It is followed by Chlorine (Cl₂), Bromine (Br₂), and Iodine (I₂) in decreasing order of reactivity.

This descending order means that if a higher halogen on the list is combined with a lower halogen in a compound, it can displace it. This is what determines if a reaction will occur or not in the given equations.

Balancing Equations

Balancing chemical equations is a fundamental skill in chemistry. It ensures that the same number of each type of atom is present on both sides of the equation. This reflects the Law of Conservation of Mass.
When balancing, follow these steps:

• Identify the number of atoms of each element in the reactants and products.
• Add coefficients to make these numbers equal.

For example, in reaction (a):

• You start with Cl₂ and I⁻.
• Chlorine displaces iodine, forming Cl⁻ and I₂.
• The balanced equation becomes Cl₂(g) + 2I⁻(aq) ⟶ 2Cl⁻(aq) + I₂(s), ensuring atom count is the same on both sides.

Balancing is crucial for depicting accurate chemical reactions and their stoichiometry.

Halogen Displacement

Halogen displacement reactions involve one halogen replacing another in a compound. This depends on the reactivity levels shown in the activity series. In our example:

• Chlorine can displace iodine because Chlorine is more reactive.

If the halogen attempting to displace another is higher up in the activity series, the reaction will proceed. An example of this is seen in reaction (d), where bromine (Br₂) displaces iodine (I⁻). These reactions are predictable because of the activity series. However, when iodine tries to displace chlorine as in (c), no reaction occurs since iodine is lower.
These displacement reactions are a subset of single replacement reactions.

Redox Reactions

Redox, or reduction-oxidation reactions, involve electron transfer. One substance loses electrons (oxidation) and another gains electrons (reduction). In halogen displacement reactions, the displaced halogen gains electrons and is reduced, while the displacing halogen loses electrons and is oxidized. For example, in reaction (d):

• Bromine (Br₂) gains electrons, is reduced to 2Br⁻.
• Iodine (I⁻) loses electrons, is oxidized to I₂.

Understanding redox reactions helps explain the movement of electrons during these chemical changes. It highlights the electron transfer which is a key concept in chemistry, especially in reactions involving metals and halogens. These processes are significant in various scientific fields and practical applications.