Question

Complete and balance the following equations. If no reaction occurs, write "N.R." (a) \(\mathrm{KCl}+\mathrm{Br}_{2} \longrightarrow\) (b) \(\mathrm{NaI}+\mathrm{Cl}_{2} \longrightarrow\) (c) \(\mathrm{KCl}+\mathrm{F}_{2} \longrightarrow\) (d) \(\mathrm{CaBr}_{2}+\mathrm{Cl}_{2} \longrightarrow\) (e) \(\mathrm{AlBr}_{3}+\mathrm{F}_{2} \longrightarrow\) (f) \(\mathrm{ZnBr}_{2}+\mathrm{I}_{2} \longrightarrow\)

Short answer

(a) N.R. (b) 2NaI + Cl2 -> 2NaCl + I2 (c) 2KCl + F2 -> 2KF + Cl2 (d) CaBr2 + Cl2 -> CaCl2 + Br2 (e) AlBr3 + 3F2 -> AlF3 + 3Br2 (f) N.R.

Step-by-step solution

- Analyze the Reactivity of Halogens

Determine the reactivity order of the halogens, which is F2 > Cl2 > Br2 > I2. A more reactive halogen will displace a less reactive halide from its compound.

- Apply the Reactivity Order to Each Reaction

Use the reactivity order to predict which reactions will occur, and then balance the resulting chemical equations using coefficients.

- Balance the Equations for Occurring Reactions

For the reactions that occur, apply the law of conservation of mass to balance each equation by adjusting coefficients to have the same number of atoms for each element on both sides of the equation.

- Identify Reactions That Do Not Occur

For reactions that do not occur because the halogen is not strong enough to displace the halide, write 'N.R.' to indicate no reaction.

- Complete and Balance Each Equation

For each equation, write the complete and balanced chemical equation or 'N.R.' if no reaction occurs. (a) N.R. (b) NaI + Cl2 -> 2NaCl + I2 (c) KCl + F2 -> 2KF + Cl2 (d) CaBr2 + Cl2 -> CaCl2 + Br2 (e) AlBr3 + F2 -> AlF3 + Br2 (f) ZnBr2 + I2 -> N.R.

Key concepts

Reactivity Series of Halogens

Understanding the reactivity series of halogens is crucial when it comes to predicting the outcomes of chemical reactions. The reactivity series orders halogens by their ability to displace other halogens from their compounds. Starting from the most reactive, it is Fluorine (F₂), followed by Chlorine (Cl₂), Bromine (Br₂), and Iodine (I₂).

This series is based on the tendency of a halogen to attract electrons, which decreases down the group as the atomic size increases. Therefore, when a compound with a less reactive halide (such as KCl which contains Cl⁻) is mixed with a more reactive halogen (like Br₂), a chemical reaction can occur whereby the more reactive halogen displaces the less reactive one. However, if the roles are reversed, and a less reactive halogen is introduced to a compound of a more reactive halide, no reaction takes place. This is because the less reactive halogen is not strong enough to displace the more reactive halide. This concept is essential for solving problems involving chemical reactions between halogens and halide compounds.

Law of Conservation of Mass

The law of conservation of mass states that in a chemical reaction, mass is neither created nor destroyed. This means that the total mass of the reactants must equal the total mass of the products. When balancing chemical equations, this law serves as a fundamental guideline, ensuring that the number of atoms of each element is conserved. In practice, you would adjust the coefficients—the numbers before the chemical formulas—to achieve the same number of atoms for each element on both sides of the reaction. For example, in reaction (b), the balanced equation is 2NaI + Cl₂ -> 2NaCl + I₂ because there are two sodium (Na) atoms, two iodine (I) atoms, and two chlorine (Cl) atoms on both the reactant and product sides. Balancing chemical equations is a foundational skill in chemistry that reflects the inherent balance in nature and upholds the law of conservation of mass.

Chemical Reaction Prediction

Predicting chemical reactions involves understanding how substances interact with each other. It requires knowledge of reactivity series, compound stability, solubility rules, and energetic considerations. By examining the reactants and considering these factors, chemists can predict the products of a reaction, or whether a reaction will occur at all. This prediction is not just a guess but is based on empirical rules and well-established principles.

For instance, when predicting reactions involving a more reactive halogen and a less reactive halide, one can expect the more reactive halogen to displace the less reactive one, resulting in a new compound. Conversely, if a reaction involves a less reactive halogen and a more reactive halide, the outcome is 'N.R.' indicating no reaction, as seen in reactions (a) and (f) from the exercise. In these cases, despite the potential for interaction, the less reactive element does not have the necessary reactivity to cause a change. Predicting chemical reactions is not only fascinating but is also practically significant in fields such as chemical engineering, pharmaceuticals, and environmental science.