Problem 21 - Chemistry Matter and Change

Question

$$\mathrm{K}(\mathrm{s})+\mathrm{ZnCl}_{2}(\mathrm{aq}) \rightarrow$$

Step-by-Step Solution

Answer

The products are potassium chloride (KCl) and zinc (Zn), balanced as: \( 2\text{K} + \text{ZnCl}_2 \rightarrow 2\text{KCl} + \text{Zn} \).

Step 1: Identify Reactants

The reactants in the given equation are potassium (K) solid and zinc chloride (ZnCl₂) aqueous.

Step 2: Determine the Reaction Type

This is a single replacement reaction (also known as a single displacement reaction), where a more reactive metal replaces a less reactive metal in a compound.

Step 3: Check Reactivity Series

Potassium (K) is more reactive than zinc (Zn) in the reactivity series, so it can displace zinc from zinc chloride (ZnCl₂).

Step 4: Write the Products of the Reaction

In a single replacement reaction of K replacing Zn, the products will be potassium chloride (KCl) and zinc metal (Zn). The balanced chemical equation is: \[ 2\text{K} + \text{ZnCl}_2 \rightarrow 2\text{KCl} + \text{Zn} \]

Step 5: Balance the Equation

The unbalanced products from the reaction are potassium chloride and zinc. To balance the equation, we adjust the coefficients to ensure that the number of atoms for each element is equal on both sides.- Reactants: K: 2, Zn: 1, Cl: 2- Products: K: 2, Zn: 1, Cl: 2The final balanced equation remains the same: \[ 2\text{K} + \text{ZnCl}_2 \rightarrow 2\text{KCl} + \text{Zn} \]

Key Concepts

Reactivity Series

The reactivity series is a list that ranks elements based on their ability to displace other elements in chemical reactions. It is particularly useful in predicting the outcomes of single replacement reactions. In this series, metals are ordered by their reactivity with other substances like acids, water, and salts.
- More reactive metals, such as potassium ({K} ), can displace less reactive metals from a compound. - Less reactive metals, like gold or silver, do not easily participate in such reactions.
For instance, in our exercise problem, we see potassium ({K}) and zinc ({Zn}). Potassium is significantly more reactive than zinc. This means that when {K} is introduced to zinc chloride ({ZnCl}_2), it will displace zinc due to its higher position in the reactivity series. Understanding this concept is fundamental to anticipating how metals will behave in chemical reactions.

Balancing Chemical Equations

Balancing chemical equations is crucial to accurately represent a chemical reaction. The law of conservation of mass states that matter cannot be created or destroyed in a reaction. That means the number of atoms of each element must remain constant on both sides of the equation.
To balance an equation:

• Start by listing all the elements involved on both sides of the equation.
• Count the number of atoms for each element in the reactants and products.
• Adjust the coefficients to make sure the number of atoms is the same on both sides.

In our example: {2K + ZnCl_2 ightarrow 2KCl + Zn}:

• There are 2 potassium (K) atoms on both sides, ensuring balance.
• There is 1 zinc (Zn) atom on both sides.
• There are 2 chlorine (Cl) atoms on both sides.

The balanced equation reflects the stoichiometry of the reaction, ensuring that it adheres to the conservation of mass.

Reactants and Products Identification

Identifying reactants and products is the first step in understanding any chemical reaction. It helps in setting up the equation that needs solving.
In a chemical equation: - **Reactants** are the substances you start with. They are the ingredients that undergo chemical change. - **Products** are the new substances formed as a result of the reaction.
In the exercise given: - The **reactants** are potassium ({K}) in solid form and zinc chloride ({ZnCl}_2) in aqueous form. - The **products** are potassium chloride ({KCl}) and zinc metal ({Zn}). Identifying these correctly allows chemists to predict the outcome of reactions and balance them effectively, ensuring that the equation accurately represents the chemical process taking place.