Problem 88 - Chemistry Matter and Change

Question

Write chemical equations for the following single-replacement reactions that might occur in water. If no reaction occurs, write \(N R\) in place of the products. $$\begin{array}{l}{\text { a. nickel + magnesium chloride } \rightarrow} \\\ {\text { b. calcium + copper(II) bromide } \rightarrow} \\ {\text { c. potassium + aluminum nitrate } \rightarrow} \\ {\text { d. magnesium }+\text { silver nitrate } \rightarrow}\end{array}$$

Step-by-Step Solution

Answer

a. NR; b. \(\text{Ca} + \text{CuBr}_2 \rightarrow \text{CaBr}_2 + \text{Cu}\); c. \(\text{3K} + \text{Al(NO}_3\text{)}_3 \rightarrow \text{3KNO}_3 + \text{Al}\); d. \(\text{Mg} + \text{2AgNO}_3 \rightarrow \text{Mg(NO}_3\text{)}_2 + \text{2Ag}\).

Step 1: Determine Reactivity Series

Before predicting the products, list the reactivity series of metals to determine which metal is more reactive. A single-replacement reaction will only occur if the free element is more reactive than the metal in the compound.

Step 2: Analyze Reaction a

Nickel (Ni) is less reactive than magnesium (Mg); hence, no reaction will occur. Write the result as \(NR\) (no reaction).

Step 3: Analyze Reaction b

Calcium (Ca) is more reactive than copper (Cu). Therefore, calcium will replace copper in the compound. The reaction is: \[\text{Ca} + \text{CuBr}_2 \rightarrow \text{CaBr}_2 + \text{Cu}\]

Step 4: Analyze Reaction c

Potassium (K) is more reactive than aluminum (Al). Therefore, potassium will replace aluminum in the compound. The reaction is: \[\text{3K} + \text{Al(NO}_3\text{)}_3 \rightarrow \text{3KNO}_3 + \text{Al}\]

Step 5: Analyze Reaction d

Magnesium (Mg) is more reactive than silver (Ag). Therefore, magnesium will replace silver in the compound. The reaction is: \[\text{Mg} + \text{2AgNO}_3 \rightarrow \text{Mg(NO}_3\text{)}_2 + \text{2Ag}\]

Key Concepts

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They show how substances, called reactants, convert into different substances, known as products. Understanding chemical equations is crucial for studying chemistry, as they illustrate how atoms and molecules interact.

• The reactants are the substances that start the reaction, and they are written on the left side of the equation.
• The products are the new substances formed, written on the right side of the equation.
• An arrow (\(\rightarrow\)) separates the reactants from the products, indicating the direction of the chemical reaction.

To balance a chemical equation, make sure the same number of atoms of each element are present on both sides of the equation. This reflects the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. The coefficients (numbers before the chemical formulas) adjust the quantity of each substance to ensure balance.

Reactivity Series

The reactivity series is a list of metals ranked by their reactivity. It helps predict the outcomes of single-replacement reactions, like the ones in the exercise.

• Metals at the top of the series are most reactive. They readily lose electrons to form positive ions.
• Metals at the bottom are less reactive and do not easily participate in reactions.
• This sequence allows chemists to predict which metals can replace others in compounds.

A single-replacement reaction occurs if the free element is more reactive than the metal within a compound. For instance, magnesium, higher in the series, can replace silver in silver nitrate, causing a reaction. However, nickel cannot replace magnesium in magnesium chloride because it is less reactive.

Metals in Chemistry

Metals play a critical role in chemistry, especially in reactions like single replacements. They possess characteristic properties:

• High conductivity: Metals tend to conduct heat and electricity efficiently.
• Malleability and ductility: They can be shaped or drawn into wires without breaking.
• Reactiveness: Different metals have varying levels of reactivity depending on their ability to lose or gain electrons.

Chemical reactions in metals often involve electron exchange, leading to potentially exciting transformations. Their position in the reactivity series directly influences their ability to participate in chemical reactions, revealing why some metals like potassium react more vigorously than, say, nickel.

Predicting Reactions

Predicting reactions involves understanding how substances interact and transform. For single-replacement reactions, this means examining the reactivity series to determine which reactions will occur.

• Identify the more reactive metal between the free element and the metal in a compound.
• If the free metal is more reactive, a replacement occurs, forming new products.
• If it is less active, no reaction occurs, indicated as \(NR\) (no reaction).

Consider reaction b from the exercise: calcium replaces copper because calcium is higher in the reactivity series. Knowing how to predict these changes helps anticipate reaction outcomes, a vital skill in fields like chemistry and materials science.