Problem 13 - Chemistry and Chemical Reactivity

Question

Complete and balance the equations for the following reactions. [Assume an excess of oxygen for (d).] (a) \(\mathrm{Na}(\mathrm{s})+\mathrm{Br}_{2}(\ell) \longrightarrow\) (b) \(\mathrm{Mg}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow\) (c) \(\mathrm{Al}(\mathrm{s})+\mathrm{F}_{2}(\mathrm{g}) \longrightarrow\) (d) \(\mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow\)

Step-by-Step Solution

Answer

(a) \(2\, \mathrm{Na} + \mathrm{Br}_2 \rightarrow 2\, \mathrm{NaBr}\); (b) \(2\, \mathrm{Mg} + \mathrm{O}_2 \rightarrow 2\, \mathrm{MgO}\); (c) \(2\, \mathrm{Al} + 3\, \mathrm{F}_2 \rightarrow 2\, \mathrm{AlF}_3\); (d) \(\mathrm{C} + \mathrm{O}_2 \rightarrow \mathrm{CO}_2\).

Step 1: Understand the Reaction Types

Each of these reactions is a synthesis or combination reaction where two reactants combine to form a single product. We will write down the corresponding compound formulas formed by the elements.

Step 2: Balance Equation (a) Na and Br2

The reaction forms sodium bromide: \(\mathrm{Na} + \mathrm{Br}_2 \rightarrow \mathrm{NaBr}\). To balance, use 2 Na atoms to balance the Br atoms: \(2\, \mathrm{Na} + \mathrm{Br}_2 \rightarrow 2\, \mathrm{NaBr}\).

Step 3: Balance Equation (b) Mg and O2

The reaction forms magnesium oxide: \(\mathrm{Mg} + \mathrm{O}_2 \rightarrow \mathrm{MgO}\). Balance by adjusting the coefficient of Mg: \(2\, \mathrm{Mg} + \mathrm{O}_2 \rightarrow 2\, \mathrm{MgO}\).

Step 4: Balance Equation (c) Al and F2

The reaction forms aluminum fluoride: \(\mathrm{Al} + \mathrm{F}_2 \rightarrow \mathrm{AlF}_3\). Balance the equation: \(2\, \mathrm{Al} + 3\, \mathrm{F}_2 \rightarrow 2\, \mathrm{AlF}_3\).

Step 5: Balance Equation (d) C and O2

The reaction forms carbon dioxide: \(\mathrm{C} + \mathrm{O}_2 \rightarrow \mathrm{CO}_2\). This equation is already balanced: \(\mathrm{C} + \mathrm{O}_2 \rightarrow \mathrm{CO}_2\).

Key Concepts

Synthesis Reactions

In chemistry, synthesis reactions are a type of reaction where two or more simple substances combine to form a more complex substance. These reactions are also called combination reactions. Typically, the reactants are elements or simple compounds, and the product is a more complex compound. These reactions are straightforward because they usually involve the formation of a single product.

For example, when sodium (Na) reacts with bromine (\(\mathrm{Br}_2\)) in a synthesis reaction, they form sodium bromide (\(\mathrm{NaBr}\)). Similarly, magnesium (\(\mathrm{Mg}\)) reacts with oxygen (\(\mathrm{O}_2\)) to form magnesium oxide (\(\mathrm{MgO}\)). These reactions not only demonstrate the characteristics of synthesis reactions but also lay the foundation for understanding more complex chemical equations.

In general, synthesis reactions can be represented as:

• A + B → AB

This exemplifies the simplicity and predictability of synthesis reactions in chemistry. They are crucial in learning how substances can interact to form new compounds.

Reaction Balancing

Balancing chemical equations is an essential skill in chemistry as it ensures that the same number of each type of atom appears on both sides of the equation. This respect for the law of conservation of mass allows the reaction to adhere to natural chemical laws.

Consider the reaction between magnesium and oxygen to form magnesium oxide. Initially, the equation is \(\mathrm{Mg} + \mathrm{O}_2 \rightarrow \mathrm{MgO}\). However, upon inspecting the number of atoms, we see two oxygen atoms on the left but only one on the right. Therefore, we use coefficients to balance them: \(2 \mathrm{Mg} + \mathrm{O}_2 \rightarrow 2 \mathrm{MgO}\).

Here's a simple method to balance equations:

• Write down the number of atoms of each element in the reactants and products.
• Adjust coefficients to balance the atoms one by one, starting with atoms that appear in only one reactant and product.
• Double-check each element to ensure a balanced equation.

Balancing reactions helps chemists understand the stoichiometry of the reaction, predicting how much product can be formed from a given amount of reactants. It is fundamental for any further chemical calculations and reactions.

Chemical Equations

Chemical equations serve as a symbolic representation of a chemical reaction. They showcase the transformation of reactants into products, providing insight into how substances interact at the molecular level.

Each chemical equation follows a specific format, consisting of reactants on the left and products on the right. An arrow (\(\rightarrow\)) typically separates them, indicating the direction of the reaction. In the case of synthesis, the equations become simpler as fewer reactants come together to form a single product.

Let’s take the example of aluminum reacting with fluorine: \(\mathrm{Al} + \mathrm{F}_2 \rightarrow \mathrm{AlF}_3\). Initially, this equation is not balanced. By introducing coefficients, we adjust the equation to \(2 \mathrm{Al} + 3 \mathrm{F}_2 \rightarrow 2 \mathrm{AlF}_3\), maintaining equal numbers of each atom type on both sides.

Here are some features of chemical equations:

• Reactants and products must be clearly indicated.
• Symbols and formulas provide a concise representation of substances involved.
• Equations must be balanced in accordance with the conservation of mass.

Chemical equations are fundamental in chemistry, aiding in visualizing and predicting the results of chemical reactions. Understanding them is key to mastering chemistry concepts and conducting experiments effectively.