Problem 25 - Chemistry: The Central Science

Question

Complete and balance the following equations: (a) \(\mathrm{NaH}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (b) \(\mathrm{Fe}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow\) (c) \(\mathrm{H}_{2}(g)+\mathrm{Br}_{2}(g) \longrightarrow\) (d) \(\mathrm{Na}(l)+\mathrm{H}_{2}(g)\) (c) \(\mathrm{PbO}(s)+\mathrm{H}_{2}(g)\)

Step-by-Step Solution

Answer

The balanced equations are: (a) \(\mathrm{NaH}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{NaOH}(a q)+\mathrm{H}_{2}(g)\) (b) \(\mathrm{Fe}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{FeSO}_{4}(a q)+\mathrm{H}_{2}(g)\) (c) \(\mathrm{H}_{2}(g)+\mathrm{Br}_{2}(g) \longrightarrow 2\mathrm{HBr}(g)\) (d) \(2\mathrm{Na}(l)+\mathrm{H}_{2}(g) \longrightarrow 2\mathrm{NaH}(s)\) (e) \(\mathrm{PbO}(s)+\mathrm{H}_{2}(g) \longrightarrow \mathrm{Pb}(s)+\mathrm{H}_{2}\mathrm{O}(l)\)

Step 1: Identify Reactants and Products

On the left side, we have reactants NaH (sodium hydride) and H2O (water). On the right side, we need to figure out the products.

Step 2: Determine Possible Products

Sodium hydride reacts with water to produce sodium hydroxide (NaOH) and hydrogen gas (H2). So, the complete equation will be: \(\mathrm{NaH}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{NaOH}(a q)+\mathrm{H}_{2}(g)\)

Step 3: Balance the Equation

The equation is already balanced in terms of the elements and their quantities. The balanced equation for reaction (a) is: \(\mathrm{NaH}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{NaOH}(a q)+\mathrm{H}_{2}(g)\) (b) \(\mathrm{Fe}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow\)

Step 1: Identify Reactants and Products

On the left side, we have reactants Fe (iron) and H2SO4 (sulfuric acid). On the right side, we need to figure out the products.

Step 2: Determine Possible Products

Iron reacts with sulfuric acid to produce iron(II) sulfate (FeSO4) and hydrogen gas (H2). So, the complete equation will be: \(\mathrm{Fe}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{FeSO}_{4}(a q)+\mathrm{H}_{2}(g)\)

Step 3: Balance the Equation

The equation is already balanced in terms of the elements and their quantities. The balanced equation for reaction (b) is: \(\mathrm{Fe}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{FeSO}_{4}(a q)+\mathrm{H}_{2}(g)\) (c) \(\mathrm{H}_{2}(g)+\mathrm{Br}_{2}(g) \longrightarrow\)

Step 1: Identify Reactants and Products

On the left side, we have reactants H2 (hydrogen gas) and Br2 (bromine gas). On the right side, we need to figure out the products.

Step 2: Determine Possible Products

Hydrogen gas reacts with bromine gas to produce hydrogen bromide (HBr). So, the complete equation will be: \(\mathrm{H}_{2}(g)+\mathrm{Br}_{2}(g) \longrightarrow 2\mathrm{HBr}(g)\)

Step 3: Balance the Equation

To balance the equation, we place a coefficient of 2 to HBr on the product side to balance the Br atoms. The balanced equation for reaction (c) is: \(\mathrm{H}_{2}(g)+\mathrm{Br}_{2}(g) \longrightarrow 2\mathrm{HBr}(g)\) (d) \(\mathrm{Na}(l)+\mathrm{H}_{2}(g)\)

Step 1: Identify Reactants and Products

On the left side, we have reactants Na (sodium) and H2 (hydrogen gas). On the right side, we need to figure out the products.

Step 2: Determine Possible Products

Sodium reacts with hydrogen gas to produce sodium hydride (NaH). So, the complete equation will be: \(2\mathrm{Na}(l)+\mathrm{H}_{2}(g) \longrightarrow 2\mathrm{NaH}(s)\)

Step 3: Balance the Equation

To balance the equation, we place a coefficient of 2 to Na and NaH on their respective sides. The balanced equation for reaction (d) is: \(2\mathrm{Na}(l)+\mathrm{H}_{2}(g) \longrightarrow 2\mathrm{NaH}(s)\) (e) \(\mathrm{PbO}(s)+\mathrm{H}_{2}(g)\)

Step 1: Identify Reactants and Products

On the left side, we have reactants PbO (lead oxide) and H2 (hydrogen gas). On the right side, we need to figure out the products.

Step 2: Determine Possible Products

Lead oxide reacts with hydrogen gas to produce lead metal (Pb) and water (H2O). So, the complete equation will be: \(\mathrm{PbO}(s)+\mathrm{H}_{2}(g) \longrightarrow \mathrm{Pb}(s)+\mathrm{H}_{2}\mathrm{O}(l)\)

Step 3: Balance the Equation

The equation is already balanced in terms of the elements and their quantities. The balanced equation for reaction (e) is: \(\mathrm{PbO}(s)+\mathrm{H}_{2}(g) \longrightarrow \mathrm{Pb}(s)+\mathrm{H}_{2}\mathrm{O}(l)\)

Key Concepts

Chemical Equations

A chemical equation is a symbolic representation of a chemical reaction, displaying the reactants that interact and the products that are formed. When sodium hydride reacts with water, for example, the chemical equation \( \mathrm{NaH}(s) + \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{NaOH}(aq) + \mathrm{H}_{2}(g) \) captures this process.

Writing a chemical equation involves stating the reactants on the left side and the products on the right, with an arrow pointing from reactants to products to indicate the direction of the reaction. It's crucial to note that the law of conservation of mass must be observed, meaning the same number of each type of atom must appear on both sides of the equation. Balancing this equation, step by step, ensures that this law is upheld.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions. It's based on the balanced chemical equations and the principle that matter is neither created nor destroyed during a chemical reaction. In stoichiometry, we use coefficients to balance the equation, as seen in the reaction \( 2\mathrm{Na}(l) + \mathrm{H}_{2}(g) \longrightarrow 2\mathrm{NaH}(s) \).

The coefficients indicate the relative amounts of each substance involved. Here, '2' before sodium (Na) and sodium hydride (NaH) indicates that two moles of sodium react with one mole of hydrogen gas to produce two moles of sodium hydride. By understanding stoichiometry, students can predict the amounts of products produced or the reactants required for a reaction.

Reactants and Products

Reactants are substances that start a chemical reaction and are found on the left side of a chemical equation. Products, on the other hand, are substances formed as a result of the reaction and are written on the right side. In the equation \( \mathrm{PbO}(s) + \mathrm{H}_{2}(g) \longrightarrow \mathrm{Pb}(s) + \mathrm{H}_{2}\mathrm{O}(l) \), lead oxide (PbO) and hydrogen gas (H2) are the reactants, while lead metal (Pb) and water (H2O) are the products.

Identifying reactants and products is the first step in balancing chemical equations. It is essential for students to not only recognize reactants and products but also to understand their role in the reaction. This understanding is the foundation for mastering topics in chemistry, such as determining reaction yields and understanding the mechanisms behind chemical reactions.