Problem 23 - Chemistry: The Central Science

Question

Write a balancedequation for the preparation of \(\mathrm{H}_{2}\) using (a) \(\mathrm{Mg}\) and an acid, (b) carbon and steam, (c) methane and steam.

Step-by-Step Solution

Answer

The balanced chemical equations for the preparation of hydrogen gas using the given methods are: (a) Mg + 2HCl → MgCl2 + H2 (b) C + H2O → CO + H2 (c) CH4 + H2O → CO + 3H2

Step 1: (a) Writing the balanced equation for the preparation of hydrogen gas using magnesium and an acid

The unbalanced chemical equation for this reaction is: Mg + HCl → MgCl2 + H2 To balance the equation, we need to ensure that the number of atoms of each element is the same on both sides of the equation. The balanced chemical equation is: Mg + 2HCl → MgCl2 + H2

Step 2: (b) Writing the balanced equation for the preparation of hydrogen gas using carbon and steam

The unbalanced chemical equation for this reaction is: C + H2O → CO + H2 To balance the equation, we need to ensure that the number of atoms of each element is the same on both sides of the equation. The balanced chemical equation is: C + H2O → CO + H2

Step 3: (c) Writing the balanced equation for the preparation of hydrogen gas using methane and steam

The unbalanced chemical equation for this reaction is: CH4 + H2O → CO + H2 To balance the equation, we need to ensure that the number of atoms of each element is the same on both sides of the equation. The balanced chemical equation is: CH4 + H2O → CO + 3H2

Key Concepts

Balanced Equations

Balanced equations are essential in chemical reactions. They show the reactants transforming into products while maintaining the law of conservation of mass. This law states that matter cannot be created or destroyed in a chemical reaction. Therefore, the number of atoms for each element must be the same on both sides of the equation. For instance, in the reaction of magnesium and hydrochloric acid to produce magnesium chloride and hydrogen gas, the unbalanced equation is:
Mg + HCl → MgCl2 + H2

• **Step 1:** Count the number of atoms of each element on both sides. Initially, we have 1 Mg, 1 Cl, and 2 H in the products, but only 1 Mg, 1 Cl, and 1 H in the reactants.
• **Step 2:** To balance, adjust the number of HCl molecules, resulting in: Mg + 2HCl → MgCl2 + H2.
• **Step 3:** Verify that each element is balanced: 1 Mg, 2 Cl, and 2 H on both sides.

This method ensures a balanced equation, respecting the conservation of mass law and accurately representing the chemical change.

Hydrogen Production

Hydrogen is a versatile element and a clean energy source. It can be produced through several chemical reactions. One common method is reacting magnesium with an acid, like hydrochloric acid, which results in hydrogen gas and a salt. Another method uses carbon and steam: - **Reaction with Carbon and Steam**: Carbon reacts with water vapor to produce hydrogen gas and carbon monoxide. The balanced equation is: C + H2O → CO + H2 This reaction is straightforward and illustrates the simplicity of hydrogen production using basic elements. Methane, the primary component of natural gas, can also produce hydrogen when reacted with steam: - **Reaction with Methane and Steam**: Methane, when exposed to water vapor, yields carbon monoxide and hydrogen gas. The balanced equation for this is: CH4 + H2O → CO + 3H2 Both processes are integral to industrial hydrogen production, highlighting the element's versatility and the efficiency of chemical reactions in generating useful compounds.

Reaction Stoichiometry

Reaction stoichiometry involves calculations based on balanced chemical equations. It helps determine the precise amount of reactants and products involved in a chemical reaction. For hydrogen production, understanding stoichiometry is crucial. Take the methane and steam reaction:
CH4 + H2O → CO + 3H2
Here, one molecule of methane reacts with one molecule of water to produce one molecule of carbon monoxide and three molecules of hydrogen gas. This ratio, derived from the balanced equation, lets chemists calculate:

• **Moles to Moles:** If you start with 2 moles of methane, you'll get 6 moles of hydrogen gas.
• **Mass Calculations:** Using molar masses, you can convert between grams of methane and grams of hydrogen produced.
• **Limiting Reactants:** Identify which reactant runs out first, thereby limiting the amount of product formed.

Stoichiometry provides a mathematical framework for predicting reaction outcomes, ensuring efficiency in chemical processes and optimizing resource use.