Problem 21 - Chemistry and Chemical Reactivity

Question

Write balanced chemical equations for the reaction of hydrogen gas with oxygen, chlorine, and nitrogen.

Step-by-Step Solution

Answer

2H₂ + O₂ → 2H₂O; H₂ + Cl₂ → 2HCl; N₂ + 3H₂ → 2NH₃.

Step 1: Understand the reactants and products

When hydrogen gas (\( \text{H}_2 \)) reacts with other elements such as oxygen, chlorine, and nitrogen, they form different compounds. The key is to identify the possible products: with oxygen, water (\( \text{H}_2\text{O} \)); with chlorine, hydrogen chloride (\( \text{HCl} \)); and with nitrogen, ammonia (\( \text{NH}_3 \)).

Step 2: Write the unbalanced equations

Start by writing the basic form of the chemical reactions. For oxygen: \( \text{H}_2 + \text{O}_2 \rightarrow \text{H}_2\text{O} \). For chlorine: \( \text{H}_2 + \text{Cl}_2 \rightarrow \text{HCl} \). For nitrogen: \( \text{H}_2 + \text{N}_2 \rightarrow \text{NH}_3 \). These are the skeleton equations that need to be balanced.

Step 3: Balance the reaction with oxygen

In the equation \( \text{H}_2 + \text{O}_2 \rightarrow \text{H}_2\text{O} \), balance the number of oxygen atoms first. Since each side should have an even number of atoms, multiply \( \text{H}_2\text{O} \) by 2: \( \text{H}_2 + \frac{1}{2}\text{O}_2 \rightarrow 2\text{H}_2\text{O} \). Balance the hydrogen by making it: \( 2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O} \).

Step 4: Balance the reaction with chlorine

In \( \text{H}_2 + \text{Cl}_2 \rightarrow \text{HCl} \), each molecule of \( \text{Cl}_2 \) produces two molecules of \( \text{HCl} \). Balance it as: \( \text{H}_2 + \text{Cl}_2 \rightarrow 2\text{HCl} \).

Step 5: Balance the reaction with nitrogen

In the reaction \( \text{H}_2 + \text{N}_2 \rightarrow \text{NH}_3 \), adjust to balance nitrogen first: \( \text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3 \). This ensures that each side of the equation has the same number of nitrogen and hydrogen atoms.

Key Concepts

Chemical Reactions

Chemical reactions involve the transformation of one set of chemical substances into another. This process is fundamental in chemistry and forms the basis for understanding how different substances interact. During a chemical reaction, the substances present at the start, called reactants, undergo chemical changes to form new substances, known as products.
One example of a chemical reaction is when hydrogen gas (\( \text{H}_2 \)) reacts with oxygen gas (\( \text{O}_2 \)). This reaction forms water (\( \text{H}_2\text{O} \)), a compound made of hydrogen and oxygen. Similarly, hydrogen gas can react with chlorine to form hydrogen chloride (\( \text{HCl} \)), or with nitrogen to produce ammonia (\( \text{NH}_3 \)).
Chemical reactions can be represented by balanced chemical equations. These equations show the reactants and products involved, as well as their respective quantities, and must obey the law of conservation of mass. This law states that matter cannot be created or destroyed in a chemical reaction, so the mass of the products must equal the mass of the reactants.

Hydrogen Reactions

Hydrogen is a highly reactive element known for its ability to form bonds with many other elements. This reactivity arises from its single electron, which it can easily share or exchange during bonding. When hydrogen reacts with other elements, it often forms simple molecules.

• In the presence of oxygen, hydrogen combusts to produce water. This exothermic reaction releases energy, making hydrogen a potential clean fuel option.
• When combined with chlorine gas, hydrogen forms hydrogen chloride. This synthesis reaction is typically rapid and can be dangerous due to its high reactivity.
• Hydrogen's reaction with nitrogen, yielding ammonia, is a crucial industrial process known as the Haber process. Ammonia is vital for fertilizers, playing a significant role in agriculture.

Understanding these reactions requires awareness of the conditions under which hydrogen changes states or forms different compounds. Each reaction embodies distinct characteristics, such as energy released or absorbed, which are essential in both practical applications and theoretical chemistry.

Stoichiometry

Stoichiometry is a branch of chemistry that deals with the quantitative aspects of chemical reactions. It involves calculating the amounts of reactants and products in a reaction, ensuring that the equation complies with the law of conservation of mass.

Balancing chemical equations is a vital part of stoichiometry. It ensures that every atom involved in a reaction is accounted for on both sides of the equation. For example, balancing the equation for hydrogen reacting with oxygen: \[2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}.\]By balancing, we maintain that the number of hydrogen and oxygen atoms remains constant, with four hydrogen atoms and two oxygen atoms on each side.

Stoichiometry also involves mole ratios, which are derived from the coefficients of a balanced equation. These ratios allow quantitative predictions of the amounts of products formed from given reactants. In our hydrogen and nitrogen reaction:\[\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3.\]This tells us that one mole of nitrogen reacts with three moles of hydrogen to produce two moles of ammonia.

By mastering stoichiometry, chemists can predict reaction yields and design processes that maximize efficiency, minimize waste, and contribute to cost-effective chemical manufacturing.