Question

Methane, \(\mathrm{CH}_{4}(g),\) burns in oxygen, \(\mathrm{O}_{2}(g),\) to produce carbon dioxide, \(\mathrm{CO}_{2}(g),\) and water, \(\mathrm{H}_{2} \mathrm{O}(l) .\) a. Write a balanced equation for this process. b. This process is described as irreversible. What does this mean?

Short answer

a. \(\text{CH}_4(g) + 2 \text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)\); b. Irreversible reactions proceed to completion and do not reverse under normal conditions.

Step-by-step solution

Identify Reactants and Products

The reactants for the combustion of methane are methane \(\text{CH}_4\) and oxygen \(\text{O}_2\). The products formed are carbon dioxide \(\text{CO}_2\) and water \(\text{H}_2\text{O}\).

Write the Unbalanced Equation

Start by writing the unbalanced chemical equation using chemical symbols: \[\text{CH}_4(g) + \text{O}_2(g) \rightarrow \text{CO}_2(g) + \text{H}_2\text{O}(l)\]

Balance the Equation

Balance the number of atoms for each element on both sides of the equation. Begin by balancing the carbons, hydrogens, and then oxygens. The balanced equation is: \[\text{CH}_4(g) + 2 \text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)\]

Explain Irreversibility

In chemical terms, an irreversible reaction is one in which the reactants convert to products and do not easily convert back to reactants. The combustion of methane is irreversible as it proceeds to completion, with methane and oxygen fully reacting to form carbon dioxide and water, and under normal conditions, the reverse reaction does not occur.

Key concepts

Chemical Equation Balancing

Chemical equation balancing is a vital part of understanding chemical reactions. Imagine it like a seesaw where each side must have the same weight. In chemistry, instead of weight, we balance the number of atoms. When methane \(\mathrm{CH}_4\) is burned, it reacts with oxygen \(\mathrm{O}_2\).To balance the equation, we write down all reactants and products, ensuring each element appears on both sides with equal atom numbers:

• Start by balancing the carbon atoms. Methane contains one carbon atom, which should balance with one carbon atom in carbon dioxide \(\mathrm{CO}_2\).
• Next, balance the hydrogens. Methane has four hydrogen atoms. So, you need two water molecules \(\mathrm{H}_2\mathrm{O}\), providing the four hydrogen atoms needed.
• Finally, balance the oxygens. With one \(\mathrm{CO}_2\) and two \(\mathrm{H}_2\mathrm{O}\) molecules, you need four oxygen atoms in total, so two \(\mathrm{O}_2\) molecules are required.

Balancing ensures the Law of Conservation of Mass is followed, meaning matter is neither created nor destroyed. This results in the balanced equation: \[\text{CH}_4(g) + 2 \text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)\] Using systematic steps makes balancing manageable and precise.

Irreversible Reactions

Irreversible reactions are a fascinating concept where reactions proceed in one direction only. Once the reactants convert into products, they don't revert back under normal conditions. It's like baking a cake; once baked, you can't easily turn it back into the original batter. In the case of the combustion of methane, once methane and oxygen form carbon dioxide and water, they remain as these products:

• The process is highly exothermic, releasing energy in the form of heat, causing the products to be more thermodynamically stable than the reactants.
• Additionally, the high stability of the final products prevents them from spontaneously converting back to the original reactants.

Thus, this directionality and the difficulty of the reverse reaction under typical conditions characterize the irreversibility of a reaction. Understanding irreversible reactions is essential for recognizing why some chemical processes reach completion.

Reactants and Products

In any chemical reaction, understanding the role of reactants and products is crucial. Let's think of them as inputs and outputs in a recipe.

• **Reactants** are the starting materials. In our case, methane \(\mathrm{CH}_4\) and oxygen \(\mathrm{O}_2\) are the key reactants.
• **Products** are the substances formed as a result of the reaction. For combustion, the products are carbon dioxide \(\mathrm{CO}_2\) and water \(\mathrm{H}_2\mathrm{O}\).

Chemical reactions involve these reactants undergoing transformations under specific conditions:This knowledge allows chemists to design and predict the outcomes of reactions effectively. By clearly identifying and understanding both reactants and products, one can strategize about how best to achieve the desired reaction outcome.

Stoichiometry

Stoichiometry is like the mathematical backbone of chemistry, giving us the calculations needed to quantify relationships in a chemical reaction. It describes the ratio in which materials react and the quantities produced.By examining the balanced chemical equation:\[\text{CH}_4(g) + 2 \text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)\] we gather:

• Every mole of methane reacts with two moles of oxygen.
• This reaction produces one mole of carbon dioxide and two moles of water.

This stoichiometric ratio is used to determine the exact amounts of reactants needed to obtain a desired quantity of products.Suppose a chemist needs two moles of carbon dioxide. Stoichiometry tells them they'll need precisely two moles of methane and four moles of oxygen. These calculations are invaluable in labs and industries, optimizing resource use and ensuring reactions are economically viable.