Problem 84 - Chemistry Matter and Change

Question

Write a balanced chemical equation for the combustion of liquid methanol \(\left(\mathrm{CH}_{3} \mathrm{OH}\right)\).

Step-by-Step Solution

Answer

The balanced chemical equation for the combustion of liquid methanol is: \( 2 \textrm{CH}_{3}\textrm{OH} (l) + 3 \textrm{O}_{2} (g) \rightarrow 2 \textrm{CO}_{2} (g) + 4 \textrm{H}_{2}\textrm{O} (l) \)

Step 1: Write the unbalanced chemical equation

To write the unbalanced equation, let's begin with the reactants, liquid methanol (CH3OH) and oxygen gas (O2), and the products of combustion which are carbon dioxide (CO2) and water (H2O): CH3OH (l) + O2 (g) → CO2 (g) + H2O (l)

Step 2: Balance the carbon atoms

We will start by balancing carbon atoms. There is 1 carbon atom in methanol and 1 carbon atom in carbon dioxide, so the carbon atoms are already balanced: CH3OH (l) + O2 (g) → CO2 (g) + H2O (l)

Step 3: Balance the hydrogen atoms

Next, we balance the hydrogen atoms. There are 4 hydrogen atoms in methanol and only 2 hydrogen atoms in water. Therefore, we need to multiply the water by 2 to balance the hydrogen atoms: CH3OH (l) + O2 (g) → CO2 (g) + 2 H2O (l) Now, the hydrogen atoms are balanced, as there are 4 hydrogen atoms on both sides of the equation.

Step 4: Balance the oxygen atoms

Lastly, we need to balance the oxygen atoms. There are 3 oxygen atoms in the reactants (1 in methanol and 2 in oxygen gas) and 4 oxygen atoms in the products (2 in carbon dioxide and 2 in the two water molecules). To balance the oxygen atoms, we will multiply the oxygen gas by 1.5: CH3OH (l) + 1.5 O2 (g) → CO2 (g) + 2 H2O (l) However, we should avoid using fractions in a balanced chemical equation. Thus, to remove the fraction, we will multiply the entire equation by 2 to obtain whole numbers: 2 CH3OH (l) + 3 O2 (g) → 2 CO2 (g) + 4 H2O (l)

Step 5: Check the balanced equation

Finally, let's verify that the equation is balanced: - 2 carbon atoms in the reactants (2 CH3OH) and 2 carbon atoms in the products (2 CO2) - 8 hydrogen atoms in the reactants (2 CH3OH) and 8 hydrogen atoms in the products (4 H2O) - 6 oxygen atoms in the reactants (3 O2) and 6 oxygen atoms in the products (2 CO2 + 4 H2O) Since we have an equal number of atoms for each element on both sides of the equation, we conclude that the balanced chemical equation for the combustion of liquid methanol is: 2 CH3OH (l) + 3 O2 (g) → 2 CO2 (g) + 4 H2O (l)

Key Concepts

Combustion Reaction

A combustion reaction is a type of chemical reaction where a substance combines with oxygen to release heat and light, often in the form of a flame. In simple terms, it's the burning process. Combustion typically results in the formation of carbon dioxide, water, and heat.
For example, when we burn wood or gasoline, combustion reactions are taking place.
In our exercise, methanol undergoes combustion in the presence of oxygen to produce carbon dioxide and water.

• The general form of a combustion reaction is: a hydrocarbon + oxygen → carbon dioxide + water
• They are exothermic, meaning they release energy.

Understanding combustion reactions is crucial for various applications, including generating power and understanding environmental impacts.

Methanol

Methanol, also known as wood alcohol, is the simplest form of alcohol and is represented by the chemical formula \(\mathrm{CH}_{3} \mathrm{OH}\). It is a light, volatile, colorless liquid with a distinctive alcoholic odor. Methanol is not suitable for drinking due to its toxicity, but it has many industrial uses.

• Used as a solvent, antifreeze, and fuel.
• It burns efficiently in combustion reactions.

In the context of our chemical equation, methanol serves as the fuel that reacts with oxygen in the air to produce energy, carbon dioxide, and water. Understanding methanol's role in chemical reactions helps in fields like energy production and environmental science.

Stoichiometry

Stoichiometry is the area of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It's like the recipe behind a chemical reaction, ensuring that everything is measured accurately.
By using stoichiometry, we can determine the right amount of each reactant to use and predict how much product will be formed. This is important for efficiently carrying out reactions with minimal waste.

• Involves balancing chemical equations.
• Ensures that the law of conservation of mass is adhered to.

In the balanced equation for the combustion of methanol, applying stoichiometry helps us know exactly how much oxygen is needed for a given amount of methanol to ensure the reactants are completely used.

Chemical Reactions

A chemical reaction involves the transformation of one or more substances into new products. During this process, the chemical structure of the substances changes, resulting in new substances with different properties.
Chemical reactions are fundamental to everyday processes, from digestion to rusting iron. They can be classified into types, such as combustion, synthesis, decomposition, and more.

• Reactants are the starting substances in a reaction.
• Products are the substances formed as a result of the reaction.
• Signs of a chemical reaction include gas production, color change, heat, and the formation of precipitates.

Recognizing chemical reactions helps us understand the natural world and harness these changes for practical applications.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions, showing the starting materials and the resulting products. They serve as the "recipe" for reactions, much like instructions, making it easy to understand what happens during a reaction.
In a chemical equation:

• Reactants are written on the left side.
• Products on the right side.
• An arrow separates the reactants from the products, indicating the direction of the reaction.

Balancing chemical equations is essential as it ensures that we respect the law of conservation of mass; this means that each element has the same number of atoms on both sides of the equation. In our methanol combustion exercise, balancing was crucial to ensure accurate representation, with the final balanced equation showing the proper proportions needed for the reaction to occur without leftovers.