Problem 81 - Chemistry: The Central Science

Question

Write the balanced chemical equatiuns fur (a) the complete combustion of acetic acid \(\left(\mathrm{CH}_{3} \mathrm{COOH}\right)\), the main active ingredient in vinegar; (b) the decomposition of solid calcium hydroxide into solid calcium(II) oxide (lime) and water vapor; (c) the combination reaction between nickel metal and chlorine gas.

Step-by-Step Solution

Answer

The balanced chemical equations for each reaction are: a) Complete combustion of acetic acid: \(2 \mathrm{CH}_{3}\mathrm{COOH}+O_{2} \rightarrow 2 \mathrm{CO}_{2}+2 \mathrm{H}_{2} \mathrm{O}\) b) Decomposition of solid calcium hydroxide: \(\mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{CaO}+\mathrm{H}_{2} \mathrm{O}\) c) Combination reaction between nickel metal and chlorine gas: \(\mathrm{Ni}+2 \mathrm{Cl}_{2} \rightarrow \mathrm{NiCl}_{2}\)

Step 1: Determine the products for each reaction.

Before we balance the equations, we need to identify the products of each reaction: a) Complete combustion reactions involve the reaction of a compound with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O). b) Decomposition reactions involve a single compound breaking down into two or more simpler substances. c) Combination reactions involve two or more substances joining to form a single compound.

Step 2: Write the unbalanced chemical equations.

Next, we write the unbalanced equations for each reaction, based on our knowledge of the reactants and products: a) CH3COOH + O2 → CO2 + H2O b) Ca(OH)2 → CaO + H2O c) Ni + Cl2 → NiCl2

Step 3: Balance the chemical equations.

Now, we balance each equation by adjusting the coefficients (the numbers in front of each compound) to ensure that the number of each element is equal on both sides: a) Combustion of acetic acid: - We need 2 carbon atoms and 4 hydrogen atoms on both sides. - The balanced equation becomes: \(2 \mathrm{CH}_{3}\mathrm{COOH}+O_{2} \rightarrow 2 \mathrm{CO}_{2}+2 \mathrm{H}_{2} \mathrm{O}\) b) Decomposition of calcium hydroxide: - The equation is already balanced: \(\mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{CaO}+\mathrm{H}_{2} \mathrm{O}\) c) Combination of nickel and chlorine: - We need 2 chlorine atoms on both sides. - The balanced equation becomes: \(\mathrm{Ni}+2 \mathrm{Cl}_{2} \rightarrow \mathrm{NiCl}_{2}\)

Step 4: Summary of balanced chemical equations

The balanced chemical equations for each reaction are as follows: a) Complete combustion of acetic acid: \(2 \mathrm{CH}_{3}\mathrm{COOH}+O_{2} \rightarrow 2 \mathrm{CO}_{2}+2 \mathrm{H}_{2} \mathrm{O}\) b) Decomposition of solid calcium hydroxide: \(\mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{CaO}+\mathrm{H}_{2} \mathrm{O}\) c) Combination reaction between nickel metal and chlorine gas: \(\mathrm{Ni}+2 \mathrm{Cl}_{2} \rightarrow \mathrm{NiCl}_{2}\)

Key Concepts

Complete Combustion

Complete combustion refers to a type of chemical reaction where a compound, typically a hydrocarbon, reacts with an excess of oxygen to produce carbon dioxide, water, and energy. This reaction is commonly used in engines and power plants to generate heat and power. For instance, the combustion of acetic acid (CH_{3}COOH) in excess oxygen produces carbon dioxide and water, releasing heat in the process.
It is crucial that there is enough oxygen available for complete combustion to occur; otherwise, incomplete combustion may result, leading to the production of carbon monoxide and possibly soot. This could have harmful environmental and health impacts.

Decomposition Reaction

A decomposition reaction involves the breakdown of a compound into two or more simpler substances. Generally, this type of reaction requires an input of energy, such as heat, light, or electricity. For example, calcium hydroxide (Ca(OH)_2) decomposes into calcium oxide (lime) and water vapor when heated. This process is integral in various industries, including construction where lime is a key component in cement and mortar. Decomposition reactions are also important for recycling materials and understanding degradation processes in the environment.

Combination Reaction

Combination reactions, also known as synthesis reactions, occur when two or more reactants combine to form a single product. This fundamental type of chemical reaction is seen in various processes, from the formation of compounds in stars to the synthesis of molecules in living organisms. A classic example is the reaction between nickel metal and chlorine gas to form nickel(II) chloride. In combination reactions, the reactants may be elements or compounds and can vary from simple to very complex structures.

Balanced Chemical Equation

Writing a balanced chemical equation is an essential skill in chemistry as it ensures the law of conservation of mass is respected. To balance a chemical equation, the number of atoms for each element must be the same on both sides of the reaction. This is achieved by placing coefficients in front of the chemical formulas. A perfectly balanced equation allows one to accurately calculate the quantities required for a reaction and the expected yield. Additionally, it provides deeper insight into the stoichiometric relationships between reactants and products, which is pivotal in reaction stoichiometry.

Reactants and Products

In any given chemical reaction, substances that undergo the transformation are known as reactants, while substances that are generated by the reaction are called products. During a chemical reaction, the reactants are consumed to form the products, but the total mass and the number of atoms remain conserved. Understanding the reactants and products in a reaction simplifies the learning of chemical processes and assists in predicting the outcomes of reactions, which is crucial for applications across chemistry, biology, environmental science, and engineering.