Problem 19 - Chemistry The Central Science

Question

Write a balanced chemical equation for the reaction that occurs when (a) \(\mathrm{Mg}(s)\) reacts with \(\mathrm{Cl}_{2}(g) ;\) (b) barium carbonate decomposes into barium oxide and carbon dioxide gas when heated; (c) the hydrocarbon styrene, \(\mathrm{C}_{8} \mathrm{H}_{8}(l),\) is combusted in air; (d) dimethylether, \(\mathrm{CH}_{3} \mathrm{OCH}_{3}(g),\) is combusted in air.

Step-by-Step Solution

Answer

a) \(Mg(s) + Cl_{2}(g) \rightarrow MgCl_{2}(s)\) b) \(BaCO_{3}(s) \rightarrow BaO(s) + CO_{2}(g)\) c) \(C_{8}H_{8}(l) + 6O_{2}(g) \rightarrow 8CO_{2}(g) + 4H_{2}O(l)\) d) \(CH_{3}OCH_{3}(g) + 3O_{2}(g) \rightarrow 2CO_{2}(g) + 3H_{2}O(l)\)

Step 1: Reaction a: Magnesium reacting with chlorine gas

When magnesium reacts with chlorine gas, it forms magnesium chloride. The balanced chemical equation for this reaction is: \[Mg(s) + Cl_{2}(g) \rightarrow MgCl_{2}(s)\]

Step 2: Reaction b: Decomposition of barium carbonate

When barium carbonate decomposes, it forms barium oxide and carbon dioxide gas. The balanced chemical equation for this reaction is: \[BaCO_{3}(s) \rightarrow BaO(s) + CO_{2}(g)\]

Step 3: Reaction c: Combustion of styrene

Combustion of the hydrocarbon styrene (\(C_{8}H_{8}(l)\)) in air produces carbon dioxide and water. The balanced chemical equation for this reaction is: \[C_{8}H_{8}(l) + 6O_{2}(g) \rightarrow 8CO_{2}(g) + 4H_{2}O(l)\]

Step 4: Reaction d: Combustion of dimethyl ether

Combustion of dimethyl ether (\(CH_{3}OCH_{3}(g)\)) in air produces carbon dioxide and water. The balanced chemical equation for this reaction is: \[CH_{3}OCH_{3}(g) + 3O_{2}(g) \rightarrow 2CO_{2}(g) + 3H_{2}O(l)\]

Key Concepts

Reaction Types

In chemistry, reactions are categorized based on how the reactants transform into products. Recognizing reaction types can simplify predicting products and balancing equations. Here are some common types of reactions:

• Synthesis (or combination) reactions: Two or more reactants unite to form a single product.
• Decomposition reactions: A single compound breaks down into two or more simpler substances.
• Combustion reactions: A hydrocarbon reacts with oxygen, releasing energy, carbon dioxide, and water.
• Single-replacement reactions: One element switches places with another in a compound.
• Double-replacement reactions: Components of two compounds swap places to form two new compounds.

Understanding these types helps in anticipating the outcomes of chemical reactions. This is especially useful in complex scenarios such as organic chemistry.

Chemical Reaction Balancing

Balancing chemical equations ensures that the same number of each type of atom is present on both sides of the equation. This is crucial for obeying the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a chemical reaction. Here is a simple approach to balance equations:

• List each type of atom involved in the reactants and products.
• Count the number of atoms of each element on both sides.
• Add coefficients to balance the number of atoms for each element. Start with the most complex molecule.
• Ensure the coefficients are in the simplest ratio. Typically, whole numbers are used.

The balanced equation provides the stoichiometric relationship between the reactants and products, allowing for precise calculations in chemistry.

Combustion Reactions

Combustion reactions involve the burning of substances in the presence of oxygen. These reactions are exothermic, meaning they release heat. Hydrocarbons are common fuels burned in these types of reactions. The general formula for the combustion of a hydrocarbon is:
\[ C_xH_y + O_2 ightarrow CO_2 + H_2O \]
For complete combustion, enough oxygen is present to completely oxidize the hydrocarbon to carbon dioxide and water. Partial combustion, however, may produce carbon monoxide or other products if insufficient oxygen is available. Practical applications of combustion include fuel for engines and energy production. Combustion also plays a vital role in daily life, from heating homes to generating electricity.

Decomposition Reactions

Decomposition reactions involve breaking down a compound into simpler substances, typically triggered by heat, light, or electricity. They are the opposite of synthesis reactions. A general decomposition reaction can be represented as:
\[ AB ightarrow A + B \]
Decomposition can occur in simple or complex compounds. Thermal decomposition, for example, involves heat breaking chemical bonds, as seen in the heating of barium carbonate yielding barium oxide and carbon dioxide. Not only does decomposition provide essential industrial applications, such as in the production of lime (CaO) from limestone (CaCO₃), but it also has biological importance, evident when living organisms decompose organic matter, recycling nutrients in ecosystems.