Problem 13 - Chemistry: Atoms First

Question

Indicate what type, or types, of reaction each of the following represents: (a) \(\mathrm{Ca}(s)+\mathrm{Br}_{2}(l) \longrightarrow \mathrm{CaBr}_{2}(s)\) (b) \(\mathrm{Ca}(\mathrm{OH})_{2}(a q)+2 \mathrm{HBr}(a q) \rightarrow \mathrm{CaBr}_{2}(a q)+2 \mathrm{H}_{2} \mathrm{O}(l)\) (c) \(\mathrm{C}_{6} \mathrm{H}_{12}(l)+9 \mathrm{O}_{2}(g) \longrightarrow 6 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(g)\)

Step-by-Step Solution

Answer

The reaction (a) is a synthesis reaction, (b) is a neutralization reaction, and (c) is a combustion reaction.

Step 1: Identify Reaction Type for (a)

Inspect the reactants and products for (a). The reaction starts with calcium, a metal, reacting with bromine, a diatomic non-metal, to produce calcium bromide, an ionic compound. This is a synthesis or combination reaction because two or more substances combine to form a single product.

Step 2: Identify Reaction Type for (b)

Examine the reactants and products for (b). This is an acid-base reaction, specifically, it is a neutralization reaction where an acid (HBr) and a base (Ca(OH)2) react to produce a salt (CaBr2) and water.

Step 3: Identify Reaction Type for (c)

Analyze the reactants and products for (c). This is a combustion reaction, identified by a hydrocarbon (C6H12) reacting with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O), releasing energy in the form of heat and/or light.

Key Concepts

Synthesis Reaction

Imagine stacking building blocks to create something new; that's akin to a synthesis reaction in chemistry. In essence, a synthesis reaction, also known as a combination reaction, occurs when two or more simple substances combine to form a more complex substance. The general form of a synthesis reaction is \( A + B \rightarrow AB \).

For example, when calcium (Ca), a metal, reacts with bromine (Br₂), which is a diatomic non-metal, the result is calcium bromide (CaBr₂), an ionic compound. This transformation from simpler substances to a compound is a hallmark of a synthesis reaction. Synthesis reactions are fundamental to the creation of many compounds in chemistry and are pivotal in various industrial and manufacturing processes.

Real-World Example of Synthesis Reaction

One real-world example is the formation of table salt, where sodium (Na) reacts with chlorine (Cl₂) to form sodium chloride (NaCl). This simple synthesis reaction is essential for producing one of the most common seasonings found in kitchens worldwide.

Neutralization Reaction

Think of a neutralization reaction as a dance between an acid and a base, with the two partners coming together to reach a state of balance or 'neutrality.' A neutralization reaction occurs when an acid and a base react to form water and a salt. pH plays a large role in this type of reaction, as the interaction between the acid and the base typically results in a pH closer to 7, which is neutral on the pH scale.

In the reaction where calcium hydroxide (Ca(OH)₂), a base, and hydrobromic acid (HBr), an acid, come together, they produce calcium bromide (CaBr₂), a salt, and water (H₂O). The equation \( Ca(OH)_2 + 2HBr \rightarrow CaBr_2 + 2H_2O \) provides a clear demonstration of this process.

Importance in Everyday Life

Neutralization reactions are crucial in many everyday processes, from treating upset stomachs with antacids (which neutralize excess stomach acid) to managing the acidity of soil in agriculture.

Combustion Reaction

A combustion reaction is akin to a firework exploding in the sky — it can be fast, ferocious, and releases energy. This type of reaction occurs when a fuel (usually a hydrocarbon) reacts with an oxidant (typically oxygen) to produce carbon dioxide, water, and energy in the form of heat or light. The basic equation for a combustion reaction is \( C_xH_y + O_2 \rightarrow CO_2 + H_2O \).

For instance, when the hydrocarbon C₆H₁₂ reacts with oxygen (O₂), this combustion reaction produces carbon dioxide (CO₂) and water (H₂O), releasing energy. This type of reaction is what powers our vehicles, heats our homes, and even cooks our food.

Energy and Environment

Combustion reactions are a significant source of energy for modern society but also pose environmental challenges due to carbon emissions. Consequently, understanding combustion is not only key for energy production but also for developing cleaner and more sustainable practices.