Question

following reactions could be followed: (a) \(\mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaO}(s)+\mathrm{CO}_{2}(g)\) (b) \(\mathrm{Cl}_{2}(g)+2 \mathrm{Br}^{-}(a q) \longrightarrow \mathrm{Br}_{2}(a q)+2 \mathrm{Cl}^{-}(a q)\) (c) \(\mathrm{C}_{2} \mathrm{H}_{6}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2}(g)\) (d) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(a q)+\mathrm{H}^{+}(a q)+\mathrm{I}^{-}(a q)\)

Short answer

(a) Decomposition, (b) Redox, (c) Decomposition, (d) Substitution.

Step-by-step solution

Identify the Type of Reaction

Examine each reaction to determine whether it is a decomposition, redox, or substitution reaction.(a) The reaction \( \mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaO}(s)+\mathrm{CO}_{2}(g) \) is a decomposition reaction because \( \mathrm{CaCO}_{3} \) breaks down into \( \mathrm{CaO} \) and \( \mathrm{CO}_{2} \).(b) The reaction \( \mathrm{Cl}_{2}(g)+2 \mathrm{Br}^{-}(a q) \longrightarrow \mathrm{Br}_{2}(a q)+2 \mathrm{Cl}^{-}(a q) \) is a redox reaction since there is a transfer of electrons between chlorine and bromide ions.(c) The reaction \( \mathrm{C}_{2} \mathrm{H}_{6}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2}(g) \) is a decomposition reaction, as \( \mathrm{C}_{2} \mathrm{H}_{6} \) breaks down to form \( \mathrm{C}_{2} \mathrm{H}_{4} \) and \( \mathrm{H}_{2} \).(d) The reaction \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(a q)+\mathrm{H}^{+}(a q)+\mathrm{I}^{-}(a q) \) is a substitution reaction. The iodine atom in \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I} \) is replaced by an \( \mathrm{OH} \) group.

Balance the Reactions

Verify that each reaction is balanced in terms of mass and charge.(a) \( \mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaO}(s)+\mathrm{CO}_{2}(g) \) is already balanced with one \( \mathrm{Ca} \), one \( \mathrm{C} \), and three \( \mathrm{O} \) atoms on each side.(b) \( \mathrm{Cl}_{2}(g)+2 \mathrm{Br}^{-}(a q) \longrightarrow \mathrm{Br}_{2}(a q)+2 \mathrm{Cl}^{-}(a q) \) is balanced as it has two chlorines and two bromides on each side.(c) \( \mathrm{C}_{2} \mathrm{H}_{6}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2}(g) \) is balanced with two carbons and six hydrogens on both sides.(d) \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(a q)+\mathrm{H}^{+}(a q)+\mathrm{I}^{-}(a q) \) is balanced with all atoms accounted for, with balance of charge as \( \mathrm{H}^{+} \) and \( \mathrm{I}^{-} \) ions are formed.

Key concepts

Decomposition Reaction

A decomposition reaction is when a single compound breaks down into two or more simpler substances. This type of reaction is all about breaking things apart. It often involves the breaking of chemical bonds, and it can be caused by heating, light, or electricity.
A classic example is observed in reactions like \[\mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaO}(s) + \mathrm{CO}_{2}(g)\]In this process, one compound, calcium carbonate \(\mathrm{CaCO}_{3}\), is split into calcium oxide \(\mathrm{CaO}\) and carbon dioxide \(\mathrm{CO}_{2}\).
Decomposition reactions are fundamental as they help understand how compounds can transform when their environments change.

• They are usually endothermic, meaning they absorb energy.
• Common applications include digestion, where large molecules are broken into simpler molecules in our bodies.

Redox Reaction

Redox reactions are fascinating because they involve the transfer of electrons between two substances. The term "redox" is a combination of "reduction" and "oxidation," which happen together in these reactions.
For instance: \[\mathrm{Cl}_{2}(g) + 2 \mathrm{Br}^{-}(a q) \longrightarrow \mathrm{Br}_{2}(a q) + 2 \mathrm{Cl}^{-}(a q)\]In this reaction, chlorine is reduced, gaining electrons, while bromide is oxidized, losing electrons.
This coupled process of reduction and oxidation is crucial in the chemistry world.

• Redox reactions are essential in batteries, where electron transfer powers your devices.
• They are responsible for processes like rusting and combustion.

Substitution Reaction

Substitution reactions occur when one atom or group of atoms in a molecule is replaced with a different atom or group. They're like a chemical swap, changing parts of compounds.
A prime example is: \[\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I}(g) + \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(a q) + \mathrm{H}^{+}(a q) + \mathrm{I}^{-}(a q)\]Here, iodine \(\mathrm{I}\) is substituted by a hydroxyl group \(\mathrm{OH}\), forming ethanol and hydronium ions.
These reactions are key in creating new substances.

• Substitution reactions are predominant in organic chemistry for synthesizing new compounds.
• Common everyday examples include the reaction of halogens with alkanes.

Balanced Chemical Equations

Balanced chemical equations ensure that atoms are neither created nor destroyed. Balancing is crucial because it follows the Law of Conservation of Mass, which states the mass of reactants must equal the mass of products.
Consider: \[\mathrm{Cl}_{2}(g) + 2 \mathrm{Br}^{-}(a q) \longrightarrow \mathrm{Br}_{2}(a q) + 2 \mathrm{Cl}^{-}(a q)\]In this redox equation, the number of chlorine and bromine atoms are the same on both sides, showing balance.
Balancing helps in understanding how much of each reactant is needed or how much of a product will form.

• It ensures that chemical equations reflect reality.
• Balanced equations are essential for quantitative chemical analysis calculations.