Problem 22 - Chemistry: The Central Science in SI Units, Global Edition

Question

Balance the following equations and indicate whether they are combination, decomposition, or combustion reactions: (a) \(\mathrm{NaClO}_{3}(s) \longrightarrow \mathrm{NaCl}(s)+\mathrm{O}_{2}(g)\) (b) \(\mathrm{NH}_{4} \mathrm{OH}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{NH}_{3}(g)\) (c) \(\mathrm{K}(s)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{KCl}(s)\) (d) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(l)\)

Step-by-Step Solution

Answer

(a) Balanced Equation: \( \mathrm{2 NaClO}_{3}(s) \longrightarrow \mathrm{2 NaCl}(s)+\frac{3}{2}\mathrm{O}_{2}(g) \), Decomposition Reaction (b) Balanced Equation: \( \mathrm{NH}_{4} \mathrm{OH}(a q) \longrightarrow \mathrm{H}_{2}\mathrm{O}(l)+\mathrm{NH}_{3}(g) \), Decomposition Reaction (c) Balanced Equation: \( \mathrm{2K}(s)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{2KCl}(s) \), Combination Reaction (d) Balanced Equation: \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l)+\mathrm{3 O}_{2}(g) \longrightarrow \mathrm{2 CO}_{2}(\mathrm{~g})+\mathrm{3 H}_{2} \mathrm{O}(l) \), Combustion Reaction

Step 1: (a) Identify the type of reaction

In this reaction, a single compound, NaClO3, breaks down into two products, NaCl and O2. So, it is a decomposition reaction.

Step 2: (a) Balance the equation

Balancing the decomposition reaction: NaClO3(s) -> NaCl(s) + O2(g) We can balance the oxygen atoms by multiplying the O2 by 1.5: \[ \mathrm{2 NaClO}_{3}(s) \longrightarrow \mathrm{2 NaCl}(s)+\frac{3}{2}\mathrm{O}_{2}(g) \]

Step 3: (b) Identify the type of reaction

In this reaction, a single compound, NH4OH, breaks down into two products, H2O and NH3. So, it is a decomposition reaction.

Step 4: (b) Balance the equation

Balancing the decomposition reaction: NH4OH(aq) -> H2O(l) + NH3(g) This equation is already balanced.

Step 5: (c) Identify the type of reaction

In this reaction, two reactants (K and Cl2) are combining to form a single product (KCl). So, it is a combination reaction.

Step 6: (c) Balance the equation

Balancing the combination reaction: K(s) + Cl2(g) -> KCl(s) We can balance the chlorine atoms by multiplying KCl by 2: \[ \mathrm{2K}(s)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{2KCl}(s) \]

Step 7: (d) Identify the type of reaction

In this reaction, a hydrocarbon, C2H5OH, reacts with O2, and the products are CO2 and H2O. This is a combustion reaction.

Step 8: (d) Balance the equation

Balancing the combustion reaction: C2H5OH(l) + O2(g) -> CO2(g) + H2O(l) There are 2 carbon atoms, 6 hydrogen atoms, and 3 oxygen atoms on reactants side. There is 1 carbon atom, 2 hydrogen atoms, and 3 oxygen atoms on products side. So, we can balance by placing coefficients as follows: \[ \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l)+\mathrm{3 O}_{2}(g) \longrightarrow \mathrm{2 CO}_{2}(\mathrm{~g})+\mathrm{3 H}_{2} \mathrm{O}(l) \]

Key Concepts

Decomposition Reaction

A decomposition reaction occurs when one compound breaks down into two or more simpler substances. This process is a crucial aspect of chemistry and is quite commonly encountered. These reactions can be initiated by heat, light, or electricity. For example, let's consider the decomposition of sodium chlorate (\(\text{NaClO}_3\)):

• In the equation \(\text{NaClO}_3(s) \longrightarrow \text{NaCl}(s)+\text{O}_2(g)\), sodium chlorate decomposes into sodium chloride and oxygen gas.
• Since a single compound breaks into two different substances, it fits the definition of a decomposition reaction.
• To balance this reaction, ensure the number of atoms of each element is equal on both sides of the equation.

For example, balancing the reaction requires adjusting coefficients: \[ \text{2 NaClO}_3(s) \longrightarrow \text{2 NaCl}(s) + \frac{3}{2}\text{O}_2(g) \]Understanding decomposition reactions is important because they can describe many natural and industrial processes, such as the breakdown of chemicals in plants or wastewater treatment.

Combination Reaction

Combination reactions involve two or more reactants coming together to form a single product. This process is also sometimes referred to as a synthesis reaction. It marks the simplest formation of chemical reactions, where elements form compounds. A classic example can be seen in the synthesis of potassium chloride (\(\text{KCl}\)):

• The reaction \(\text{K}(s)+\text{Cl}_2(g) \longrightarrow \text{KCl}(s)\), combines the elements potassium and chlorine to produce potassium chloride.
• This reaction reflects the principle that when elements combine to form a compound, the mass and elements must be conserved.
• Balancing the equation involves ensuring equal numbers of each type of atom on both sides.

For instance, to balance this equation, change the coefficients: \[ \text{2K}(s)+\text{Cl}_2(g) \longrightarrow \text{2KCl}(s) \]Combination reactions are significant because they demonstrate elemental interactions forming complex structures, relating to things like the rusting of iron or formation of water from hydrogen and oxygen.

Combustion Reaction

Combustion reactions are vigorous chemical reactions usually involving the presence of oxygen and characterized by the production of heat and light, in the form of a flame. These reactions are essential in various energy-producing processes.A typical example of combustion is the reaction of ethanol (\(\text{C}_2\text{H}_5\text{OH}\)):

• The equation \(\text{C}_2\text{H}_5\text{OH}(l)+\text{O}_2(g) \longrightarrow \text{CO}_2(g)+\text{H}_2\text{O}(l)\), demonstrates the burning of ethanol in the presence of oxygen.
• This process involves the conversion of a hydrocarbon and oxygen into carbon dioxide and water.
• Balancing a combustion reaction typically requires making sure that the number of carbon, hydrogen, and oxygen atoms are equal on both sides.

Consider balancing this particular reaction as follows: \[ \text{C}_2\text{H}_5\text{OH}(l)+\text{3O}_2(g) \longrightarrow \text{2CO}_2(g)+\text{3H}_2\text{O}(l) \]Combustion reactions are fundamentally important, not only for understanding biochemical processes but also for analyzing energy utilization and production in everyday life, such as in vehicles and power plants.