Problem 106 - General Chemistry

Question

Classify each of the following reactions as a combination reaction, decomposition reaction, displacement reaction, or combustion reaction. a. When solid calcium oxide, \(\mathrm{CaO}\), is exposed to gaseous sulfur trioxide, \(\mathrm{SO}_{3}\), solid calcium sulfate, \(\mathrm{CaSO}_{4}\), is formed. b. Calcium metal (solid) reacts with water to produce a solution of calcium hydroxide, \(\mathrm{Ca}(\mathrm{OH})_{2}\), and hydrogen gas. c. When solid sodium hydrogen sulfite, \(\mathrm{NaHSO}_{3}\), is heated, solid sodium sulfite, \(\mathrm{Na}_{2} \mathrm{SO}_{3}\), sulfur dioxide gas, \(\mathrm{SO}_{2}\), and water vapor are formed. d. Magnesium reacts with bromine to give magnesium bromide, \(\mathrm{MgBr}_{2}\).

Step-by-Step Solution

Answer

a) Combination, b) Displacement, c) Decomposition, d) Combination.

Step 1: Understand Reaction Types

There are four primary types of chemical reactions: combination reactions (two or more substances combine to form a single product), decomposition reactions (a single substance breaks down into two or more substances), displacement reactions (an element reacts with a compound, replacing one of its components), and combustion reactions (a substance reacts with oxygen to produce energy and often carbon dioxide and water).

Step 2: Analyze Reaction a

The reaction of solid calcium oxide (\(\mathrm{CaO}\)) with gaseous sulfur trioxide (\(\mathrm{SO}_3\)) to form solid calcium sulfate (\(\mathrm{CaSO}_4\)) can be written as: \[ \mathrm{CaO}(s) + \mathrm{SO}_3(g) \rightarrow \mathrm{CaSO}_4(s) \]. This is a combination reaction since two reactants combine to form one product.

Step 3: Analyze Reaction b

Calcium metal (\(\mathrm{Ca}\)) reacting with water (\(\mathrm{H}_2\mathrm{O}\)) produces calcium hydroxide (\(\mathrm{Ca(OH)}_2\)) and hydrogen gas (\(\mathrm{H}_2\)). The equation is: \[ \mathrm{Ca}(s) + 2\mathrm{H}_2\mathrm{O}(l) \rightarrow \mathrm{Ca(OH)}_2(aq) + \mathrm{H}_2(g) \]. This is a displacement reaction as calcium displaces hydrogen in water.

Step 4: Analyze Reaction c

Heating solid sodium hydrogen sulfite (\(\mathrm{NaHSO}_3\)) results in the formation of sodium sulfite (\(\mathrm{Na}_2\mathrm{SO}_3\)), sulfur dioxide (\(\mathrm{SO}_2\)), and water vapor. The equation is: \[ 2\mathrm{NaHSO}_3(s) \rightarrow \mathrm{Na}_2\mathrm{SO}_3(s) + \mathrm{SO}_2(g) + \mathrm{H}_2\mathrm{O}(g) \]. This is a decomposition reaction because a single compound breaks down into multiple products.

Step 5: Analyze Reaction d

The reaction of magnesium (\(\mathrm{Mg}\)) with bromine (\(\mathrm{Br}_2\)) to form magnesium bromide (\(\mathrm{MgBr}_2\)) is: \[ \mathrm{Mg}(s) + \mathrm{Br}_2(l) \rightarrow \mathrm{MgBr}_2(s) \]. This is a combination reaction as the two elements combine to form a single product.

Key Concepts

Combination Reactions

Combination reactions occur when two or more substances merge to form a single, new product. This type of reaction is also known as a synthesis reaction.
In these reactions, the reactants are typically elements or simpler compounds. During the process, they bond together to create a more complex compound.
For example, the reaction between solid calcium oxide (\(\mathrm{CaO}\)) and gaseous sulfur trioxide (\(\mathrm{SO}_3\)) to produce solid calcium sulfate (\(\mathrm{CaSO}_4\)) is a classic combination reaction:

• Equation: \( \mathrm{CaO}(s) + \mathrm{SO}_3(g) \rightarrow \mathrm{CaSO}_4(s) \)
• Both reactants merge to form one single product, \(\mathrm{CaSO}_4\).

Combination reactions are important in various fields such as material science, enabling the creation of new substances with unique properties.

Decomposition Reactions

Decomposition reactions involve a single compound breaking down into two or more simpler products. These reactions are the reverse of combination reactions.
They require energy input, usually in the form of heat, light, or electricity, to break the bonds in the original compound.
An example can be seen when heating sodium hydrogen sulfite (\(\mathrm{NaHSO}_3\)), which decomposes into sodium sulfite (\(\mathrm{Na}_2\mathrm{SO}_3\)), sulfur dioxide (\(\mathrm{SO}_2\)), and water vapor:

• Equation: \( 2\mathrm{NaHSO}_3(s) \rightarrow \mathrm{Na}_2\mathrm{SO}_3(s) + \mathrm{SO}_2(g) + \mathrm{H}_2\mathrm{O}(g) \)
• The single compound \(\mathrm{NaHSO}_3\) breaks down into three separate products.

Decomposition reactions are common in processes like metal extraction and waste treatment.

Displacement Reactions

Displacement reactions occur when an element reacts with a compound, displacing another element from it. There are two main types: single-displacement and double-displacement reactions.
In single-displacement reactions, an element replaces a less reactive element in a compound. This is evident in the reaction of calcium with water, where calcium displaces hydrogen:

• Equation: \( \mathrm{Ca}(s) + 2\mathrm{H}_2\mathrm{O}(l) \rightarrow \mathrm{Ca(OH)}_2(aq) + \mathrm{H}_2(g) \)
• Calcium replaces hydrogen, forming calcium hydroxide and hydrogen gas.

Displacement reactions are essential in metallurgy for extracting metals and in many biological processes.

Combustion Reactions

Combustion reactions are not explicitly detailed in the given document, but understanding them is crucial.
These reactions involve substances reacting with oxygen, often producing heat, and are typically exothermic. One common product of combustion reactions is carbon dioxide, especially when organic compounds burn.
A general equation for a simple combustion reaction involving a hydrocarbon would be:

• Equation: \( \mathrm{C}_x\mathrm{H}_y + \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + \mathrm{H}_2\mathrm{O} \)
• The reactant combines with \(\mathrm{O}_2\), releasing energy and forming \(\mathrm{CO}_2\) and water.

Combustion is a central concept in energy production, such as in engines and power plants.