Question

Balance the following chemical equations. Classify the reactions as decomposition, combination, singledisplacement, double-displacement, or combustion. (a) \(\mathrm{CaCl}_{2}(a q)+\mathrm{Na}_{2} \mathrm{SO}_{4}(a q) \longrightarrow\) \(\mathrm{CaSO}_{4}(s)+\mathrm{NaCl}(a q)\) (b) \(\mathrm{Ba}(s)+\mathrm{HCl}(a q) \longrightarrow \mathrm{BaCl}_{2}(a q)+\mathrm{H}_{2}(g)\) (c) \(\mathrm{N}_{2}(g)+\mathrm{H}_{2}(g) \longrightarrow \mathrm{NH}_{3}(g)\) (d) \(\mathrm{FeO}(s)+\mathrm{CO}(g) \stackrel{\text { heat }}{\longrightarrow} \mathrm{Fe}(s)+\mathrm{CO}_{2}(g)\) (e) \(\mathrm{CaO}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(a q)\) (f) \(\mathrm{Na}_{2} \mathrm{CrO}_{4}(a q)+\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(a q)\) \(\mathrm{PbCrO}_{4}(s)+\mathrm{NaNO}_{3}(a q)\) (g) \(\mathrm{KI}(a q)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{KCl}(a q)+\mathrm{I}_{2}(a q)\) (h) \(\mathrm{NaHCO}_{3}(s) \stackrel{\text { heul }}{\longrightarrow} \mathrm{Na}_{2} \mathrm{CO}_{3}(s)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)\)

Short answer

The balanced equations and their classifications are: (a) CaCl2(aq) + Na2SO4(aq) -> CaSO4(s) + 2NaCl(aq) - Double-displacement;(b) Ba(s) + 2HCl(aq) -> BaCl2(aq) + H2(g) - Single-displacement;(c) N2(g) + 3H2(g) -> 2NH3(g) - Combination;(d) FeO(s) + CO(g) -> Fe(s) + CO2(g) - Double-displacement;(e) CaO(s) + H2O(l) -> Ca(OH)2(aq) - Combination;(f) Na2CrO4(aq) + Pb(NO3)2(aq) -> PbCrO4(s) + 2NaNO3(aq) - Double-displacement;(g) 2KI(aq) + Cl2(g) -> 2KCl(aq) + I2(aq) - Single-displacement;(h) 2NaHCO3(s) -> Na2CO3(s) + CO2(g) + H2O(g) - Decomposition.

Step-by-step solution

Balancing and Classifying Equations (a) - (h)

There are multiple equations to balance and classify, each will be dealt with individually. (a) CaCl2(aq) + Na2SO4(aq) -> CaSO4(s) + 2NaCl(aq) - This is a double-displacement reaction.(b) Ba(s) + 2HCl(aq) -> BaCl2(aq) + H2(g) - This is a single-displacement reaction.(c) N2(g) + 3H2(g) -> 2NH3(g) - This is a combination reaction.(d) FeO(s) + CO(g) -> Fe(s) + CO2(g) - This is a double-displacement reaction.(e) CaO(s) + H2O(l) -> Ca(OH)2(aq) - This is a combination reaction.(f) Na2CrO4(aq) + Pb(NO3)2(aq) -> PbCrO4(s) + 2NaNO3(aq) - This is a double-displacement reaction.(g) 2KI(aq) + Cl2(g) -> 2KCl(aq) + I2(aq) - This is a single-displacement reaction.(h) 2NaHCO3(s) -> Na2CO3(s) + CO2(g) + H2O(g) - This is a decomposition reaction.

Key concepts

Balancing Chemical Equations

When we talk about balancing chemical equations, our goal is to make sure the number of each type of atom is the same on both sides of the equation. In other words, mass is conserved in the reaction, reflecting the law of conservation of mass.

To balance a chemical equation, follow these steps:

• Begin by writing down the unbalanced equation.
• List all the elements and count the number of atoms for each element present in both reactants and products.
• Start by balancing the elements that appear in only one reactant and one product first, moving on to more complex elements last.
• Add coefficients to the molecules as necessary to achieve balance. Remember, coefficients must be the smallest set of integers possible.

For example, take the equation for the formation of ammonia:\[\text{Unbalanced: } \mathrm{N}_{2}(g) + \mathrm{H}_{2}(g) \rightarrow \mathrm{NH}_{3}(g)\]We start by balancing the nitrogen atoms, then hydrogen:\[\mathrm{N}_{2}(g) + 3\mathrm{H}_{2}(g) \rightarrow 2\mathrm{NH}_{3}(g)\]By balancing, this equation now has two nitrogen and six hydrogen atoms on both sides.

Reaction Classification

Understanding the classification of chemical reactions is key to predicting the products that come from a reaction and understanding its behavior.

There are several main categories of chemical reactions:

• Combination Reactions: Two or more reactants combine to form a single product. An example is the reaction \[\mathrm{N}_{2}(g) + 3\mathrm{H}_{2}(g) \rightarrow 2\mathrm{NH}_{3}(g)\]. Here, nitrogen and hydrogen gases combine to form ammonia.
• Decomposition Reactions: A single reactant breaks down into multiple products. Consider the reaction \[2\mathrm{NaHCO}_{3}(s) \rightarrow \mathrm{Na}_{2}\mathrm{CO}_{3}(s) + \mathrm{CO}_{2}(g) + \mathrm{H}_{2}\mathrm{O}(g)\].
• Single-Displacement Reactions: An atom in a compound is replaced by an atom of a different element. For instance, \[\mathrm{Ba}(s) + 2\mathrm{HCl}(aq) \rightarrow \mathrm{BaCl}_{2}(aq) + \mathrm{H}_{2}(g)\].
• Double-Displacement Reactions: The ions of two compounds exchange places in an aqueous solution to form two new compounds. The reaction between calcium chloride and sodium sulfate is an example: \[\mathrm{CaCl}_{2}(aq) + \mathrm{Na}_{2}\mathrm{SO}_{4}(aq) \rightarrow \mathrm{CaSO}_{4}(s) + 2\mathrm{NaCl}(aq)\].
• Combustion Reactions: These involve a substance combining with oxygen, releasing energy in the form of light and heat.

Types of Chemical Reactions

Recognizing the types of chemical reactions can assist in understanding the chemical changes occurring in a laboratory or in nature. These types are based on the outcomes and the specific changes occurring during the reaction.

• Combination Reactions: As these involve the merger of different substances to form one complex product, they are essential in areas like chemical synthesis and metabolism in cells.
• Decomposition Reactions: These are crucial in processes such as digestion and the breakdown of organic matter.
• Single-Displacement Reactions: Often seen in metallurgy and thermite reactions where iron is displaced by aluminum.
• Double-Displacement Reactions: Seen extensively in the formation of precipitates and in real-life applications like the purification of materials.
• Combustion Reactions: These reactions are central to engines and power plants, where fuels burn to release energy.

Chemical reactions can also include special cases, like redox reactions, where oxidation and reduction occur together. Understanding these special reactions can offer insights into additional complex scenarios beyond typical classifications.