Question

Complete and balance the equations for the following reactions, and identify the type of reaction that each equation represents. a. \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{S}(a q)+\mathrm{ZnCl}_{2}(a q) \longrightarrow\) _____ \(+\mathrm{ZnS}(s)\) b. \(\operatorname{Al}(s)+\operatorname{Pb}\left(\mathrm{NO}_{3}\right)_{2}(a q) \longrightarrow\) _____ c. \(\mathrm{Ba}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) _____ d. \(\mathrm{Cl}_{2}(g)+\mathrm{KBr}(a q) \longrightarrow\) _____ e. \(\mathrm{NH}_{3}(g)+\mathrm{O}_{2}(g) \stackrel{\mathrm{Pt}}{\longrightarrow} \mathrm{NO}(g)+\mathrm{H}_{2} \mathrm{O}(l)\) f. \(\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g)\)

Short answer

a. (\mathrm{NH}_{4}){}_{2} \mathrm{S} + \mathrm{ZnCl}_{2} \rightarrow 2\mathrm{NH}_{4}Cl + \mathrm{ZnS} (Double Displacement) b. 2 \mathrm{Al} + 3 \mathrm{Pb}(\mathrm{NO}_{3})_{2} \rightarrow 2\mathrm{Al}(\mathrm{NO}_{3})_{3} + 3\mathrm{Pb} (Single Displacement) c. \mathrm{Ba} + 2\mathrm{H}_{2}O \rightarrow \mathrm{Ba(OH)_{2}} + \mathrm{H}_{2} (Single Displacement) d. \mathrm{Cl}_{2} + 2\mathrm{KBr} \rightarrow 2\mathrm{KCl} + \mathrm{Br}_{2} (Single Displacement) e. 4\mathrm{NH}_{3} + 5\mathrm{O}_{2} \stackrel{\mathrm{Pt}}{\rightarrow} 4\mathrm{NO} + 6\mathrm{H}_{2}\mathrm{O} (Combustion) f. 2\mathrm{H}_{2}O \rightarrow 2\mathrm{H}_{2} + \mathrm{O}_{2} (Decomposition)

Step-by-step solution

Title - Balance equation (a)

1. Write the reactants and products: \[(\mathrm{NH}_{4}){}_{2} \mathrm{S}(aq) + \mathrm{ZnCl}_{2}(aq) \rightarrow \mathrm{NH}_{4}Cl(aq) + \mathrm{ZnS}(s)\]2. Balance nitrogen, hydrogen, chlorine, sulfur, and zinc atoms: \[(\mathrm{NH}_{4}){}_{2} \mathrm{S}(aq) + \mathrm{ZnCl}_{2}(aq) \rightarrow 2\mathrm{NH}_{4}Cl(aq) + \mathrm{ZnS}(s)\]This reaction is a double displacement reaction.

Title - Balance equation (b)

1. Write the reactants and products:\[\mathrm{Al}(s) + \mathrm{Pb}(\mathrm{NO}_{3})_{2}(aq) \rightarrow \mathrm{Al}(\mathrm{NO}_{3})_{3}(aq) + \mathrm{Pb}(s)\]2. Balance aluminum, lead and nitrate ions:\[2 \mathrm{Al}(s) + 3 \mathrm{Pb}(\mathrm{NO}_{3})_{2}(aq) \rightarrow 2 \mathrm{Al}(\mathrm{NO}_{3})_{3}(aq) + 3 \mathrm{Pb}(s)\]This reaction is a single displacement reaction.

Title - Balance equation (c)

1. Write the reactants and products:\[\mathrm{Ba}(s) + \mathrm{H}_{2}O(l) \rightarrow \mathrm{Ba(OH)_{2}}(aq) + \mathrm{H}_{2}(g)\]2. Balance barium, hydrogen, and oxygen atoms:\[\mathrm{Ba}(s) + 2\mathrm{H}_{2}O(l) \rightarrow \mathrm{Ba(OH)_{2}}(aq) + \mathrm{H}_{2}(g)\]This reaction is a single displacement reaction.

Title - Balance equation (d)

1. Write the reactants and products:\[\mathrm{Cl}_{2}(g) + \mathrm{KBr}(aq) \rightarrow \mathrm{KCl}(aq) + \mathrm{Br}_{2}(aq)\]2. Balance chlorine, potassium, and bromine atoms:\[\mathrm{Cl}_{2}(g) + 2\mathrm{KBr}(aq) \rightarrow 2\mathrm{KCl}(aq) + \mathrm{Br}_{2}(aq)\]This reaction is a single displacement reaction.

Title - Balance equation (e)

1. Write the reactants and products:\[4\mathrm{NH}_{3}(g) + 5\mathrm{O}_{2}(g) \stackrel{\mathrm{Pt}}{\rightarrow} 4\mathrm{NO(g)} + 6\mathrm{H}_{2}O(l)\]2. Ensure all atoms are balanced:\[4\mathrm{NH}_{3}(g) + 5\mathrm{O}_{2}(g) \stackrel{\mathrm{Pt}}{\rightarrow} 4\mathrm{NO(g)} + 6\mathrm{H}_{2}O(l)\]This reaction is a combustion reaction.

Title - Balance equation (f)

1. Write the reactants and products:\[2\mathrm{H}_{2}O(l) \rightarrow 2 \mathrm{H}_{2}(g) + \mathrm{O}_{2}(g)\]2. Ensure all atoms are balanced:\[2\mathrm{H}_{2}O(l) \rightarrow 2 \mathrm{H}_{2}(g) + \mathrm{O}_{2}(g)\]This reaction is a decomposition reaction.

Key concepts

double displacement reaction

A double displacement reaction is a type of chemical reaction where two compounds exchange ions to form two new compounds.
These reactions generally occur in aqueous solutions because the compounds need to be dissociated into ions.
A perfect example is given in the exercise: \[(\mathrm{NH}_{4}){}_{2} \mathrm{S}(aq) + \mathrm{ZnCl}_{2}(aq) \rightarrow 2\mathrm{NH}_{4}Cl(aq) + \mathrm{ZnS}(s)\]
Here, the ammonium sulfide and zinc chloride swap ions, resulting in ammonium chloride and zinc sulfide.

• This type of reaction is also known as a metathesis reaction.
• Examples often involve salt solutions that form a precipitate, gas, or water.

This reaction is balanced by ensuring the number of each type of atom on both sides of the equation is equal.

single displacement reaction

A single displacement reaction involves one element being displaced from a compound by another element.
This type of reaction usually occurs when a more reactive element replaces a less reactive element in a compound.
For instance, consider the reaction in the exercise: \[(\mathrm{Al}(s) + \mathrm{Pb}(\mathrm{NO}_{3})_{2}(aq) \rightarrow \mathrm{Al}(\mathrm{NO}_{3})_{3}(aq) + \mathrm{Pb}(s))\] In this scenario:

• Aluminum displaces lead from lead nitrate.
• Another example could be: \[(\mathrm{Cl}_{2}(g) + 2\mathrm{KBr}(aq) \rightarrow 2\mathrm{KCl}(aq) + \mathrm{Br}_{2}(aq))\] where chlorine displaces bromine from potassium bromide.

These reactions typically occur in solutions where elements can dissociate easily.
The equation must be balanced, meaning the number of atoms for each element should be the same on both sides.

combustion reaction

A combustion reaction is a chemical reaction where a substance combines with oxygen, releasing energy in the form of light and heat.
These reactions are a type of exothermic reaction, meaning they release energy during the process.
An example from the exercise is: \[(4\mathrm{NH}_{3}(g) + 5\mathrm{O}_{2}(g) \stackrel{\mathrm{Pt}}{\rightarrow} 4\mathrm{NO(g)} + 6\mathrm{H}_{2}O(l))\]
In this reaction, ammonia reacts with oxygen, producing nitrogen monoxide and water.

• Commonly seen in burning fuels like hydrocarbons.
• Combustion requires a fuel (usually a hydrocarbon), oxygen, and a spark or ignition source.

Balancing combustion reactions involves ensuring all elements on the reactant side match the products.

decomposition reaction

A decomposition reaction is a type of chemical reaction where one compound breaks down into two or more simpler substances.
This breakdown is often the result of heating, a catalyst, or an electric current.
Take the example from the exercise: \[(2\mathrm{H}_{2}O(l) \rightarrow 2\mathrm{H}_{2}(g) + \mathrm{O}_{2}(g))\]
In this reaction, water decomposes into hydrogen and oxygen gas.

• Decomposition reactions are essential in industrial processes such as the electrolysis of water.
• They often require external energy input.

This equation is balanced by ensuring the number of each atom type on both sides of the equation is equal.