Problem 96 - Chemistry An Atoms First Approach

Question

Give the balanced equation for each of the following. a. The combustion of ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) forms carbon dioxide and water vapor. A combustion reaction refers to a reaction of a substance with oxygen gas. b. Aqueous solutions of lead(II) nitrate and sodium phosphate are mixed, resulting in the precipitate formation of lead(II) phosphate with aqueous sodium nitrate as the other product. c. Solid zinc reacts with aqueous HCl to form aqueous zinc chloride and hydrogen gas. d. Aqueous strontium hydroxide reacts with aqueous hydrobromic acid to produce water and aqueous strontium bromide.

Step-by-Step Solution

Answer

a. \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} + 3 \mathrm{O}_{2} \rightarrow 2 \mathrm{CO}_{2} + 3 \mathrm{H}_{2}\mathrm{O}\) b. \(3 \mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2} + 2 \mathrm{Na}_{3}\mathrm{PO}_{4} \rightarrow \mathrm{Pb}_{3}\left(\mathrm{PO}_{4}\right)_{2} + 6 \mathrm{NaNO}_{3}\) c. \(\mathrm{Zn} + 2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2} + \mathrm{H}_{2}\) d. \(\mathrm{Sr}\left(\mathrm{OH}\right)_{2} + 2 \mathrm{HBr} \rightarrow 2 \mathrm{H}_{2}\mathrm{O} + \mathrm{SrBr}_{2}\)

Step 1: a. Combustion of ethanol

Write down the unbalanced equation of combustion of ethanol reacting with oxygen gas to form carbon dioxide and water vapor. The unbalanced equation is: \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} + \mathrm{O}_{2} \rightarrow \mathrm{CO}_{2} + \mathrm{H}_{2}\mathrm{O}\) Now, balance the equation by adjusting the coefficients: \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} + 3 \mathrm{O}_{2} \rightarrow 2 \mathrm{CO}_{2} + 3 \mathrm{H}_{2}\mathrm{O}\)

Step 2: b. Reaction of lead(II) nitrate and sodium phosphate

Write down the unbalanced equation of aqueous solutions of lead(II) nitrate and sodium phosphate reacting to form lead(II) phosphate precipitate and aqueous sodium nitrate. The unbalanced equation is: \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2} + \mathrm{Na}_{3}\mathrm{PO}_{4} \rightarrow \mathrm{Pb}_{3}\left(\mathrm{PO}_{4}\right)_{2} + \mathrm{NaNO}_{3}\) Now, balance the equation by adjusting the coefficients: \(3 \mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2} + 2 \mathrm{Na}_{3}\mathrm{PO}_{4} \rightarrow \mathrm{Pb}_{3}\left(\mathrm{PO}_{4}\right)_{2} + 6 \mathrm{NaNO}_{3}\)

Step 3: c. Reaction of solid zinc with aqueous HCl

Write down the unbalanced equation of solid zinc reacting with aqueous HCl to form aqueous zinc chloride and hydrogen gas. The unbalanced equation is: \(\mathrm{Zn} + \mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2} + \mathrm{H}_{2}\) Now, balance the equation by adjusting the coefficients: \(\mathrm{Zn} + 2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2} + \mathrm{H}_{2}\)

Step 4: d. Reaction of aqueous strontium hydroxide with aqueous hydrobromic acid

Write down the unbalanced equation of aqueous strontium hydroxide reacting with aqueous hydrobromic acid to produce water and aqueous strontium bromide. The unbalanced equation is: \(\mathrm{Sr}\left(\mathrm{OH}\right)_{2} + \mathrm{HBr} \rightarrow \mathrm{H}_{2}\mathrm{O} + \mathrm{SrBr}_{2}\) Now, balance the equation by adjusting the coefficients: \(\mathrm{Sr}\left(\mathrm{OH}\right)_{2} + 2 \mathrm{HBr} \rightarrow 2 \mathrm{H}_{2}\mathrm{O} + \mathrm{SrBr}_{2}\)

Key Concepts

Combustion Reactions

Combustion reactions are fascinating and crucial processes that typically involve a substance reacting with oxygen to release energy. This energy is often in the form of heat and light. A classic example of a combustion reaction is the burning of ethanol \((\text{C}_2\text{H}_5\text{OH})\). In this reaction, ethanol combines with oxygen \((\text{O}_2)\) from the air to produce carbon dioxide \((\text{CO}_2)\) and water \((\text{H}_2\text{O})\). The balanced chemical equation for this reaction can be written as: \[ \text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O} \]Balancing combustion reactions requires ensuring equal numbers of each type of atom on both sides of the equation. Here's a quick tip: start by balancing the elements that appear in the fewest compounds first and save oxygen for last, as it often appears in multiple reactants or products. This strategy simplifies balancing these dynamic reactions.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions combine to form an insoluble solid known as a precipitate. This type of reaction often involves the exchange of ions between the reacting solutions. In the case of lead(II) nitrate \((\text{Pb}(\text{NO}_3)_2)\) and sodium phosphate \((\text{Na}_3\text{PO}_4)\) solutions, a solid precipitate of lead(II) phosphate \((\text{Pb}_3(\text{PO}_4)_2)\) forms. The balanced equation for this reaction is:\[ 3 \text{Pb}(\text{NO}_3)_2 + 2 \text{Na}_3\text{PO}_4 \rightarrow \text{Pb}_3(\text{PO}_4)_2 + 6 \text{NaNO}_3 \]The key to understanding precipitation reactions is recognizing which combinations of ions will form insoluble compounds. Solubility rules can help predict if a precipitate will form, providing a clear guide to these reactions. Remember that when ions form a precipitate, it removes them from the solution phase, driving the reaction forward.

Acid-Base Reactions

Acid-base reactions are essential processes where an acid reacts with a base to produce water and a salt. One classic example of this is the reaction between strontium hydroxide \((\text{Sr(OH)}_2)\) and hydrobromic acid \((\text{HBr})\). When these compounds interact, they transform into water \((\text{H}_2\text{O})\) and strontium bromide \((\text{SrBr}_2)\), as shown in the balanced equation:\[ \text{Sr(OH)}_2 + 2 \text{HBr} \rightarrow 2 \text{H}_2\text{O} + \text{SrBr}_2 \]This reaction is a typical example of a neutralization reaction, where the acid \(\text{HBr}\) donates protons to the hydroxide ions \((\text{OH}^-\)) from the base, forming water. The remaining ions form a salt, in this case, strontium bromide. Understanding these reactions involves recognizing the role of acids and bases in donating and accepting protons, respectively, and how they form water and salts as a result.

Stoichiometry

Stoichiometry is a fundamental concept in chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It allows us to predict the amounts of substances consumed and produced by using balanced chemical equations. For the reaction of zinc with hydrochloric acid:\[ \text{Zn} + 2 \text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \]Stoichiometry tells us that one mole of zinc reacts with two moles of hydrochloric acid to produce one mole of zinc chloride and one mole of hydrogen gas. The balanced equation provides the necessary mole ratios required to perform calculations involving masses, volumes, or even determining limiting reactants. To effectively use stoichiometry, always ensure that the chemical equation is balanced, which ensures the conservation of mass and correct corresponding quantities of substances involved in the reaction.