Question

Give the balanced equation for each of the following. a, The combustion of ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{OH}\right)\) 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 \(\mathrm{HCl}\) to form aqueous zinc chloride and hydrogen gas. d. Aqueous strontium hydroxide reacts with aqueous hydrobromic acid to produce water and aqueous strontium bromide.

Short answer

a. \(C_{2}H_{5}OH + 3O_{2} \rightarrow 2CO_{2} + 3H_{2}O\) b. \(2Pb(NO_{3})_{2(aq)} + 3Na_{3}PO_{4(aq)} \rightarrow Pb_{3}(PO_{4})_{2(s)} + 6NaNO_{3(aq)}\) c. \(Zn(s) + 2HCl(aq) \rightarrow ZnCl_{2(aq)} + H_{2(g)}\) d. \(Sr(OH)_{2(aq)} + 2HBr(aq) \rightarrow 2H_{2}O(l) + SrBr_{2(aq)}\)

Step-by-step solution

a. Combustion of Ethanol

The combustion of ethanol (C2H5OH) involves its reaction with oxygen gas (O2), producing carbon dioxide (CO2) and water vapor (H2O). Write the unbalanced equation first and then balance the equation. Unbalanced equation: C2H5OH + O2 → CO2 + H2O Balanced equation: \(C_{2}H_{5}OH + 3O_{2} \rightarrow 2CO_{2} + 3H_{2}O\)

b. Precipitate Formation in Aqueous Solution

Aqueous solutions of lead(II) nitrate (Pb(NO3)2) and sodium phosphate (Na3PO4) are mixed, resulting in the precipitate formation of lead(II) phosphate (Pb3(PO4)2) and aqueous sodium nitrate (NaNO3) as the other product. Write the unbalanced equation and then balance it. Unbalanced equation: Pb(NO3)2 + Na3PO4 → Pb3(PO4)2 + NaNO3 Balanced equation: \(2Pb(NO_{3})_{2(aq)} + 3Na_{3}PO_{4(aq)} \rightarrow Pb_{3}(PO_{4})_{2(s)} + 6NaNO_{3(aq)}\)

c. Solid Zinc Reaction

Solid zinc (Zn) reacts with aqueous HCl (hydrochloric acid) to form aqueous zinc chloride (ZnCl2) and hydrogen gas (H2). Write the unbalanced equation and then balance the equation. Unbalanced equation: Zn + HCl → ZnCl2 + H2 Balanced equation: \(Zn(s) + 2HCl(aq) \rightarrow ZnCl_{2(aq)} + H_{2(g)}\)

d. Aqueous Acid-Base Reaction

Aqueous strontium hydroxide (Sr(OH)2) reacts with aqueous hydrobromic acid (HBr) to produce water (H2O) and aqueous strontium bromide (SrBr2). Write the unbalanced equation and then balance the equation. Unbalanced equation: Sr(OH)2 + HBr → H2O + SrBr2 Balanced equation: \(Sr(OH)_{2(aq)} + 2HBr(aq) \rightarrow 2H_{2}O(l) + SrBr_{2(aq)}\)

Key concepts

Combustion of Ethanol

Ethanol, commonly found in alcoholic beverages and used as a biofuel, undergoes combustion when it reacts with oxygen in the air. This reaction releases energy, often in the form of heat and light, which is why burning ethanol can provide warmth or power engines.

The balanced chemical equation for ethanol combustion is:
\[C_{2}H_{5}OH + 3O_{2} \rightarrow 2CO_{2} + 3H_{2}O\]
In this equation, one ethanol molecule and three oxygen molecules react to form two carbon dioxide molecules and three water molecules. The conservation of mass is observed by ensuring the number of atoms for each element is equal on both sides of the equation. Understanding this concept is crucial in fields like environmental science and energy production, where the impact of combustion on air quality and the carbon cycle is of high concern.

Precipitate Formation

The process of precipitate formation is a hallmark of many chemical reactions, particularly in aqueous solutions. A precipitate is an insoluble solid that forms when two solutions containing soluble salts are combined, and a solid product is produced.

For example, mixing solutions of lead(II) nitrate and sodium phosphate leads to the formation of lead(II) phosphate, which is insoluble and precipitates out of solution. Here's how the balanced chemical equation looks:
\[2Pb(NO_{3})_{2(aq)} + 3Na_{3}PO_{4(aq)} \rightarrow Pb_{3}(PO_{4})_{2(s)} + 6NaNO_{3(aq)}\]
This reaction demonstrates the double replacement reaction, where ions in the reactant compounds exchange partners, resulting in the formation of at least one precipitate. Reactions like this are widely utilized in water treatment, medicine, and various industrial processes to isolate or remove certain compounds.

Balancing Chemical Equations

Balancing chemical equations is a fundamental skill in chemistry that ensures the law of conservation of mass is obeyed. This means that the number of each type of atom must be the same on both sides of the equation.

Throughout the examples provided in the exercise, from the combustion of ethanol to acid-base reactions, each balanced equation is carefully adjusted so that the amount of reactants equals the amount of products. Whether the reaction is simple or complex, the principles of balancing equations remain consistent: count the number of atoms of each element and add coefficients to balance the equation without altering the original compounds. For students, mastering this technique is essential as it forms the basis for understanding chemical reactions and stoichiometry.

Acid-Base Reaction

An acid-base reaction is a type of chemical reaction that involves the transfer of hydrogen ions between chemical species. They're among the most common reactions in chemistry, often resulting in the formation of water and a salt.

For instance, when aqueous strontium hydroxide, a base, reacts with hydrobromic acid, the reaction yields water and strontium bromide, a salt:
\[Sr(OH)_{2(aq)} + 2HBr(aq) \rightarrow 2H_{2}O(l) + SrBr_{2(aq)}\]
Understanding these reactions is critical in many areas, including biological systems, environmental chemistry, and industrial processes. Acid-base reactions are not only about pH changes but also encompass broader applications such as titration, which is used in laboratory settings to determine substance concentrations.