Question

Write balanced chemical equations corresponding to each of the following descriptions: (a) Solid calcium carbide, ${\mathrm{CaC}}_2$, reacts with water to form an aqueous solution of calcium hydroxide and acetylene gas, ${\mathrm{C}}_2{\mathrm{H}}_2$. (b) When solid potassium chlorate is heated, it decomposes to form solid potassium chloride and oxygen gas. (c) Solid zinc metal reacts with sulfuric acid to form hydrogen gas and an aqueous solution of zinc sulfate. (d) When liquid phosphorus trichloride is added to water, it reacts to form aqueous phosphorous acid, ${\mathrm{H}}_3{\mathrm{PO}}_3(aq)$, and aqueous hydrochloric acid. (e) When hydrogen sulfide gas is passed over solid hot iron(III) hydroxide, the resultant reaction produces solid iron(III) sulfide and gaseous water.

Short answer

(a) CaC₂(s) + 2 H₂O(l) → Ca(OH)₂(aq) + C₂H₂(g) (b) 2 KClO₃(s) → 2 KCl(s) + 3 O₂(g) (c) Zn(s) + H₂SO₄(aq) → H₂(g) + ZnSO₄(aq) (d) PCl₃(l) + 3 H₂O(l) → H₃PO₃(aq) + 3 HCl(aq) (e) 6 H₂S(g) + 2 Fe(OH)₃(s) → Fe₂S₃(s) + 6 H₂O(g)

Step-by-step solution

(a) Balancing Calcium Carbide Reaction

In this reaction, solid calcium carbide (${\mathrm{CaC}}_2$) reacts with water to form an aqueous solution of calcium hydroxide and acetylene gas (${\mathrm{C}}_2{\mathrm{H}}_2$). We start by identifying the reactants and products: Reactants: ${\mathrm{CaC}}_2$ (solid) + H2O (liquid) Products: Calcium Hydroxide (aqueous) + ${\mathrm{C}}_2{\mathrm{H}}_2$ (gas) Now, we write the unbalanced chemical equation: CaC₂(s) + H2O(l) → Ca(OH)₂(aq) + C₂H₂(g) To balance the equation, add coefficients: CaC₂(s) + 2 H₂O(l) → Ca(OH)₂(aq) + C₂H₂(g)

(b) Balancing Potassium Chlorate Decomposition

In this reaction, solid potassium chlorate decomposes to form solid potassium chloride and oxygen gas: Reactants: KClO₃ (solid) Products: KCl (solid) + O₂ (gas) Write the unbalanced chemical equation: KClO₃(s) → KCl(s) + O₂(g) To balance the equation, add the coefficients: 2 KClO₃(s) → 2 KCl(s) + 3 O₂(g)

(c) Balancing Zinc Metal and Sulfuric Acid Reaction

In this reaction, solid zinc metal reacts with sulfuric acid to form hydrogen gas and an aqueous solution of zinc sulfate: Reactants: Zn(s) + H₂SO₄(aq) Products: H₂(g) + ZnSO₄(aq) Write the unbalanced chemical equation: Zn(s) + H₂SO₄(aq) → H₂(g) + ZnSO₄(aq) The equation is already balanced, so no further changes are needed.

(d) Balancing Phosphorus Trichloride Reaction

In this reaction, liquid phosphorus trichloride reacts with water to form aqueous phosphorous acid and aqueous hydrochloric acid: Reactants: PCl₃(l) + H₂O(l) Products: H₃PO₃(aq) + HCl(aq) Write the unbalanced chemical equation: PCl₃(l) + H₂O(l) → H₃PO₃(aq) + HCl(aq) To balance the equation, add coefficients: PCl₃(l) + 3 H₂O(l) → H₃PO₃(aq) + 3 HCl(aq)

(e) Balancing Hydrogen Sulfide and Iron(III) Hydroxide Reaction

In this reaction, hydrogen sulfide gas reacts with solid hot iron(III) hydroxide to form solid iron(III) sulfide and gaseous water: Reactants: H₂S(g) + Fe(OH)₃(s) Products: Fe₂S₃(s) + H₂O(g) Write the unbalanced chemical equation: H₂S(g) + Fe(OH)₃(s) → Fe₂S₃(s) + H₂O(g) To balance the equation, add coefficients: 6 H₂S(g) + 2 Fe(OH)₃(s) → Fe₂S₃(s) + 6 H₂O(g)

Key concepts

Chemical Reactions

Chemical reactions are processes where substances (reactants) transform into different substances (products). This change involves the breaking and forming of chemical bonds. Reactants are typically written on the left side, while products are on the right side of the chemical equation. The arrow between them indicates the direction of the transformation.

Understanding chemical reactions requires recognition of different types of reactions, such as synthesis, decomposition, and substitution reactions. For example, the decomposition reaction of potassium chlorate forming potassium chloride and oxygen showcases how a single compound breaks into simpler products.

These reactions often involve notable changes such as energy release or absorption, color changes, formation of precipitates, or the evolution of gases. Recognizing these signs can help one understand the nature and type of the chemical reaction taking place.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions. It's based on the conservation of mass, where the total mass of reactants equals the total mass of products. This principle is fundamental for quantitative chemical calculations.

Using stoichiometry, one can predict the amount of product formed from a given amount of reactant, as seen in our exercise. Each part of the chemical equation represents a mole ratio. By balancing equations, the stoichiometric coefficients provide these ratios, allowing us to calculate quantities accurately.

For instance, in the reaction of calcium carbide with water, stoichiometry helps in determining how much acetylene gas will form from a certain amount of calcium carbide. Thus, mastering stoichiometry is crucial for anyone wanting to delve deeper into chemical processes and their applications.

Chemical Equation Balancing

Balancing chemical equations is an essential skill in chemistry. It ensures that the same number of each type of atom appears on both sides of the equation, aligning with the law of conservation of mass.

The process begins by writing an unbalanced equation based on the reaction description. Then, adjust coefficients—whole numbers before formulas—to balance each type of atom in the equation. Balancing is done iteratively, often starting with the most complex molecule.

From our exercise, the added coefficients in equations like "2 KClO₃(s) → 2 KCl(s) + 3 O₂(g)" show how each reaction ensures atoms are conserved. Balancing equations helps in accurately predicting the quantities in reactions, aiding in practical applications and laboratory analyses.

Reactants and Products

Reactants and products are fundamental to understanding chemical reactions. Reactants are the starting substances that undergo change, while products are the new substances formed as a result.

Identifying reactants and products requires recognizing which substances are consumed and which are produced. In the reaction involving zinc and sulfuric acid, zinc and the acid are reactants, while hydrogen gas and zinc sulfate are products.

It's crucial to understand the state of reactants and products—whether solid, liquid, gas, or aqueous—as it influences reaction conditions and outcomes. This helps chemists design and optimize industrial processes or laboratory experiments. With practice, identifying reactants and products becomes second nature, enabling deeper insights into chemical phenomena.