Question

Write balanced chemical equations to correspond 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, \(\mathrm{H}_{3} \mathrm{PO}_{3}(a q),\) 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

Here are the balanced chemical equations for the given reactions: (a) CaC2(s) + 2H2O(l) -> Ca(OH)2(aq) + C2H2(g) (b) 2KClO3(s) -> 2KCl(s) + 3O2(g) (c) Zn(s) + H2SO4(aq) -> H2(g) + ZnSO4(aq) (d) PCl3(l) + 3H2O(l) -> H3PO3(aq) + 3HCl(aq) (e) 3H2S(g) + 2Fe(OH)3(s) -> Fe2S3(s) + 6H2O(g)

Step-by-step solution

(a) Reaction between calcium carbide and water

Reactants: Solid calcium carbide (CaC2) and water (H2O) Products: Aqueous calcium hydroxide (Ca(OH)2) and acetylene gas (C2H2) Unbalanced equation: CaC2(s) + H2O(l) -> Ca(OH)2(aq) + C2H2(g) To balance the equation, we need 2 water molecules for every calcium carbide: Balanced equation: CaC2(s) + 2H2O(l) -> Ca(OH)2(aq) + C2H2(g)

(b) Decomposition of potassium chlorate

Reactants: Solid potassium chlorate (KClO3) Products: Solid potassium chloride (KCl) and oxygen gas (O2) Unbalanced equation: KClO3(s) -> KCl(s) + O2(g) To balance the equation, we need 2 potassium chlorate molecules for every 3 oxygen molecules: Balanced equation: 2KClO3(s) -> 2KCl(s) + 3O2(g)

(c) Reaction between zinc and sulfuric acid

Reactants: Solid zinc (Zn) and sulfuric acid (H2SO4) Products: Hydrogen gas (H2) and aqueous zinc sulfate (ZnSO4) Unbalanced equation: Zn(s) + H2SO4(aq) -> H2(g) + ZnSO4(aq) This equation is already balanced.

(d) Reaction between phosphorus trichloride and water

Reactants: Liquid phosphorus trichloride (PCl3) and water (H2O) Products: Aqueous phosphorous acid (H3PO3) and aqueous hydrochloric acid (HCl) Unbalanced equation: PCl3(l) + H2O(l) -> H3PO3(aq) + HCl(aq) To balance the equation, we need 3 hydrochloric acid molecules for every phosphorus trichloride molecule: Balanced equation: PCl3(l) + 3H2O(l) -> H3PO3(aq) + 3HCl(aq)

(e) Reaction between hydrogen sulfide and iron(III) hydroxide

Reactants: Hydrogen sulfide gas (H2S) and solid hot iron(III) hydroxide (Fe(OH)3) Products: Solid iron(III) sulfide (Fe2S3) and gaseous water (H2O) Unbalanced equation: H2S(g) + Fe(OH)3(s) -> Fe2S3(s) + H2O(g) To balance the equation, we need 3 hydrogen sulfide molecules and 2 iron(III) hydroxide molecules for every 2 iron(III) sulfide molecules and 6 water molecules: Balanced equation: 3H2S(g) + 2Fe(OH)3(s) -> Fe2S3(s) + 6H2O(g)

Key concepts

Balancing Equations

When dealing with chemical equations, balancing is a crucial step that ensures the law of conservation of mass is obeyed. This law states that mass cannot be created or destroyed in a chemical reaction. Therefore, the number of atoms of each element must be the same on both the reactant and product sides of the equation.

To balance a chemical equation, follow these steps:

• Write the unbalanced equation to get a clear picture of the reactants and the products involved.
• Count the number of atoms for each element in the reactants and the products.
• Adjust the coefficients (the numbers in front of the chemical formulas) to balance the atoms for each element on both sides.
• Repeat the process until you achieve a balanced equation.
• Re-check the equation to ensure all elements are balanced and that you have the simplest set of coefficients.

Balancing chemical equations requires patience and practice. Start with more complex compounds and leave simple substances like oxygen (O_2) or hydrogen (H_2) till the end. This approach can make balancing easier and more systematic.

Reactants and Products

In every chemical equation, we find two main parts: reactants and products. Understanding these terms is key to grasping chemical reactions.

• **Reactants** are the starting materials in a chemical reaction. They are usually found on the left side of the chemical equation. These substances undergo a chemical change as the reaction progresses.
• **Products** are the new substances formed as a result of the reaction. They appear on the right side of the equation and are different in composition due to the chemical transformation that took place.

For example, in the reaction where zinc reacts with sulfuric acid, the reactants are solid zinc (Zn) and sulfuric acid (H_2SO_4), whereas the products are hydrogen gas (H_2) and zinc sulfate (ZnSO_4).

The transition from reactants to products involves breaking of old bonds and formation of new ones, leading to the distinctive characteristics of the products compared to the initial reactants.

Decomposition Reactions

Decomposition reactions are a type of chemical reaction where a single compound breaks down into two or more simpler substances. This type of reaction is generally characterized by the formula:

A -> B + C

Several factors can cause decomposition, including heat, light, or electricity. These reactions are important in numerous industries and scientific studies. They often require energy input to proceed.

An example of decomposition reaction is the decomposition of potassium chlorate (KClO_3) when heated. The balanced chemical equation for this process would be:

2KClO_3(s) -> 2KCl(s) + 3O_2(g)

Here, solid potassium chlorate decomposes into solid potassium chloride (KCl) and gaseous oxygen (O_2). Notice how the number and type of atoms remain consistent before and after the reaction, in line with the law of conservation of mass. By understanding decomposition reactions, you can identify and predict the products of certain chemical processes.