Question

Write chemical equations to represent the following reactions. (a) Limestone rock (calcium carbonate) is heated (calcined) and decomposes to calcium oxide and carbon dioxide gas. (b) Zinc sulfide ore is heated in air (roasted) and is converted to zinc oxide and sulfur dioxide gas. (Note that oxygen gas in the air is also a reactant.) (c) Propane gas reacts with gaseous water to produce a mixture of carbon monoxide and hydrogen gases. (This mixture, called synthesis gas, is used to produce a variety of organic chemicals.) (d) Sulfur dioxide gas is passed into an aqueous solution containing sodium sulfide and sodium carbonate. The reaction products are carbon dioxide and an aqueous solution of sodium thiosulfate.

Short answer

The equations for the reactions are: $$CaCO3(s)\to CaO(s)+CO2(g)$$, $$2ZnS(s)+3O2(g)\to 2ZnO(s)+2SO2(g)$$, $$C3H8(g)+4H2O(g)\to 3CO(g)+10H2(g)$$, and $$SO2(g)+Na2S(aq)+Na2CO3(aq)\to CO2(g)+Na2S2O3(aq)$$

Step-by-step solution

Equation for (a)

Calcium carbonate (CaCO3) when heated decomposes into Calcium oxide (CaO) and Carbon Dioxide gas (CO2). The balanced chemical equation as per the stoichiometric coefficients can be represented as follows: $$CaCO3(s)\to CaO(s)+CO2(g)$$

Equation for (b)

Zinc Sulfide (ZnS) is heated in the presence of Oxygen gas (O2) to form Zinc Oxide (ZnO) and Sulfur Dioxide gas (SO2). The balanced chemical equation as per the stoichiometric coefficients can be represented as follows:$$2ZnS(s)+3O2(g)\to 2ZnO(s)+2SO2(g)$$

Equation for (c)

Propane gas (C3H8) reacts with gaseous water (H2O) to produce Carbon Monoxide (CO) and Hydrogen gas (H2). The balanced chemical equation as per the stoichiometric coefficients can be represented as follows:$$C3H8(g)+4H2O(g)\to 3CO(g)+10H2(g)$$

Equation for (d)

Sulfur Dioxide gas (SO2) is passed into an aqueous solution containing Sodium Sulfide (Na2S) and Sodium Carbonate (Na2CO3). The reaction produces Carbon Dioxide (CO2) and an aqueous solution of Sodium Thiosulfate (Na2S2O3). The balanced chemical equation as per the stoichiometric coefficients can be represented as follows:$$SO2(g)+Na2S(aq)+Na2CO3(aq)\to CO2(g)+Na2S2O3(aq)$$

Key concepts

Decomposition Reaction

Decomposition reactions are fascinating chemical processes where a single compound breaks down into two or more simpler substances. This transformation usually requires an input of energy, often in the form of heat, light, or electricity.

A classic example of a decomposition reaction is the breakdown of calcium carbonate (${\text{CaCO}}_3$) into calcium oxide ($\text{CaO}$) and carbon dioxide (${\text{CO}}_2$) when heated. Chemically, this is expressed as:

$${\text{CaCO}}_3(s)\to \text{CaO}(s)+{\text{CO}}_2(g)$$

Such reactions are crucial in various industries. For instance, the decomposition of limestone is a key step in cement production. Whenever you encounter a chemical compound breaking down into simpler substances, you are looking at a decomposition reaction.

Oxidation-Reduction (Redox)

Oxidation-reduction reactions, commonly known as redox reactions, are processes where electrons are transferred between substances. This results in a change in the oxidation states of atoms involved. Understanding these reactions is essential for grasping a broad range of chemical phenomena.

Let's take the example of zinc sulfide ($\text{ZnS}$) being heated in the presence of air. Zinc sulfide is converted to zinc oxide ($\text{ZnO}$) and sulfur dioxide (${\text{SO}}_2$):

$$2\text{ZnS}(s)+3{\text{O}}_2(g)\to 2\text{ZnO}(s)+2{\text{SO}}_2(g)$$

In this reaction, zinc is oxidized, as it loses electrons to form zinc oxide. Meanwhile, oxygen is reduced, as it gains electrons to form sulfur dioxide. Redox reactions play vital roles in energy production, metabolism, and corrosion.

Balanced Equations

Chemical equations need to be balanced to comply with the law of conservation of mass. This law states that matter cannot be created or destroyed in an isolated system. Therefore, each side of the equation must have the same number of atoms for each element.

Consider the reaction between propane gas and water vapor:
$${\text{C}}_3{\text{H}}_8(g)+4{\text{H}}_2\text{O}(g)\to 3\text{CO}(g)+10{\text{H}}_2(g)$$

Initially, the equation may not balance. By adjusting the stoichiometric coefficients, we ensure that the number of each type of atom is the same on both sides. Balancing chemical equations is crucial for accurately predicting the amounts of reactants and products in a chemical reaction. It allows chemists to determine ratios necessary for the reaction and is foundational for further calculations in stoichiometry.

Stoichiometry

Stoichiometry is the quantitative backbone of chemical reactions. It involves calculating the amounts of reactants and products involved in a chemical reaction. This concept is essential for understanding how much of each substance is needed or produced.

Taking the reaction of sulfur dioxide (${\text{SO}}_2$) with sodium sulfide and sodium carbonate, stoichiometry is used to find out the exact proportions:
$${\text{SO}}_2(g)+{\text{Na}}_2\text{S}(aq)+{\text{Na}}_2{\text{CO}}_3(aq)\to {\text{CO}}_2(g)+{\text{Na}}_2{\text{S}}_2{\text{O}}_3(aq)$$

Through stoichiometric calculations, we can predict how much ${\text{Na}}_2{\text{S}}_2{\text{O}}_3$ will be produced from given quantities of reactants. Stoichiometry guides chemists in planning for chemical syntheses and optimizing reaction conditions, forming a bridge between theoretical formulas and practical chemistry.