Problem 69 - Chemistry The Central Science

Question

Write a balanced equation for each of the following reactions: (a) Hydrogen cyanide is formed commercially by passing a mixture of methane, ammonia, and air over a catalyst at \(800^{\circ} \mathrm{C}\). Water is a by- product of the reaction. (b) Baking soda reacts with acids to produce carbon dioxide gas. (c) When barium carbonate reacts in air with sulfur dioxide, barium sulfate and carbon dioxide form.

Step-by-Step Solution

Answer

(a) \(2 CH4 + 2 NH3 + 3 O2 \rightarrow 2 HCN + 6 H2O\) (b) \(NaHCO3 + HA \rightarrow NaA + H2O + CO2\) (c) \(BaCO3 + SO2 \rightarrow BaSO4 + CO2\)

Step 1: (a) HCN formation from methane, ammonia, and air

Recall that hydrogen cyanide (HCN) forms commercially by passing a mixture of methane (CH4), ammonia (NH3), and air over a catalyst at 800°C. The air mainly consists of oxygen (O2). Water (H2O) is a by-product of the reaction. The unbalanced equation for the formation of HCN is: CH4 + NH3 + O2 -> HCN + H2O Now, we need to balance the equation. To do this, we will make sure the number of atoms of each element is equal on both sides. Balanced equation: 2 CH4 + 2 NH3 + 3 O2 -> 2 HCN + 6 H2O

Step 2: (b) Baking soda reaction with acids

Baking soda is chemically known as sodium bicarbonate (NaHCO3). When it reacts with acids, it forms carbon dioxide (CO2) gas. Generic acids can be represented as an acid molecule with a hydrogen, which we will represent as HA for this demonstration (acid type may vary). The unbalanced equation for this reaction is: NaHCO3 + HA -> CO2 + ? Now, we need to identify the other products of the reaction and balance the equation. In this case, when the acid reacts with the sodium bicarbonate, it will form a salt and water alongside CO2. The balanced equation will then be: NaHCO3 + HA -> NaA + H2O + CO2

Step 3: (c) Barium carbonate reacting with sulfur dioxide

In this reaction, barium carbonate (BaCO3) reacts with sulfur dioxide (SO2) in air. The products of the reaction are barium sulfate (BaSO4) and carbon dioxide (CO2). The unbalanced equation is: BaCO3 + SO2 -> BaSO4 + CO2 In this case, the equation is already balanced, as the number of atoms of each element is equal on both sides of the equation. Therefore, the balanced equation is: BaCO3 + SO2 -> BaSO4 + CO2

Key Concepts

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking and forming of chemical bonds. Every chemical reaction abides by the law of conservation of mass, meaning that the mass of the reactants equals the mass of the products. For this to hold true, the number of atoms of each element must be conserved during the reaction.

For instance, when hydrogen cyanide (HCN) is formed by passing methane (CH₄), ammonia (NH₃), and air over a catalyst at high temperatures, we witness a complex chemical reaction. The reaction requires precise conditions, including a catalyst and specific reactants, to yield HCN and water.

Stoichiometry

Stoichiometry is the quantitative relationship between the reactants and products in a chemical reaction. It relies on the mole concept to provide a means of calculating the amounts of substances involved in reactions. Stoichiometry is essential for balancing chemical equations because it ensures that the same quantity of each element is present on both sides of the equation, respecting the law of conservation of mass.

When baking soda (NaHCO₃) reacts with an acid (HA), stoichiometry determines the amounts of carbon dioxide (CO₂), water (H₂O), and the resultant salt (NaA) produced. Understanding stoichiometry is fundamental for predicting the outcomes of chemical reactions, whether it's in a controlled laboratory environment or an industrial setting.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They show the reactants on the left side, the products on the right, and an arrow pointing from left to right to indicate the direction of the reaction. The art of balancing chemical equations involves tweaking the coefficients—the numbers that appear before the chemical formulas—to ensure that the atoms are balanced on both sides, adhering to the stoichiometric principles.

An example is the reaction of barium carbonate (BaCO₃) with sulfur dioxide (SO₂). The chemical equation must reflect the conversion accurately, showing the formation of barium sulfate (BaSO₄) and carbon dioxide (CO₂). The simplicity of this reaction highlights that sometimes equations are naturally balanced, but usually, it requires careful adjustment and knowledge of reaction mechanisms.