Question

Complete and balance the following equations: (a) \(\mathrm{ZnCO}_{3}(s) \stackrel{\Delta}{\longrightarrow}\) (b) \(\mathrm{BaC}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (c) \(\mathrm{C}_{2} \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow\) (d) \(\mathrm{CS}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow\) (e) \(\mathrm{Ca}(\mathrm{CN})_{2}(s)+\operatorname{HBr}(a q)\)

Short answer

(a) \(ZnCO_3 (s) \stackrel{\Delta}{\longrightarrow} ZnO (s) + CO_2 (g)\) (b) \(BaC_2 (s) + 2 H_2O (l) \rightarrow Ba(OH)_2 (aq) + C_2H_2 (g)\) (c) \(2 C_2H_2 (g) + 5 O_2 (g) \rightarrow 4 CO_2 (g) + 2 H_2O (g)\) (d) \(CS_2 (g) + 3 O_2 (g) \rightarrow CO_2 (g) + 2 SO_2 (g)\) (e) \(Ca(CN)_2 (s) + 2 HBr (aq) \rightarrow CaBr_2 (aq) + 2 HCN (aq)\)

Step-by-step solution

(a) Complete the equation for ZnCO3 (s) decomposition

For the decomposition of ZnCO3 (s) induced by heat, the products will be zinc oxide (ZnO) and carbon dioxide (CO2). The balanced equation: ZnCO3 (s) ∆→ ZnO (s) + CO2 (g)

(b) Complete the equation for the reaction between BaC2 (s) and H2O (l)

The reaction between barium carbide (BaC2) and water (H2O) produces calcium hydroxide (Ba(OH)2) and acetylene gas (C2H2). The balanced equation: BaC2 (s) + 2 H2O (l) → Ba(OH)2 (aq) + C2H2 (g)

(c) Complete the equation for the combustion of C2H2 (g) in O2 (g)

The combustion of acetylene (C2H2) in the presence of oxygen (O2) produces carbon dioxide (CO2) and water (H2O). The balanced equation: 2 C2H2 (g) + 5 O2 (g) → 4 CO2 (g) + 2 H2O (g)

(d) Complete the equation for the reaction between CS2 (g) and O2 (g)

The reaction between carbon disulfide (CS2) and oxygen (O2) produces sulfur dioxide (SO2) and carbon dioxide (CO2). The balanced equation: CS2 (g) + 3 O2 (g) → CO2 (g) + 2 SO2 (g)

(e) Complete the equation for the reaction between Ca(CN)2 (s) and HBr (aq)

The reaction between calcium cyanide (Ca(CN)2) and hydrobromic acid (HBr) produces calcium bromide (CaBr2), hydrogen cyanide (HCN), and water (H2O). The balanced equation: Ca(CN)2 (s) + 2 HBr (aq) → CaBr2 (aq) + 2 HCN (aq)

Key concepts

Balancing Equations

Balancing chemical equations is crucial because it ensures that the same number of each type of atom is present on both sides of the equation. In essence, it obeys the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. To balance an equation, you typically follow these steps:

• Write down the unbalanced equation with the formulas for all reactants and products.
• Adjust the coefficients (numbers in front of the molecules) to balance the atoms for each element on both sides.
• Check the balance by confirming that each type of atom has the same number on either side of the reaction arrow.
• Ensure that the coefficients are in the simplest possible ratio.

Balancing requires practice and careful attention to detail, especially when working with complex reactions.

Decomposition Reactions

Decomposition reactions involve a single compound breaking down into two or more simpler substances. This type of reaction generally requires an input of energy, such as heat, to occur. Here's how a decomposition reaction works:

• A single compound, known as the reactant, is heated or electrified.
• This causes bonds within the compound to break apart.
• The original compound splits into two or more simpler products.

For example, in the decomposition of zinc carbonate (ZnCO\(_3\)), heat causes the compound to break down into zinc oxide (ZnO) and carbon dioxide (CO\(_2\)). This reaction plays a significant role in various industrial processes.

Combustion Reactions

Combustion reactions occur when a substance reacts rapidly with oxygen, releasing energy in the form of heat and light. These reactions usually involve hydrocarbons and can be seen in everyday processes such as burning fuel. The key points of a combustion reaction are:

• The reactant (often a hydrocarbon) combines with oxygen.
• This produces oxides, commonly carbon dioxide (CO\(_2\)) and water (H\(_2\)O).
• Combustion is exothermic, meaning it releases energy.
• Complete combustion has excess oxygen, while incomplete combustion has limited oxygen, forming carbon monoxide (CO) and soot.

A classic example is the combustion of acetylene (C\(_2\)H\(_2\)), where in the presence of enough oxygen, it yields carbon dioxide and water.

Reaction Products

Understanding reaction products is essential for predicting what substances will result from a chemical reaction. Every chemical equation includes reactants that transform into products, which are the new substances formed. Here are some important aspects:

• Reaction products depend on the reactants and the type of reaction occurring.
• The nature of the products can include gases, solids, or liquids.
• For decomposition reactions, the products are simpler substances than the reactant.
• In combustion, products typically include oxides such as carbon dioxide and water.

Knowing the expected products helps in understanding chemical processes and their impacts, such as environmental consequences in combustion reactions.