Problem 72 - Chemistry Matter and Change

Question

Write skeleton equations for these reactions. $$a.lithium+\text { gold (III) chloride }(a q) \rightarrow lithium chloride (a q)+gold(s)$$ $$\begin{array}{c}{\text { b. iron(s) }+\operatorname{tin}(\mathrm{IV}) \text { nitrate }(\mathrm{aq}) \rightarrow} \\ {\text { iron (\textrm{III} ) } \text { nitrate }(\mathrm{aq})+\operatorname{tin}(\mathrm{s})}\end{array}$$ $$\begin{array}{c}{\text { c. nickel(II) chloride(s) + oxygen (g) } \rightarrow} \\ {\text { nickel(II) oxide(s) + dichlorine pentoxide(g) }}\end{array}$$ $$\begin{array}{c}{\text { d. lithium chromate(aq) + barium chloride (aq) } \rightarrow} \\ {\text { lithium chloride(aq) }+\text { barium chromate(s) }}\end{array}$$

Step-by-Step Solution

Answer

Write the reactants and products for each reaction without balancing: a) Li + AuCl₃ → LiCl + Au; b) Fe + Sn(NO₃)₄ → Fe(NO₃)₃ + Sn; c) NiCl₂ + O₂ → NiO + Cl₂O₅; d) Li₂CrO₄ + BaCl₂ → LiCl + BaCrO₄.

Step 1: Understand the Skeleton Equation

A skeleton equation provides the formulas of reactants and products but does not indicate the quantities of each. Begin by writing the chemical formulas for all reactants and products based on the descriptions given without balancing.

Step 2: Reaction a: Lithium and Gold(III) Chloride

Identify the reactants and products from the given description. Reactants: lithium (Li) and gold(III) chloride (AuCl₃) in aqueous solution. Products: lithium chloride (LiCl) in aqueous solution and gold (Au) solid. Thus, the skeleton equation is: \[ \text{Li} + \text{AuCl}_3(aq) \rightarrow \text{LiCl}(aq) + \text{Au}(s) \]

Step 3: Reaction b: Iron and Tin(IV) Nitrate

Identify the reactants, which are iron (Fe) solid and tin(IV) nitrate (Sn(NO₃)₄) in aqueous solution. The products are iron(III) nitrate (Fe(NO₃)₃) in aqueous solution and tin (Sn) solid. Thus, the skeleton equation is: \[ \text{Fe}(s) + \text{Sn(NO}_3)_4(aq) \rightarrow \text{Fe(NO}_3)_3(aq) + \text{Sn}(s) \]

Step 4: Reaction c: Nickel(II) Chloride and Oxygen

For this reaction, the reactants are nickel(II) chloride (NiCl₂) solid and oxygen (O₂) gas. The products are nickel(II) oxide (NiO) solid and dichlorine pentoxide (Cl₂O₅) gas. The skeleton equation is given as: \[ \text{NiCl}_2(s) + \text{O}_2(g) \rightarrow \text{NiO}(s) + \text{Cl}_2\text{O}_5(g) \]

Step 5: Reaction d: Lithium Chromate and Barium Chloride

The reactants in this reaction are lithium chromate (Li₂CrO₄) in aqueous solution and barium chloride (BaCl₂) in aqueous solution. The products are lithium chloride (LiCl) in aqueous solution and barium chromate (BaCrO₄) solid. The skeleton equation is: \[ \text{Li}_2\text{CrO}_4(aq) + \text{BaCl}_2(aq) \rightarrow \text{LiCl}(aq) + \text{BaCrO}_4(s) \]

Key Concepts

Skeleton Equations

A skeleton equation is a basic way to represent a chemical reaction. It provides the chemical formulas for all reactants and products involved in a reaction. However, it does not show the amounts of each substance present, meaning the equation is not yet balanced. This form serves as the initial layout before balancing the equation to accurately represent the conservation of mass. For example, in the skeleton equation for a reaction between lithium and gold(III) chloride:

• Lithium is represented as \( \text{Li} \)
• Gold(III) chloride is \( \text{AuCl}_3 \)
• The products are \( \text{LiCl}\) and \( \text{Au} \)

This skeleton form is: \( \text{Li} + \text{AuCl}_3 \rightarrow \text{LiCl} + \text{Au} \). By using formulas instead of writing out names, skeleton equations make it easy to see how elements and compounds interact.
They provide a starting point for balancing the equation, which ensures that the same number of each type of atom is present on both sides of the equation.

Chemical Reactions

Chemical reactions involve the transformation of reactants into products. During a reaction, chemical bonds break in the reactants and new bonds form in the products. This process results in substances with different properties than the reactants. Reactions often release or absorb energy, depending on the nature of the process.
Reactions can be represented through equations, where the left side lists the reactants and the right side lists the products. For example, in the chemical reaction of iron with tin(IV) nitrate, the skeleton equation is \( \text{Fe}(s) + \text{Sn(NO}_3)_4(aq) \rightarrow \text{Fe(NO}_3)_3(aq) + \text{Sn}(s) \). Here:

• \( \text{Fe}(s) \) and \( \text{Sn(NO}_3)_4(aq) \) are the reactants
• \( \text{Fe(NO}_3)_3(aq) \) and \( \text{Sn}(s) \) are the products

This equation gives a concise description of what occurs in the reaction without showing the specific amounts of each substance required or produced. Understanding this helps in determining changes in properties and energy of the systems involved.

Reactants and Products

In any chemical reaction, reactants are the starting materials that react with each other, while products are the substances formed as a result of the reaction. Identifying these components is the first step in understanding and writing chemical equations.
For example, in the reaction between nickel(II) chloride and oxygen:

• Reactants: \( \text{NiCl}_2(s) \) and \( \text{O}_2(g) \)
• Products: \( \text{NiO}(s) \) and \( \text{Cl}_2\text{O}_5(g) \)

The reaction can be summarized as \( \text{NiCl}_2(s) + \text{O}_2(g) \rightarrow \text{NiO}(s) + \text{Cl}_2\text{O}_5(g) \).
The transition from reactants to products involves the breaking and forming of bonds, which may involve a change in physical state as well. Recognizing reactants and products in an equation is critical for balancing the equation and understanding the overall process occurring.

Aqueous Solutions

An aqueous solution is a solution where the solvent is water. It's denoted by the notation \((aq)\) next to a chemical formula. Many reactions occur in aqueous solutions, especially in biological and industrial processes, as water is a universal solvent.
In the example of lithium chromate reacting with barium chloride:

• Lithium chromate \( \text{Li}_2\text{CrO}_4(aq) \)
• Barium chloride \( \text{BaCl}_2(aq) \)
• Reaction products: lithium chloride \( \text{LiCl}(aq) \) and barium chromate \( \text{BaCrO}_4(s) \) as a solid precipitate

The skeleton equation is written as \( \text{Li}_2\text{CrO}_4(aq) + \text{BaCl}_2(aq) \rightarrow \text{LiCl}(aq) + \text{BaCrO}_4(s) \).
In such reactions, water is not usually included in the equation unless it directly participates as a reactant or product. Understanding which substances are in solution is important for predicting the behavior of ions and molecules in the reaction. It helps determine whether a reaction might produce a precipitate or remain homogeneous.