Problem 11 - General Chemistry: Principles and Modern Applications

Question

Complete and balance the following equations. If no reaction occurs, so state. (a) \(\operatorname{TiCl}_{4}(\mathrm{g})+\mathrm{Na}(1) \stackrel{\Delta}{\longrightarrow}\) (b) \(\mathrm{Cr}_{2} \mathrm{O}_{3}(\mathrm{s})+\mathrm{Al}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow}\) (c) \(\mathrm{Ag}(\mathrm{s})+\mathrm{HCl}(\mathrm{aq}) \longrightarrow\) (d) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{aq})+\mathrm{KOH}(\mathrm{aq}) \longrightarrow\) (e) \(\mathrm{MnO}_{2}(\mathrm{s})+\mathrm{C}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow}\)

Step-by-Step Solution

Answer

The balanced equations are as follows:(a) \( \text{TiCl4(g)} + 4\text{Na(l)} \rightarrow \text{Ti(s)} + 4\text{NaCl(s)} \) (b) \( \text{Cr2O3(s)} + 2\text{Al(s)} \rightarrow \text{Al2O3(s)} + 2\text{Cr(s)} \) (c) No reaction(d) \( \text{K2Cr2O7(aq)} + 2\text{KOH(aq)} \rightarrow \text{2K2CrO4(aq) + H2O(l)} \)(e) \( \text{MnO2(s) + C(s)} \rightarrow \text{Mn(s) + CO2(g)} \)

Step 1: Complete and balance equation for TiCl4(g) + Na(l)

The reaction is between Titanium(IV) chloride (TiCl4) and Sodium metal (Na). The product of this reaction is Sodium chloride (NaCl) and Titanium (Ti). Therefore the completed chemical equation is \( \text{TiCl4(g)} + 4\text{Na(l)} \rightarrow \text{Ti(s)} + 4\text{NaCl(s)} \)

Step 2: Complete and balance equation for Cr2O3(s) + Al(s)

The reaction between Chromium(III) oxide (Cr2O3) and Aluminum metal (Al) produces Aluminum oxide (Al2O3) and Chromium (Cr). The completed and balanced chemical equation is \( \text{Cr2O3(s)} + 2\text{Al(s)} \rightarrow \text{Al2O3(s)} + 2\text{Cr(s)} \)

Step 3: Complete and balance equation for Ag(s) + HCl(aq)

The reaction is between Silver metal (Ag) and Hydrochloric acid (HCl). However, silver does not react with hydrochloric acid. So, in this case no reaction occurs.

Step 4: Complete and balance equation for K2Cr2O7(aq) + KOH(aq)

This reaction is between Potassium dichromate (K2Cr2O7) and Potassium hydroxide (KOH). The products of this reaction are Potassium chromate (K2CrO4), Water (H2O), and Potassium chloride (KCl). The completed balanced equation is \( \text{K2Cr2O7(aq)} + 2\text{KOH(aq)} \rightarrow \text{2K2CrO4(aq) + H2O(l)} \)

Step 5: Complete and balance equation for MnO2(s) + C(s)

The reaction is between Manganese(IV) oxide (MnO2) and Carbon (C). The products of this reaction will be Manganese (Mn) and Carbon dioxide (CO2). The completed balanced equation is \( \text{MnO2(s) + C(s)} \rightarrow \text{Mn(s) + CO2(g)} \)

Key Concepts

Reactivity Series

Understanding the reactivity series is crucial when predicting the outcomes of chemical reactions. The reactivity series is a list of elements organized by their ability to displace others in a compound. More reactive elements can displace less reactive elements from their compounds during a chemical reaction.

For example, in the exercise, aluminum (Al) is above chromium (Cr) in the reactivity series. This is why aluminum is capable of reducing chromium(III) oxide (Cr2O3) to chromium (Cr) in an oxidation-reduction reaction. The reaction can be represented by the equation \( \text{Cr2O3(s)} + 2\text{Al(s)} \rightarrow \text{Al2O3(s)} + 2\text{Cr(s)} \). Here, aluminum acts as a reducing agent, and chromium(III) oxide is reduced.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, commonly known as redox reactions, are processes that involve the transfer of electrons between elements. When an element gains electrons, it is reduced, and when an element loses electrons, it is oxidized.

In step 1 of the exercise solution, the equation \( \text{TiCl4(g)} + 4\text{Na(l)} \rightarrow \text{Ti(s)} + 4\text{NaCl(s)} \) involves sodium (Na) being oxidized as it loses electrons to form NaCl, whereas titanium tetrachloride (TiCl4) is reduced to titanium (Ti). The ability to correctly balance redox equations is essential in predicting the stoichiometry of the products formed in a reaction.

Chemical Reaction Types

Chemical reactions can be classified into several types, including synthesis, decomposition, single displacement, double displacement, and combustion. This classification helps in understanding the reaction mechanisms and predicting the products.

For instance, the reaction given in step 5, \( \text{MnO2(s) + C(s)} \rightarrow \text{Mn(s) + CO2(g)} \), is a type of redox reaction where manganese dioxide (MnO2) is reduced to manganese (Mn), and carbon (C) is oxidized to carbon dioxide (CO2). This particular reaction is also a decomposition reaction because a single compound (MnO2) breaks down into simpler substances (Mn and CO2). Noting the type of reaction helps in formulating and balancing the chemical equation.