5.E: Introduction to Chemical Reactions (Exercises)

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Additional Exercises

Isooctane (C₈H₁₈) is used as a standard for comparing gasoline performance. Write a balanced chemical equation for the combustion of isooctane.
Heptane (C₇H₁₆), like isooctane (see Exercise 1), is also used as a standard for determining gasoline performance. Write a balanced chemical equation for the combustion of heptane.
What is the difference between a combination reaction and a redox reaction? Are all combination reactions also redox reactions? Are all redox reactions also combination reactions?
Are combustion reactions always redox reactions as well? Explain.
A friend argues that the equation

Fe²⁺ + Na → Fe + Na⁺

is balanced because each side has one iron atom and one sodium atom. Explain why your friend is incorrect.
Some antacids contain aluminum hydroxide [Al(OH)₃]. This compound reacts with excess hydrochloric acid (HCl) in the stomach to neutralize it. If the products of this reaction are water and aluminum chloride, what is the balanced chemical equation for this reaction? What is the stoichiometric ratio between the number of HCl molecules made to the number of H₂O molecules made?
Sulfuric acid is made in a three-step process: (1) the combustion of elemental sulfur to produce sulfur dioxide, (2) the continued reaction of sulfur dioxide with oxygen to produce sulfur trioxide, and (3) the reaction of sulfur trioxide with water to make sulfuric acid (H₂SO₄). Write balanced chemical equations for all three reactions.
If the products of glucose metabolism are carbon dioxide and water, what is the balanced chemical equation for the overall process? What is the stoichiometric ratio between the number of CO₂ molecules made to the number of H₂O molecules made?
Historically, the first true battery was the Leclanché cell, named after its discoverer, Georges Leclanché. It was based on the following reaction:

Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)

Identify what is being oxidized, what is being reduced, and the respective reducing and oxidizing agents.

Answers

1. 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O

2. C₇H₁₆ + 11O₂→ 7CO₂+ 8H₂O

A combination reaction makes a new substance from more than one reactant; a redox reaction rearranges electrons. Most (not all) combination reactions are redox reactions. Not all redox reactions are combination reactions.

4. All combustion reactions are redox reactions. In combustion a chemical is combining with oxygen and that chemical is being oxidized. Oxygen, on the other hand, is being reduced.

Your friend is incorrect because the number of electrons transferring is not balanced. A balanced equation must not only have the same number of atoms of each element on each side of the equation but must also have the same charge on both sides.

6. Al(OH)₃ + 3HCl → 3H₂O + AlCl₃; 1:1

(1) S + O₂ → SO₂; (2) 2SO₂ + O₂ → 2SO₃; (3) SO₃ + H₂O → H₂SO₄

8. C₆H₁₂O₆ + 6O₂→ 6CO₂+ 6H₂O; 1:1

oxidized and reducing agent: Zn; reduced and oxidizing agent: Cu²⁺