Textbook Question
Reaction of A (green spheres) with B (blue spheres) is shown in the following diagram:
Which equation best describes the reaction?
a. A2 + 2 B → A2B2
b. 10 A + 5 B2 → 5 A2B2
c. 2 A + B2 → A2B2
d. 5 A + 5 B2 → 5 A2B2
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Ch.5 Classification & Balancing of Chemical Reactions
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
Chapter 5, Problem 23
Why is it not possible to balance an equation by changing the subscript on a substance, say from H2O to H2O2?
Verified step by step guidance1
Understand the role of subscripts in a chemical formula: Subscripts indicate the number of atoms of each element in a molecule. Changing a subscript alters the identity of the compound, creating a completely different substance with different chemical properties.
Recognize the purpose of balancing a chemical equation: The goal is to ensure the law of conservation of mass is obeyed, meaning the number of atoms of each element is the same on both sides of the equation. This is achieved by adjusting coefficients, not subscripts.
Consider the implications of changing a subscript: For example, changing H₂O (water) to H₂O₂ (hydrogen peroxide) would mean you are no longer working with the same compound. This fundamentally changes the reaction and violates the principle of balancing the original equation.
Focus on adjusting coefficients: Coefficients are numbers placed in front of chemical formulas to indicate the quantity of molecules or moles. Adjusting coefficients allows you to balance the equation without altering the identity of the substances involved.
Apply this understanding to any chemical equation: Always preserve the subscripts as they define the chemical identity of the substances. Use coefficients to balance the equation while maintaining the integrity of the compounds.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chemical Formula
A chemical formula represents the composition of a substance, indicating the types and numbers of atoms present. For example, H₂O indicates two hydrogen atoms and one oxygen atom, while H₂O₂ indicates two hydrogen atoms and two oxygen atoms. Changing the subscripts alters the identity of the substance, leading to different chemical properties and reactions.
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Chemical Reaction: Chemical Change Concept 2
Law of Conservation of Mass
The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. This principle requires that the number of atoms of each element must be the same on both sides of a chemical equation. Changing subscripts would violate this law, as it would change the number of atoms and thus the mass of the reactants and products.
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01:48Law of Conservation of Mass
Balancing Chemical Equations
Balancing chemical equations involves adjusting coefficients (the numbers in front of compounds) to ensure that the same number of each type of atom appears on both sides of the equation. This process maintains the integrity of the substances involved while adhering to the Law of Conservation of Mass. Changing subscripts instead of coefficients would misrepresent the actual substances and their quantities.
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01:32Balancing Chemical Equations (Simplified) Concept 1
Related Practice
Textbook Question
Which of the following equations are balanced? Balance those that need it.
a. CaC2 + 2 H2O → Ca(OH)2 +C2H2
b. C2H8N2 + 2 N2O4 → 2 N2 + 2 CO2 + 4 H2O
c. 3 MgO + 2 Fe → Fe2O3 + 3 Mg
d. N2O → N2 + O2
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Textbook Question
When sodium metal is placed in water, the following change occurs: Sodium, Na(s) + Water, H2O(l) → Hydrogen, H2(g) + Sodium hydroxide, NaOH(aq)
a. Identify the reactants and products and their physical states
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Textbook Question
What is meant by the term 'balanced equation'?
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Textbook Question
In each of the following, tell whether the substance gains electrons or loses electrons in a redox reaction:
a. An oxidizing agent
b. A reducing agent
c. A substance undergoing oxidation
d. A substance undergoing reduction
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Textbook Question
An aqueous solution of a cation (represented as blue spheres in the diagram) is allowed to mix with a solution of an anion (represented as green spheres) and the following result is obtained:
Which combinations of cation and anion, chosen from the following lists, are compatible with the observed results? Explain.
Cations: Na+, Ca2+, Ag+, Ni2+
Anions: Cl−, CO23–, CrO42–, NO3–
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