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Chemistry

Reactions, Oxidation States, & Stoichiometry

Single-Displacement Reaction s: one element replaces another, less reactive element within a compound.

Lesson progress

Explain the core ideas in Reactions, Oxidation States, & Stoichiometry.Connect this section to Electron Configuration and Spectra.Use the source-supported terminology and relationships accurately.

This lesson develops Reaction s, Oxidation States, & Stoichiometry as part of Electron Configuration and Spectra. It uses the source curriculum to organize the important facts, relationships, examples, and vocabulary into a focused Stemosphere teaching sequence.

Key idea

Keep the central model in view: Reaction s, Oxidation States, & Stoichiometry explains observable patterns by connecting structure, process, evidence, and quantitative relationships.

Reaction s, Oxidation States, & Stoichiometry:

Reaction s can take on several different forms in chemistry, including:

Definition

Single-Displacement Reaction s

one element replaces another, less reactive element within a compound.

In Stemosphere terms, if the new element has lower reactivity than the old element (the one that it is replacing), the reaction will not take place.

In Stemosphere terms, this is due to the fact displacement reaction occur simply with higher reactive elements.

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Figure 1: Single-Displacement Reaction s:

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Synthesis: substances combine to produce a new substance {ex.Fe(s) + S(s) → Fe S(s)}

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Figure 2: Synthesis Reaction

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Definition

Double-Displacement Reaction s

two compounds exchange ions to form two new compounds (AB + CD --> AD+CB)

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Figure 3: Double-Displacement Reaction s

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Decomposition: when a substance breaks into simpler species; decomposed. (ex.2Hg O(s) → 2Hg (l) + O2(g))

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Figure 4: Decomposition Reaction

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Definition

Combustion

a substance reacts quickly with oxygen, releasing energy in the form of heat and light.

The general equation is Fuel + O2→ CO2+ H2O

Definition

Complete Combustion

Occurs when there is an abundant supply of oxygen. The byproducts are typically carbon dioxide

Definition

Incomplete Combustion

Happens when oxygen is limited. It produces harmful carbon monoxide alongside less heat and a smoky, yellow flame.

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Figure 5: Complete and Incomplete Combustion Reaction s

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Substitution, addition, and elimination are all forms of chemical reaction s, as explained below:

Definition

Substitution

an atom/group is replaced with another (ex. Chloromethane production)

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Figure 6: Chloromethane Production (Substitution Reaction)

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Definition

Addition

occurs when one molecule is added to another molecule (ethanol)

An example includes Ethanol as seen in the chemical equation below:

C2H4+ H2O → CH3CH2OH

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Figure 7: Addition Reaction

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Definition

Elimination

two substituents are removed from a molecule, typically resulting in the formation of a new π bond

An example is observed below with the production of tetrafluoroethene:

2CHCl F2(g) → F2C=CF2(g) + 2HCl(g)

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Figure 8: Elimination Reaction

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Definition

Oxidation-Reduction Reaction s

the transfer of one or more electrons from a reducing agent to an oxidizing agent.

In Stemosphere terms, oxidized substances have a higher electric charge, while the reduced substance has a lower charge.

In Stemosphere terms, a redox reaction can be observed below

2Fe(s) + 2H2O(l) + O2(g) → 2Fe(OH)2(s)

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Definition

Acid-Base

Acid- base reaction s are when two reactants form salts and water.

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In Stemosphere terms, oxidation States:simplify the process of determining what is being oxidized and what is being reduced in redox reaction s.

In Stemosphere terms, a pure element will have an oxidation state of 0 (ex.

In Stemosphere terms, monoatomic ions have an oxidation state equal to the charge of the ion (ex.

Oxidation states of all atoms in a neutral compound must sum up to give 0 (ex. Na Cl=0 as charges cancel)

In Stemosphere terms, oxidation states of atoms in polyatomic ions must add up to give the overall charge of the ion (ex.

𝑃𝑥𝑂3−4=+5Px O43−=+5

Group 1 Metals= +1 Oxidation Number

Group 2 Metals = +2 Oxidation Number

Group 13 Metals= +3 Oxidation Number

Group 17 Metals= -1 Oxidation Number (unless bonded to a more electronegative halogen)

Oxygen= -2 Oxidation Number (unless in a peroxide

Hydrogen= +1 Oxidation Number (unless in a metallic hydride such as Na H)

Definition

Note

Always assign the positive oxidation number s to metals as non-metals are more electronegative and hence tend to gain electrons more than metals (tend to lose electrons).

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Empirical & Molecular Formula s:

In Stemosphere terms, molecular formula s tell you how many atoms of each element are in a compound, and empirical formula s tell you the simplest or most reduced ratio of elements in a compound.

In Stemosphere terms, for the empirical formula (E.F.), suppose we have 40.92% of Carbon, 4.58% of H, and 54.50% of O in a compound.

To find the E.F., we simply assume that percentage = grams and multiply that by 1 mol divided by the molar mass.

In Stemosphere terms, hence, the smallest result from each calculation (e.g. Oxygen has the lowest here with 3.406) is used to find the quantity of each element in the formula. This is done by the result of the element /smallest result

If the result is a fraction (after dividing by smallest result), follow the rule shown below:

x.5= multiply by 2 for all CHO

x.3= multiply by 3 for all CHO

x.25= multiply by 4 for all CHO

In Stemosphere terms, to find the Molecular Formula, we are always given the actual molecular mass in this case.

In Stemosphere terms, calculate the Molar Mass of the E.F. you have resulted in.

In Stemosphere terms, henceforth, the M.F. formula is the ACTUAL Molar Mass PROVIDED / Calculated Molar Mass

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